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Quantum Mechanical Ideas
Photons and their energyWhen electromagnetic
waves are exhibiting their ldquoparticle-likerdquo nature we call those little mass-less bundles of energy PHOTONS
There are photons of light photons of UV photons of microwaves photons of IR etc
Sometimes the wavelengths of photons are measured in meters sometimes in
nanometers and sometimes in Angstroms where
one Angstrom = 1 x 10-10 meters
Also the ENERGY of electrons is often given in ldquoelectron-Voltsrdquo eV instead of
Joules where
one eV = 16 x 10-19 J-
a very tiny amount of energy
New Units of measurement
All electromagnetic photons carry energy as they travel along at ldquothe speed of lightrdquo
The energy of a photon in eV is given by
E = hf where
f is the frequency of the photon measured in Hertz
h is a constant called Plankrsquos constanth = 414 x 10-15 eVmiddots
Orh = 663 x 10-34 Jmiddots
For photonslike ldquovisible lightrdquo UV IR
microwaves etc
c = f
where c = the ldquospeed of lightrdquo
c = 3 x 108 ms
The difference frequency of electromagnetic waves (photons) determines if they are
visible light radio wave microwaves etc
higher frequency = more energy
Which photon has more energy- an X-ray photon or a microwave photon
The different frequencies of visible light correspond to different colors of light
Blue light has a higher frequency than yellow light Which color of light has the highest energy
How can you produce different colors of light
What makes one atom
different from another
The amazing colors produced in fireworks are a result of the different types of atoms that are used to make the fireworks
Each atom has its own unique number of protons neutrons and electrons
Each electron in every element is in an ldquoorbitalrdquo about the nucleus and has a unique energy
That unique energy determines the amazing colors seen in fireworks
bull A Quantum is a discreet unit of a physical quantitybull For example our money is measured in a quantum of
one cent You can have 1 cent 2 cents 8 cents etc but you canrsquot have 124 cents or 1968 cents You must jump from 1 to 2 to 3 to 4 etc
bull Electric charge which ultimately comes from either a proton or an electron is QUANTIZED
bull There is no such thing as a half of an electron or a fifth of a proton so everything that has electrical charge must have some multiple of the charge of an electron or proton- 5 electrons 8 protons etc Thatrsquos why electric charge is QUANTIZED
The electrons in their orbitals about the nucleus have QUANTIZED levels of energy that are determined by which orbital they are in
The orbitals are numbered with ldquonrdquo numbers the ldquoprinciple quantum numberrdquo
n = 1 n = 2 n = 3 etc where the orbital closest to the nucleus is n = 1
The ldquon-numberrdquo for each atomrsquos electrons determine that electronrsquos energy
The larger the ldquonrdquo the larger the energy
What does the energy of an electron in its orbital have to do with the colors of fireworks
When an electron absorbs energy from an external source in any form (heat electricity a collision etc) it jumps to a higher orbital- called an ldquoexcited staterdquo
When the electron falls back down to its original orbital called its ldquorest staterdquo or ldquoground staterdquo it must give up that extra energy The energy is emitted in the form of a photon
Some of those emitted photons are visible light of different colors- some photons are not visible to us like UV or IR or microwaves or X-rays
If an atom is continually absorbing energy all kinds of transitions between higher and lower orbital levels are possible resulting in many different types of emitted photons of many different colors
Metal Color
Strontium Red
Copper Blue
Barium Green
Sodium YellowOrange
Calcium Orange
Gold Iron
What elements are used in fireworks to produce different
colors of light
Atomic Spectra
bull Since the electronsrsquo energy are unique for each element each element produces a unique spectra of colors when supplied energy
bull We may see with our eyes only many overlaping colors of light To see all the distinct colors in the atomrsquos spectra requires a ldquodiffraction gratingrdquo
Spectra for Neon
Each element produces a unique spectra of colored lines when viewed through a diffraction grating
Argon
Helium
Nitrogen
Mercury
Because each element produces a unique emission spectra scientists use ldquospectral analysisrdquo to determine the composition of unknown substances The spectra is like a fingerprint- absolutely unique for each element
Astronomers use ldquospectral analysisrdquo to determine the composition of stars as well
Argon
Using a Spectrometer to determine the identity of a elemental gas
1 The gas will not glow until it is energized Energy can be provided in the form of heat or by applying a high voltage The spectrum analysis power supply shown here provides high voltage
2 If you look at the glowing tube with just a diffraction grating the emission spectrum lines of color are visible
3 If you look at the glowing tube through a ldquospectrometerrdquo which contains a diffraction grating you can actually precisely measure the angles between the lines
4 Those angles allow you to precisely determine the wavelengths (or frequencies) of each of those colors
5 Since each element emits only certain wavelengths the gas can be identified
HydrogenThe emission spectrum of
Hydrogen is the most studied spectrum because it is also the simplest
Hydrogen has only ONE electron
But that ONE electron can be energized to many different orbitals ldquoexcited statesrdquo and will emit photons as it returns to its ldquoground staterdquo
Suppose an electron makes a transition from n = 3 to n = 2 What is the energy of the emitted photon
Energy = E3 ndash E2
E = 1207 eV ndash 1019 eV
E = 188 eV
What is the energy of an emitted photon if an electron makes a transition from n = 4 to n = 1
E = 1273 eVThe higher the energy of the photon the higher its frequency
E = hf
Each color has a different energy The further apart the lines the greater the difference in energy The closer the lines the less the difference in energy
Look at the spectrum for Hydrogen Which two lines have the least difference in energy Which two lines have the greatest difference in energy
Atomic SpectraAbsorption of an external source of
energy results in a transition to a higher energy level
bull A transition back to a lower level must release energy ndash in the form of a photon
bull The frequency of the emitted photon is determined by the difference in the energy levels
Ephoton = E2 ndash E1
Since E = hf the higher the energy the higher the frequency
bull Different frequencies are different colors of light or different types of EM Waves
The Hydrogen
AtomONE
electron
The frequency of the emitted photon is determined by the difference in the energy levelsEphoton = hf = E2 ndash E1
Now you try onehellipbull Get out your calculatorsbull The energized electron in Hydrogen makes a
transition from n = 3 with an energy of -15 eV down to its ground state where its energy is -136 eV
What is the frequency of the emitted photonbull Ephoton = E2 ndash E1 and Ephoton = hfbull Ephoton = -15 eV ndash (-136 eV) = 121 eVbull Ephoton = 121 eV = hf (h = 414 x 10-15 eVs )bull f = 121 eV divide 414 x 10-15 eVs = bull Frequency f = 292 x 1015 Hzbull Is this visible light Use c = f to find the
wavelengthbull wavelength = 102 x 10-7 = 102 nmbull This is NOT visible light- it is UV
Hydrogen EmissionThe energy in eV of the electron in a Hydrogen atom is given by
E =
1Find the energy of the electron at each orbit from n = 1 to n = 7
2 Find the Energy of each photon emitted (Ephoton = E) for these transitions from one orbit to another
4 to 1 5 to 2 6 to 3 7 to 4
3 to 1 4 to 2 5 to 3 6 to 4
2 to 1 3 to 2 4 to 3 5 to 4
3 Find the wavelength for each of those photons and determine what type of electromagnetic wave they are
2n
eV613
Light behaves like a wave AND like a particle
The first clear demonstration of the particle-like behavior of light was in
The Photoelectric Effect
Albert Einstein won the Nobel Prize in Physics for his study of the Photoelectric Effect
Shining light on a metal can liberate electrons from its surface
The light has to have enough energy (high enough frequency) for this effect to occur
The energy of the ldquophotoelectronsrdquo liberated from the surface depends on the frequency (the energy) of that incident light- NOT its intensity
Increasing the intensity of the light increases the number of photoelectrons emitted but not the energy of each photoelectron
When will Photoelectrons be producedPHet simulation
(Go to PHet website to explore the photoelectric effect simulation)
If no electrons are ejected you musthelliphellipincrease the frequency of the lightIf only a few electrons are ejected and you want
more your musthelliphellipincrease the intensity of the lightIf you want to increase the kinetic energy of the
electrons you musthelliphellipincrease the frequency of the light
hellip and the mathhellipUsing conservation of energyThe energy of the incident photon disappears
Where does it goFirst that energy must be used to liberate the
electron That energy is called the WORK FUNCTION WO Each kind of metal has its unique work function
Any extra energy is given appears in the electron as kinetic energy K
Photon Energy = Work function + Kinetic energy
E = Wo + K
ExamplePhoton energy = Wo + K
A photon with energy 32 eV strikes a metal surface with a work function of 18 eV What is the kinetic energy of the ejected photoelectrons
K = photon energy ndash Wo
K = 32 eV ndash 18 eV
K = 14 eV
ExamplePhoton energy = Wo + K
A photon with energy 28 eV strikes a metal surface If the kinetic energy of the ejected photoelectrons is 05 eV what is the work function of the metal
Wo = photon energy - K
Wo = 28 eV ndash 05 eV
Wo = 23 eV
hf = Wo + frac12 mv2
There is a minimum frequency called the ldquothreshold frequencyrdquo required to liberate an electron At the threshold frequency
Energy of photon = hfthreshold = Wo
That threshold photonrsquos wavelength is called the ldquocutoff wavelengthrdquo and can be found
using
c = f
Now you try some
If the cut-off wavelength for a particular metal is 320 nm what is the metalrsquos work function
First find the threshold frequency using c = f
Threshold frequency fo = 938 x 1014 Hz
Now find the work-function hfo = Wo
Be careful to use Planckrsquos constant with the correct units
h = 663 x 10-34Jmiddots or h = 414 x 10-15 eVmiddots
Wo = 622 x 10-19 J or Wo = 388 eV
What if a 450 nm light hit a surface with a work function of 236 eV What will be the kinetic energy of the photoelectron
First find the frequency of the 450 nm lightf = 667 x 1014 HzNow using conservation of energy
hf = Wo + Kinetic energySo K = hf ndash WoK = 040 eV How fast is the ejected electron movingK = frac12 mv2 m = 91 x 10-31 kg AND you have
to convert K back into Joules first
Photons and their energyWhen electromagnetic
waves are exhibiting their ldquoparticle-likerdquo nature we call those little mass-less bundles of energy PHOTONS
There are photons of light photons of UV photons of microwaves photons of IR etc
Sometimes the wavelengths of photons are measured in meters sometimes in
nanometers and sometimes in Angstroms where
one Angstrom = 1 x 10-10 meters
Also the ENERGY of electrons is often given in ldquoelectron-Voltsrdquo eV instead of
Joules where
one eV = 16 x 10-19 J-
a very tiny amount of energy
New Units of measurement
All electromagnetic photons carry energy as they travel along at ldquothe speed of lightrdquo
The energy of a photon in eV is given by
E = hf where
f is the frequency of the photon measured in Hertz
h is a constant called Plankrsquos constanth = 414 x 10-15 eVmiddots
Orh = 663 x 10-34 Jmiddots
For photonslike ldquovisible lightrdquo UV IR
microwaves etc
c = f
where c = the ldquospeed of lightrdquo
c = 3 x 108 ms
The difference frequency of electromagnetic waves (photons) determines if they are
visible light radio wave microwaves etc
higher frequency = more energy
Which photon has more energy- an X-ray photon or a microwave photon
The different frequencies of visible light correspond to different colors of light
Blue light has a higher frequency than yellow light Which color of light has the highest energy
How can you produce different colors of light
What makes one atom
different from another
The amazing colors produced in fireworks are a result of the different types of atoms that are used to make the fireworks
Each atom has its own unique number of protons neutrons and electrons
Each electron in every element is in an ldquoorbitalrdquo about the nucleus and has a unique energy
That unique energy determines the amazing colors seen in fireworks
bull A Quantum is a discreet unit of a physical quantitybull For example our money is measured in a quantum of
one cent You can have 1 cent 2 cents 8 cents etc but you canrsquot have 124 cents or 1968 cents You must jump from 1 to 2 to 3 to 4 etc
bull Electric charge which ultimately comes from either a proton or an electron is QUANTIZED
bull There is no such thing as a half of an electron or a fifth of a proton so everything that has electrical charge must have some multiple of the charge of an electron or proton- 5 electrons 8 protons etc Thatrsquos why electric charge is QUANTIZED
The electrons in their orbitals about the nucleus have QUANTIZED levels of energy that are determined by which orbital they are in
The orbitals are numbered with ldquonrdquo numbers the ldquoprinciple quantum numberrdquo
n = 1 n = 2 n = 3 etc where the orbital closest to the nucleus is n = 1
The ldquon-numberrdquo for each atomrsquos electrons determine that electronrsquos energy
The larger the ldquonrdquo the larger the energy
What does the energy of an electron in its orbital have to do with the colors of fireworks
When an electron absorbs energy from an external source in any form (heat electricity a collision etc) it jumps to a higher orbital- called an ldquoexcited staterdquo
When the electron falls back down to its original orbital called its ldquorest staterdquo or ldquoground staterdquo it must give up that extra energy The energy is emitted in the form of a photon
Some of those emitted photons are visible light of different colors- some photons are not visible to us like UV or IR or microwaves or X-rays
If an atom is continually absorbing energy all kinds of transitions between higher and lower orbital levels are possible resulting in many different types of emitted photons of many different colors
Metal Color
Strontium Red
Copper Blue
Barium Green
Sodium YellowOrange
Calcium Orange
Gold Iron
What elements are used in fireworks to produce different
colors of light
Atomic Spectra
bull Since the electronsrsquo energy are unique for each element each element produces a unique spectra of colors when supplied energy
bull We may see with our eyes only many overlaping colors of light To see all the distinct colors in the atomrsquos spectra requires a ldquodiffraction gratingrdquo
Spectra for Neon
Each element produces a unique spectra of colored lines when viewed through a diffraction grating
Argon
Helium
Nitrogen
Mercury
Because each element produces a unique emission spectra scientists use ldquospectral analysisrdquo to determine the composition of unknown substances The spectra is like a fingerprint- absolutely unique for each element
Astronomers use ldquospectral analysisrdquo to determine the composition of stars as well
Argon
Using a Spectrometer to determine the identity of a elemental gas
1 The gas will not glow until it is energized Energy can be provided in the form of heat or by applying a high voltage The spectrum analysis power supply shown here provides high voltage
2 If you look at the glowing tube with just a diffraction grating the emission spectrum lines of color are visible
3 If you look at the glowing tube through a ldquospectrometerrdquo which contains a diffraction grating you can actually precisely measure the angles between the lines
4 Those angles allow you to precisely determine the wavelengths (or frequencies) of each of those colors
5 Since each element emits only certain wavelengths the gas can be identified
HydrogenThe emission spectrum of
Hydrogen is the most studied spectrum because it is also the simplest
Hydrogen has only ONE electron
But that ONE electron can be energized to many different orbitals ldquoexcited statesrdquo and will emit photons as it returns to its ldquoground staterdquo
Suppose an electron makes a transition from n = 3 to n = 2 What is the energy of the emitted photon
Energy = E3 ndash E2
E = 1207 eV ndash 1019 eV
E = 188 eV
What is the energy of an emitted photon if an electron makes a transition from n = 4 to n = 1
E = 1273 eVThe higher the energy of the photon the higher its frequency
E = hf
Each color has a different energy The further apart the lines the greater the difference in energy The closer the lines the less the difference in energy
Look at the spectrum for Hydrogen Which two lines have the least difference in energy Which two lines have the greatest difference in energy
Atomic SpectraAbsorption of an external source of
energy results in a transition to a higher energy level
bull A transition back to a lower level must release energy ndash in the form of a photon
bull The frequency of the emitted photon is determined by the difference in the energy levels
Ephoton = E2 ndash E1
Since E = hf the higher the energy the higher the frequency
bull Different frequencies are different colors of light or different types of EM Waves
The Hydrogen
AtomONE
electron
The frequency of the emitted photon is determined by the difference in the energy levelsEphoton = hf = E2 ndash E1
Now you try onehellipbull Get out your calculatorsbull The energized electron in Hydrogen makes a
transition from n = 3 with an energy of -15 eV down to its ground state where its energy is -136 eV
What is the frequency of the emitted photonbull Ephoton = E2 ndash E1 and Ephoton = hfbull Ephoton = -15 eV ndash (-136 eV) = 121 eVbull Ephoton = 121 eV = hf (h = 414 x 10-15 eVs )bull f = 121 eV divide 414 x 10-15 eVs = bull Frequency f = 292 x 1015 Hzbull Is this visible light Use c = f to find the
wavelengthbull wavelength = 102 x 10-7 = 102 nmbull This is NOT visible light- it is UV
Hydrogen EmissionThe energy in eV of the electron in a Hydrogen atom is given by
E =
1Find the energy of the electron at each orbit from n = 1 to n = 7
2 Find the Energy of each photon emitted (Ephoton = E) for these transitions from one orbit to another
4 to 1 5 to 2 6 to 3 7 to 4
3 to 1 4 to 2 5 to 3 6 to 4
2 to 1 3 to 2 4 to 3 5 to 4
3 Find the wavelength for each of those photons and determine what type of electromagnetic wave they are
2n
eV613
Light behaves like a wave AND like a particle
The first clear demonstration of the particle-like behavior of light was in
The Photoelectric Effect
Albert Einstein won the Nobel Prize in Physics for his study of the Photoelectric Effect
Shining light on a metal can liberate electrons from its surface
The light has to have enough energy (high enough frequency) for this effect to occur
The energy of the ldquophotoelectronsrdquo liberated from the surface depends on the frequency (the energy) of that incident light- NOT its intensity
Increasing the intensity of the light increases the number of photoelectrons emitted but not the energy of each photoelectron
When will Photoelectrons be producedPHet simulation
(Go to PHet website to explore the photoelectric effect simulation)
If no electrons are ejected you musthelliphellipincrease the frequency of the lightIf only a few electrons are ejected and you want
more your musthelliphellipincrease the intensity of the lightIf you want to increase the kinetic energy of the
electrons you musthelliphellipincrease the frequency of the light
hellip and the mathhellipUsing conservation of energyThe energy of the incident photon disappears
Where does it goFirst that energy must be used to liberate the
electron That energy is called the WORK FUNCTION WO Each kind of metal has its unique work function
Any extra energy is given appears in the electron as kinetic energy K
Photon Energy = Work function + Kinetic energy
E = Wo + K
ExamplePhoton energy = Wo + K
A photon with energy 32 eV strikes a metal surface with a work function of 18 eV What is the kinetic energy of the ejected photoelectrons
K = photon energy ndash Wo
K = 32 eV ndash 18 eV
K = 14 eV
ExamplePhoton energy = Wo + K
A photon with energy 28 eV strikes a metal surface If the kinetic energy of the ejected photoelectrons is 05 eV what is the work function of the metal
Wo = photon energy - K
Wo = 28 eV ndash 05 eV
Wo = 23 eV
hf = Wo + frac12 mv2
There is a minimum frequency called the ldquothreshold frequencyrdquo required to liberate an electron At the threshold frequency
Energy of photon = hfthreshold = Wo
That threshold photonrsquos wavelength is called the ldquocutoff wavelengthrdquo and can be found
using
c = f
Now you try some
If the cut-off wavelength for a particular metal is 320 nm what is the metalrsquos work function
First find the threshold frequency using c = f
Threshold frequency fo = 938 x 1014 Hz
Now find the work-function hfo = Wo
Be careful to use Planckrsquos constant with the correct units
h = 663 x 10-34Jmiddots or h = 414 x 10-15 eVmiddots
Wo = 622 x 10-19 J or Wo = 388 eV
What if a 450 nm light hit a surface with a work function of 236 eV What will be the kinetic energy of the photoelectron
First find the frequency of the 450 nm lightf = 667 x 1014 HzNow using conservation of energy
hf = Wo + Kinetic energySo K = hf ndash WoK = 040 eV How fast is the ejected electron movingK = frac12 mv2 m = 91 x 10-31 kg AND you have
to convert K back into Joules first
Sometimes the wavelengths of photons are measured in meters sometimes in
nanometers and sometimes in Angstroms where
one Angstrom = 1 x 10-10 meters
Also the ENERGY of electrons is often given in ldquoelectron-Voltsrdquo eV instead of
Joules where
one eV = 16 x 10-19 J-
a very tiny amount of energy
New Units of measurement
All electromagnetic photons carry energy as they travel along at ldquothe speed of lightrdquo
The energy of a photon in eV is given by
E = hf where
f is the frequency of the photon measured in Hertz
h is a constant called Plankrsquos constanth = 414 x 10-15 eVmiddots
Orh = 663 x 10-34 Jmiddots
For photonslike ldquovisible lightrdquo UV IR
microwaves etc
c = f
where c = the ldquospeed of lightrdquo
c = 3 x 108 ms
The difference frequency of electromagnetic waves (photons) determines if they are
visible light radio wave microwaves etc
higher frequency = more energy
Which photon has more energy- an X-ray photon or a microwave photon
The different frequencies of visible light correspond to different colors of light
Blue light has a higher frequency than yellow light Which color of light has the highest energy
How can you produce different colors of light
What makes one atom
different from another
The amazing colors produced in fireworks are a result of the different types of atoms that are used to make the fireworks
Each atom has its own unique number of protons neutrons and electrons
Each electron in every element is in an ldquoorbitalrdquo about the nucleus and has a unique energy
That unique energy determines the amazing colors seen in fireworks
bull A Quantum is a discreet unit of a physical quantitybull For example our money is measured in a quantum of
one cent You can have 1 cent 2 cents 8 cents etc but you canrsquot have 124 cents or 1968 cents You must jump from 1 to 2 to 3 to 4 etc
bull Electric charge which ultimately comes from either a proton or an electron is QUANTIZED
bull There is no such thing as a half of an electron or a fifth of a proton so everything that has electrical charge must have some multiple of the charge of an electron or proton- 5 electrons 8 protons etc Thatrsquos why electric charge is QUANTIZED
The electrons in their orbitals about the nucleus have QUANTIZED levels of energy that are determined by which orbital they are in
The orbitals are numbered with ldquonrdquo numbers the ldquoprinciple quantum numberrdquo
n = 1 n = 2 n = 3 etc where the orbital closest to the nucleus is n = 1
The ldquon-numberrdquo for each atomrsquos electrons determine that electronrsquos energy
The larger the ldquonrdquo the larger the energy
What does the energy of an electron in its orbital have to do with the colors of fireworks
When an electron absorbs energy from an external source in any form (heat electricity a collision etc) it jumps to a higher orbital- called an ldquoexcited staterdquo
When the electron falls back down to its original orbital called its ldquorest staterdquo or ldquoground staterdquo it must give up that extra energy The energy is emitted in the form of a photon
Some of those emitted photons are visible light of different colors- some photons are not visible to us like UV or IR or microwaves or X-rays
If an atom is continually absorbing energy all kinds of transitions between higher and lower orbital levels are possible resulting in many different types of emitted photons of many different colors
Metal Color
Strontium Red
Copper Blue
Barium Green
Sodium YellowOrange
Calcium Orange
Gold Iron
What elements are used in fireworks to produce different
colors of light
Atomic Spectra
bull Since the electronsrsquo energy are unique for each element each element produces a unique spectra of colors when supplied energy
bull We may see with our eyes only many overlaping colors of light To see all the distinct colors in the atomrsquos spectra requires a ldquodiffraction gratingrdquo
Spectra for Neon
Each element produces a unique spectra of colored lines when viewed through a diffraction grating
Argon
Helium
Nitrogen
Mercury
Because each element produces a unique emission spectra scientists use ldquospectral analysisrdquo to determine the composition of unknown substances The spectra is like a fingerprint- absolutely unique for each element
Astronomers use ldquospectral analysisrdquo to determine the composition of stars as well
Argon
Using a Spectrometer to determine the identity of a elemental gas
1 The gas will not glow until it is energized Energy can be provided in the form of heat or by applying a high voltage The spectrum analysis power supply shown here provides high voltage
2 If you look at the glowing tube with just a diffraction grating the emission spectrum lines of color are visible
3 If you look at the glowing tube through a ldquospectrometerrdquo which contains a diffraction grating you can actually precisely measure the angles between the lines
4 Those angles allow you to precisely determine the wavelengths (or frequencies) of each of those colors
5 Since each element emits only certain wavelengths the gas can be identified
HydrogenThe emission spectrum of
Hydrogen is the most studied spectrum because it is also the simplest
Hydrogen has only ONE electron
But that ONE electron can be energized to many different orbitals ldquoexcited statesrdquo and will emit photons as it returns to its ldquoground staterdquo
Suppose an electron makes a transition from n = 3 to n = 2 What is the energy of the emitted photon
Energy = E3 ndash E2
E = 1207 eV ndash 1019 eV
E = 188 eV
What is the energy of an emitted photon if an electron makes a transition from n = 4 to n = 1
E = 1273 eVThe higher the energy of the photon the higher its frequency
E = hf
Each color has a different energy The further apart the lines the greater the difference in energy The closer the lines the less the difference in energy
Look at the spectrum for Hydrogen Which two lines have the least difference in energy Which two lines have the greatest difference in energy
Atomic SpectraAbsorption of an external source of
energy results in a transition to a higher energy level
bull A transition back to a lower level must release energy ndash in the form of a photon
bull The frequency of the emitted photon is determined by the difference in the energy levels
Ephoton = E2 ndash E1
Since E = hf the higher the energy the higher the frequency
bull Different frequencies are different colors of light or different types of EM Waves
The Hydrogen
AtomONE
electron
The frequency of the emitted photon is determined by the difference in the energy levelsEphoton = hf = E2 ndash E1
Now you try onehellipbull Get out your calculatorsbull The energized electron in Hydrogen makes a
transition from n = 3 with an energy of -15 eV down to its ground state where its energy is -136 eV
What is the frequency of the emitted photonbull Ephoton = E2 ndash E1 and Ephoton = hfbull Ephoton = -15 eV ndash (-136 eV) = 121 eVbull Ephoton = 121 eV = hf (h = 414 x 10-15 eVs )bull f = 121 eV divide 414 x 10-15 eVs = bull Frequency f = 292 x 1015 Hzbull Is this visible light Use c = f to find the
wavelengthbull wavelength = 102 x 10-7 = 102 nmbull This is NOT visible light- it is UV
Hydrogen EmissionThe energy in eV of the electron in a Hydrogen atom is given by
E =
1Find the energy of the electron at each orbit from n = 1 to n = 7
2 Find the Energy of each photon emitted (Ephoton = E) for these transitions from one orbit to another
4 to 1 5 to 2 6 to 3 7 to 4
3 to 1 4 to 2 5 to 3 6 to 4
2 to 1 3 to 2 4 to 3 5 to 4
3 Find the wavelength for each of those photons and determine what type of electromagnetic wave they are
2n
eV613
Light behaves like a wave AND like a particle
The first clear demonstration of the particle-like behavior of light was in
The Photoelectric Effect
Albert Einstein won the Nobel Prize in Physics for his study of the Photoelectric Effect
Shining light on a metal can liberate electrons from its surface
The light has to have enough energy (high enough frequency) for this effect to occur
The energy of the ldquophotoelectronsrdquo liberated from the surface depends on the frequency (the energy) of that incident light- NOT its intensity
Increasing the intensity of the light increases the number of photoelectrons emitted but not the energy of each photoelectron
When will Photoelectrons be producedPHet simulation
(Go to PHet website to explore the photoelectric effect simulation)
If no electrons are ejected you musthelliphellipincrease the frequency of the lightIf only a few electrons are ejected and you want
more your musthelliphellipincrease the intensity of the lightIf you want to increase the kinetic energy of the
electrons you musthelliphellipincrease the frequency of the light
hellip and the mathhellipUsing conservation of energyThe energy of the incident photon disappears
Where does it goFirst that energy must be used to liberate the
electron That energy is called the WORK FUNCTION WO Each kind of metal has its unique work function
Any extra energy is given appears in the electron as kinetic energy K
Photon Energy = Work function + Kinetic energy
E = Wo + K
ExamplePhoton energy = Wo + K
A photon with energy 32 eV strikes a metal surface with a work function of 18 eV What is the kinetic energy of the ejected photoelectrons
K = photon energy ndash Wo
K = 32 eV ndash 18 eV
K = 14 eV
ExamplePhoton energy = Wo + K
A photon with energy 28 eV strikes a metal surface If the kinetic energy of the ejected photoelectrons is 05 eV what is the work function of the metal
Wo = photon energy - K
Wo = 28 eV ndash 05 eV
Wo = 23 eV
hf = Wo + frac12 mv2
There is a minimum frequency called the ldquothreshold frequencyrdquo required to liberate an electron At the threshold frequency
Energy of photon = hfthreshold = Wo
That threshold photonrsquos wavelength is called the ldquocutoff wavelengthrdquo and can be found
using
c = f
Now you try some
If the cut-off wavelength for a particular metal is 320 nm what is the metalrsquos work function
First find the threshold frequency using c = f
Threshold frequency fo = 938 x 1014 Hz
Now find the work-function hfo = Wo
Be careful to use Planckrsquos constant with the correct units
h = 663 x 10-34Jmiddots or h = 414 x 10-15 eVmiddots
Wo = 622 x 10-19 J or Wo = 388 eV
What if a 450 nm light hit a surface with a work function of 236 eV What will be the kinetic energy of the photoelectron
First find the frequency of the 450 nm lightf = 667 x 1014 HzNow using conservation of energy
hf = Wo + Kinetic energySo K = hf ndash WoK = 040 eV How fast is the ejected electron movingK = frac12 mv2 m = 91 x 10-31 kg AND you have
to convert K back into Joules first
All electromagnetic photons carry energy as they travel along at ldquothe speed of lightrdquo
The energy of a photon in eV is given by
E = hf where
f is the frequency of the photon measured in Hertz
h is a constant called Plankrsquos constanth = 414 x 10-15 eVmiddots
Orh = 663 x 10-34 Jmiddots
For photonslike ldquovisible lightrdquo UV IR
microwaves etc
c = f
where c = the ldquospeed of lightrdquo
c = 3 x 108 ms
The difference frequency of electromagnetic waves (photons) determines if they are
visible light radio wave microwaves etc
higher frequency = more energy
Which photon has more energy- an X-ray photon or a microwave photon
The different frequencies of visible light correspond to different colors of light
Blue light has a higher frequency than yellow light Which color of light has the highest energy
How can you produce different colors of light
What makes one atom
different from another
The amazing colors produced in fireworks are a result of the different types of atoms that are used to make the fireworks
Each atom has its own unique number of protons neutrons and electrons
Each electron in every element is in an ldquoorbitalrdquo about the nucleus and has a unique energy
That unique energy determines the amazing colors seen in fireworks
bull A Quantum is a discreet unit of a physical quantitybull For example our money is measured in a quantum of
one cent You can have 1 cent 2 cents 8 cents etc but you canrsquot have 124 cents or 1968 cents You must jump from 1 to 2 to 3 to 4 etc
bull Electric charge which ultimately comes from either a proton or an electron is QUANTIZED
bull There is no such thing as a half of an electron or a fifth of a proton so everything that has electrical charge must have some multiple of the charge of an electron or proton- 5 electrons 8 protons etc Thatrsquos why electric charge is QUANTIZED
The electrons in their orbitals about the nucleus have QUANTIZED levels of energy that are determined by which orbital they are in
The orbitals are numbered with ldquonrdquo numbers the ldquoprinciple quantum numberrdquo
n = 1 n = 2 n = 3 etc where the orbital closest to the nucleus is n = 1
The ldquon-numberrdquo for each atomrsquos electrons determine that electronrsquos energy
The larger the ldquonrdquo the larger the energy
What does the energy of an electron in its orbital have to do with the colors of fireworks
When an electron absorbs energy from an external source in any form (heat electricity a collision etc) it jumps to a higher orbital- called an ldquoexcited staterdquo
When the electron falls back down to its original orbital called its ldquorest staterdquo or ldquoground staterdquo it must give up that extra energy The energy is emitted in the form of a photon
Some of those emitted photons are visible light of different colors- some photons are not visible to us like UV or IR or microwaves or X-rays
If an atom is continually absorbing energy all kinds of transitions between higher and lower orbital levels are possible resulting in many different types of emitted photons of many different colors
Metal Color
Strontium Red
Copper Blue
Barium Green
Sodium YellowOrange
Calcium Orange
Gold Iron
What elements are used in fireworks to produce different
colors of light
Atomic Spectra
bull Since the electronsrsquo energy are unique for each element each element produces a unique spectra of colors when supplied energy
bull We may see with our eyes only many overlaping colors of light To see all the distinct colors in the atomrsquos spectra requires a ldquodiffraction gratingrdquo
Spectra for Neon
Each element produces a unique spectra of colored lines when viewed through a diffraction grating
Argon
Helium
Nitrogen
Mercury
Because each element produces a unique emission spectra scientists use ldquospectral analysisrdquo to determine the composition of unknown substances The spectra is like a fingerprint- absolutely unique for each element
Astronomers use ldquospectral analysisrdquo to determine the composition of stars as well
Argon
Using a Spectrometer to determine the identity of a elemental gas
1 The gas will not glow until it is energized Energy can be provided in the form of heat or by applying a high voltage The spectrum analysis power supply shown here provides high voltage
2 If you look at the glowing tube with just a diffraction grating the emission spectrum lines of color are visible
3 If you look at the glowing tube through a ldquospectrometerrdquo which contains a diffraction grating you can actually precisely measure the angles between the lines
4 Those angles allow you to precisely determine the wavelengths (or frequencies) of each of those colors
5 Since each element emits only certain wavelengths the gas can be identified
HydrogenThe emission spectrum of
Hydrogen is the most studied spectrum because it is also the simplest
Hydrogen has only ONE electron
But that ONE electron can be energized to many different orbitals ldquoexcited statesrdquo and will emit photons as it returns to its ldquoground staterdquo
Suppose an electron makes a transition from n = 3 to n = 2 What is the energy of the emitted photon
Energy = E3 ndash E2
E = 1207 eV ndash 1019 eV
E = 188 eV
What is the energy of an emitted photon if an electron makes a transition from n = 4 to n = 1
E = 1273 eVThe higher the energy of the photon the higher its frequency
E = hf
Each color has a different energy The further apart the lines the greater the difference in energy The closer the lines the less the difference in energy
Look at the spectrum for Hydrogen Which two lines have the least difference in energy Which two lines have the greatest difference in energy
Atomic SpectraAbsorption of an external source of
energy results in a transition to a higher energy level
bull A transition back to a lower level must release energy ndash in the form of a photon
bull The frequency of the emitted photon is determined by the difference in the energy levels
Ephoton = E2 ndash E1
Since E = hf the higher the energy the higher the frequency
bull Different frequencies are different colors of light or different types of EM Waves
The Hydrogen
AtomONE
electron
The frequency of the emitted photon is determined by the difference in the energy levelsEphoton = hf = E2 ndash E1
Now you try onehellipbull Get out your calculatorsbull The energized electron in Hydrogen makes a
transition from n = 3 with an energy of -15 eV down to its ground state where its energy is -136 eV
What is the frequency of the emitted photonbull Ephoton = E2 ndash E1 and Ephoton = hfbull Ephoton = -15 eV ndash (-136 eV) = 121 eVbull Ephoton = 121 eV = hf (h = 414 x 10-15 eVs )bull f = 121 eV divide 414 x 10-15 eVs = bull Frequency f = 292 x 1015 Hzbull Is this visible light Use c = f to find the
wavelengthbull wavelength = 102 x 10-7 = 102 nmbull This is NOT visible light- it is UV
Hydrogen EmissionThe energy in eV of the electron in a Hydrogen atom is given by
E =
1Find the energy of the electron at each orbit from n = 1 to n = 7
2 Find the Energy of each photon emitted (Ephoton = E) for these transitions from one orbit to another
4 to 1 5 to 2 6 to 3 7 to 4
3 to 1 4 to 2 5 to 3 6 to 4
2 to 1 3 to 2 4 to 3 5 to 4
3 Find the wavelength for each of those photons and determine what type of electromagnetic wave they are
2n
eV613
Light behaves like a wave AND like a particle
The first clear demonstration of the particle-like behavior of light was in
The Photoelectric Effect
Albert Einstein won the Nobel Prize in Physics for his study of the Photoelectric Effect
Shining light on a metal can liberate electrons from its surface
The light has to have enough energy (high enough frequency) for this effect to occur
The energy of the ldquophotoelectronsrdquo liberated from the surface depends on the frequency (the energy) of that incident light- NOT its intensity
Increasing the intensity of the light increases the number of photoelectrons emitted but not the energy of each photoelectron
When will Photoelectrons be producedPHet simulation
(Go to PHet website to explore the photoelectric effect simulation)
If no electrons are ejected you musthelliphellipincrease the frequency of the lightIf only a few electrons are ejected and you want
more your musthelliphellipincrease the intensity of the lightIf you want to increase the kinetic energy of the
electrons you musthelliphellipincrease the frequency of the light
hellip and the mathhellipUsing conservation of energyThe energy of the incident photon disappears
Where does it goFirst that energy must be used to liberate the
electron That energy is called the WORK FUNCTION WO Each kind of metal has its unique work function
Any extra energy is given appears in the electron as kinetic energy K
Photon Energy = Work function + Kinetic energy
E = Wo + K
ExamplePhoton energy = Wo + K
A photon with energy 32 eV strikes a metal surface with a work function of 18 eV What is the kinetic energy of the ejected photoelectrons
K = photon energy ndash Wo
K = 32 eV ndash 18 eV
K = 14 eV
ExamplePhoton energy = Wo + K
A photon with energy 28 eV strikes a metal surface If the kinetic energy of the ejected photoelectrons is 05 eV what is the work function of the metal
Wo = photon energy - K
Wo = 28 eV ndash 05 eV
Wo = 23 eV
hf = Wo + frac12 mv2
There is a minimum frequency called the ldquothreshold frequencyrdquo required to liberate an electron At the threshold frequency
Energy of photon = hfthreshold = Wo
That threshold photonrsquos wavelength is called the ldquocutoff wavelengthrdquo and can be found
using
c = f
Now you try some
If the cut-off wavelength for a particular metal is 320 nm what is the metalrsquos work function
First find the threshold frequency using c = f
Threshold frequency fo = 938 x 1014 Hz
Now find the work-function hfo = Wo
Be careful to use Planckrsquos constant with the correct units
h = 663 x 10-34Jmiddots or h = 414 x 10-15 eVmiddots
Wo = 622 x 10-19 J or Wo = 388 eV
What if a 450 nm light hit a surface with a work function of 236 eV What will be the kinetic energy of the photoelectron
First find the frequency of the 450 nm lightf = 667 x 1014 HzNow using conservation of energy
hf = Wo + Kinetic energySo K = hf ndash WoK = 040 eV How fast is the ejected electron movingK = frac12 mv2 m = 91 x 10-31 kg AND you have
to convert K back into Joules first
For photonslike ldquovisible lightrdquo UV IR
microwaves etc
c = f
where c = the ldquospeed of lightrdquo
c = 3 x 108 ms
The difference frequency of electromagnetic waves (photons) determines if they are
visible light radio wave microwaves etc
higher frequency = more energy
Which photon has more energy- an X-ray photon or a microwave photon
The different frequencies of visible light correspond to different colors of light
Blue light has a higher frequency than yellow light Which color of light has the highest energy
How can you produce different colors of light
What makes one atom
different from another
The amazing colors produced in fireworks are a result of the different types of atoms that are used to make the fireworks
Each atom has its own unique number of protons neutrons and electrons
Each electron in every element is in an ldquoorbitalrdquo about the nucleus and has a unique energy
That unique energy determines the amazing colors seen in fireworks
bull A Quantum is a discreet unit of a physical quantitybull For example our money is measured in a quantum of
one cent You can have 1 cent 2 cents 8 cents etc but you canrsquot have 124 cents or 1968 cents You must jump from 1 to 2 to 3 to 4 etc
bull Electric charge which ultimately comes from either a proton or an electron is QUANTIZED
bull There is no such thing as a half of an electron or a fifth of a proton so everything that has electrical charge must have some multiple of the charge of an electron or proton- 5 electrons 8 protons etc Thatrsquos why electric charge is QUANTIZED
The electrons in their orbitals about the nucleus have QUANTIZED levels of energy that are determined by which orbital they are in
The orbitals are numbered with ldquonrdquo numbers the ldquoprinciple quantum numberrdquo
n = 1 n = 2 n = 3 etc where the orbital closest to the nucleus is n = 1
The ldquon-numberrdquo for each atomrsquos electrons determine that electronrsquos energy
The larger the ldquonrdquo the larger the energy
What does the energy of an electron in its orbital have to do with the colors of fireworks
When an electron absorbs energy from an external source in any form (heat electricity a collision etc) it jumps to a higher orbital- called an ldquoexcited staterdquo
When the electron falls back down to its original orbital called its ldquorest staterdquo or ldquoground staterdquo it must give up that extra energy The energy is emitted in the form of a photon
Some of those emitted photons are visible light of different colors- some photons are not visible to us like UV or IR or microwaves or X-rays
If an atom is continually absorbing energy all kinds of transitions between higher and lower orbital levels are possible resulting in many different types of emitted photons of many different colors
Metal Color
Strontium Red
Copper Blue
Barium Green
Sodium YellowOrange
Calcium Orange
Gold Iron
What elements are used in fireworks to produce different
colors of light
Atomic Spectra
bull Since the electronsrsquo energy are unique for each element each element produces a unique spectra of colors when supplied energy
bull We may see with our eyes only many overlaping colors of light To see all the distinct colors in the atomrsquos spectra requires a ldquodiffraction gratingrdquo
Spectra for Neon
Each element produces a unique spectra of colored lines when viewed through a diffraction grating
Argon
Helium
Nitrogen
Mercury
Because each element produces a unique emission spectra scientists use ldquospectral analysisrdquo to determine the composition of unknown substances The spectra is like a fingerprint- absolutely unique for each element
Astronomers use ldquospectral analysisrdquo to determine the composition of stars as well
Argon
Using a Spectrometer to determine the identity of a elemental gas
1 The gas will not glow until it is energized Energy can be provided in the form of heat or by applying a high voltage The spectrum analysis power supply shown here provides high voltage
2 If you look at the glowing tube with just a diffraction grating the emission spectrum lines of color are visible
3 If you look at the glowing tube through a ldquospectrometerrdquo which contains a diffraction grating you can actually precisely measure the angles between the lines
4 Those angles allow you to precisely determine the wavelengths (or frequencies) of each of those colors
5 Since each element emits only certain wavelengths the gas can be identified
HydrogenThe emission spectrum of
Hydrogen is the most studied spectrum because it is also the simplest
Hydrogen has only ONE electron
But that ONE electron can be energized to many different orbitals ldquoexcited statesrdquo and will emit photons as it returns to its ldquoground staterdquo
Suppose an electron makes a transition from n = 3 to n = 2 What is the energy of the emitted photon
Energy = E3 ndash E2
E = 1207 eV ndash 1019 eV
E = 188 eV
What is the energy of an emitted photon if an electron makes a transition from n = 4 to n = 1
E = 1273 eVThe higher the energy of the photon the higher its frequency
E = hf
Each color has a different energy The further apart the lines the greater the difference in energy The closer the lines the less the difference in energy
Look at the spectrum for Hydrogen Which two lines have the least difference in energy Which two lines have the greatest difference in energy
Atomic SpectraAbsorption of an external source of
energy results in a transition to a higher energy level
bull A transition back to a lower level must release energy ndash in the form of a photon
bull The frequency of the emitted photon is determined by the difference in the energy levels
Ephoton = E2 ndash E1
Since E = hf the higher the energy the higher the frequency
bull Different frequencies are different colors of light or different types of EM Waves
The Hydrogen
AtomONE
electron
The frequency of the emitted photon is determined by the difference in the energy levelsEphoton = hf = E2 ndash E1
Now you try onehellipbull Get out your calculatorsbull The energized electron in Hydrogen makes a
transition from n = 3 with an energy of -15 eV down to its ground state where its energy is -136 eV
What is the frequency of the emitted photonbull Ephoton = E2 ndash E1 and Ephoton = hfbull Ephoton = -15 eV ndash (-136 eV) = 121 eVbull Ephoton = 121 eV = hf (h = 414 x 10-15 eVs )bull f = 121 eV divide 414 x 10-15 eVs = bull Frequency f = 292 x 1015 Hzbull Is this visible light Use c = f to find the
wavelengthbull wavelength = 102 x 10-7 = 102 nmbull This is NOT visible light- it is UV
Hydrogen EmissionThe energy in eV of the electron in a Hydrogen atom is given by
E =
1Find the energy of the electron at each orbit from n = 1 to n = 7
2 Find the Energy of each photon emitted (Ephoton = E) for these transitions from one orbit to another
4 to 1 5 to 2 6 to 3 7 to 4
3 to 1 4 to 2 5 to 3 6 to 4
2 to 1 3 to 2 4 to 3 5 to 4
3 Find the wavelength for each of those photons and determine what type of electromagnetic wave they are
2n
eV613
Light behaves like a wave AND like a particle
The first clear demonstration of the particle-like behavior of light was in
The Photoelectric Effect
Albert Einstein won the Nobel Prize in Physics for his study of the Photoelectric Effect
Shining light on a metal can liberate electrons from its surface
The light has to have enough energy (high enough frequency) for this effect to occur
The energy of the ldquophotoelectronsrdquo liberated from the surface depends on the frequency (the energy) of that incident light- NOT its intensity
Increasing the intensity of the light increases the number of photoelectrons emitted but not the energy of each photoelectron
When will Photoelectrons be producedPHet simulation
(Go to PHet website to explore the photoelectric effect simulation)
If no electrons are ejected you musthelliphellipincrease the frequency of the lightIf only a few electrons are ejected and you want
more your musthelliphellipincrease the intensity of the lightIf you want to increase the kinetic energy of the
electrons you musthelliphellipincrease the frequency of the light
hellip and the mathhellipUsing conservation of energyThe energy of the incident photon disappears
Where does it goFirst that energy must be used to liberate the
electron That energy is called the WORK FUNCTION WO Each kind of metal has its unique work function
Any extra energy is given appears in the electron as kinetic energy K
Photon Energy = Work function + Kinetic energy
E = Wo + K
ExamplePhoton energy = Wo + K
A photon with energy 32 eV strikes a metal surface with a work function of 18 eV What is the kinetic energy of the ejected photoelectrons
K = photon energy ndash Wo
K = 32 eV ndash 18 eV
K = 14 eV
ExamplePhoton energy = Wo + K
A photon with energy 28 eV strikes a metal surface If the kinetic energy of the ejected photoelectrons is 05 eV what is the work function of the metal
Wo = photon energy - K
Wo = 28 eV ndash 05 eV
Wo = 23 eV
hf = Wo + frac12 mv2
There is a minimum frequency called the ldquothreshold frequencyrdquo required to liberate an electron At the threshold frequency
Energy of photon = hfthreshold = Wo
That threshold photonrsquos wavelength is called the ldquocutoff wavelengthrdquo and can be found
using
c = f
Now you try some
If the cut-off wavelength for a particular metal is 320 nm what is the metalrsquos work function
First find the threshold frequency using c = f
Threshold frequency fo = 938 x 1014 Hz
Now find the work-function hfo = Wo
Be careful to use Planckrsquos constant with the correct units
h = 663 x 10-34Jmiddots or h = 414 x 10-15 eVmiddots
Wo = 622 x 10-19 J or Wo = 388 eV
What if a 450 nm light hit a surface with a work function of 236 eV What will be the kinetic energy of the photoelectron
First find the frequency of the 450 nm lightf = 667 x 1014 HzNow using conservation of energy
hf = Wo + Kinetic energySo K = hf ndash WoK = 040 eV How fast is the ejected electron movingK = frac12 mv2 m = 91 x 10-31 kg AND you have
to convert K back into Joules first
The difference frequency of electromagnetic waves (photons) determines if they are
visible light radio wave microwaves etc
higher frequency = more energy
Which photon has more energy- an X-ray photon or a microwave photon
The different frequencies of visible light correspond to different colors of light
Blue light has a higher frequency than yellow light Which color of light has the highest energy
How can you produce different colors of light
What makes one atom
different from another
The amazing colors produced in fireworks are a result of the different types of atoms that are used to make the fireworks
Each atom has its own unique number of protons neutrons and electrons
Each electron in every element is in an ldquoorbitalrdquo about the nucleus and has a unique energy
That unique energy determines the amazing colors seen in fireworks
bull A Quantum is a discreet unit of a physical quantitybull For example our money is measured in a quantum of
one cent You can have 1 cent 2 cents 8 cents etc but you canrsquot have 124 cents or 1968 cents You must jump from 1 to 2 to 3 to 4 etc
bull Electric charge which ultimately comes from either a proton or an electron is QUANTIZED
bull There is no such thing as a half of an electron or a fifth of a proton so everything that has electrical charge must have some multiple of the charge of an electron or proton- 5 electrons 8 protons etc Thatrsquos why electric charge is QUANTIZED
The electrons in their orbitals about the nucleus have QUANTIZED levels of energy that are determined by which orbital they are in
The orbitals are numbered with ldquonrdquo numbers the ldquoprinciple quantum numberrdquo
n = 1 n = 2 n = 3 etc where the orbital closest to the nucleus is n = 1
The ldquon-numberrdquo for each atomrsquos electrons determine that electronrsquos energy
The larger the ldquonrdquo the larger the energy
What does the energy of an electron in its orbital have to do with the colors of fireworks
When an electron absorbs energy from an external source in any form (heat electricity a collision etc) it jumps to a higher orbital- called an ldquoexcited staterdquo
When the electron falls back down to its original orbital called its ldquorest staterdquo or ldquoground staterdquo it must give up that extra energy The energy is emitted in the form of a photon
Some of those emitted photons are visible light of different colors- some photons are not visible to us like UV or IR or microwaves or X-rays
If an atom is continually absorbing energy all kinds of transitions between higher and lower orbital levels are possible resulting in many different types of emitted photons of many different colors
Metal Color
Strontium Red
Copper Blue
Barium Green
Sodium YellowOrange
Calcium Orange
Gold Iron
What elements are used in fireworks to produce different
colors of light
Atomic Spectra
bull Since the electronsrsquo energy are unique for each element each element produces a unique spectra of colors when supplied energy
bull We may see with our eyes only many overlaping colors of light To see all the distinct colors in the atomrsquos spectra requires a ldquodiffraction gratingrdquo
Spectra for Neon
Each element produces a unique spectra of colored lines when viewed through a diffraction grating
Argon
Helium
Nitrogen
Mercury
Because each element produces a unique emission spectra scientists use ldquospectral analysisrdquo to determine the composition of unknown substances The spectra is like a fingerprint- absolutely unique for each element
Astronomers use ldquospectral analysisrdquo to determine the composition of stars as well
Argon
Using a Spectrometer to determine the identity of a elemental gas
1 The gas will not glow until it is energized Energy can be provided in the form of heat or by applying a high voltage The spectrum analysis power supply shown here provides high voltage
2 If you look at the glowing tube with just a diffraction grating the emission spectrum lines of color are visible
3 If you look at the glowing tube through a ldquospectrometerrdquo which contains a diffraction grating you can actually precisely measure the angles between the lines
4 Those angles allow you to precisely determine the wavelengths (or frequencies) of each of those colors
5 Since each element emits only certain wavelengths the gas can be identified
HydrogenThe emission spectrum of
Hydrogen is the most studied spectrum because it is also the simplest
Hydrogen has only ONE electron
But that ONE electron can be energized to many different orbitals ldquoexcited statesrdquo and will emit photons as it returns to its ldquoground staterdquo
Suppose an electron makes a transition from n = 3 to n = 2 What is the energy of the emitted photon
Energy = E3 ndash E2
E = 1207 eV ndash 1019 eV
E = 188 eV
What is the energy of an emitted photon if an electron makes a transition from n = 4 to n = 1
E = 1273 eVThe higher the energy of the photon the higher its frequency
E = hf
Each color has a different energy The further apart the lines the greater the difference in energy The closer the lines the less the difference in energy
Look at the spectrum for Hydrogen Which two lines have the least difference in energy Which two lines have the greatest difference in energy
Atomic SpectraAbsorption of an external source of
energy results in a transition to a higher energy level
bull A transition back to a lower level must release energy ndash in the form of a photon
bull The frequency of the emitted photon is determined by the difference in the energy levels
Ephoton = E2 ndash E1
Since E = hf the higher the energy the higher the frequency
bull Different frequencies are different colors of light or different types of EM Waves
The Hydrogen
AtomONE
electron
The frequency of the emitted photon is determined by the difference in the energy levelsEphoton = hf = E2 ndash E1
Now you try onehellipbull Get out your calculatorsbull The energized electron in Hydrogen makes a
transition from n = 3 with an energy of -15 eV down to its ground state where its energy is -136 eV
What is the frequency of the emitted photonbull Ephoton = E2 ndash E1 and Ephoton = hfbull Ephoton = -15 eV ndash (-136 eV) = 121 eVbull Ephoton = 121 eV = hf (h = 414 x 10-15 eVs )bull f = 121 eV divide 414 x 10-15 eVs = bull Frequency f = 292 x 1015 Hzbull Is this visible light Use c = f to find the
wavelengthbull wavelength = 102 x 10-7 = 102 nmbull This is NOT visible light- it is UV
Hydrogen EmissionThe energy in eV of the electron in a Hydrogen atom is given by
E =
1Find the energy of the electron at each orbit from n = 1 to n = 7
2 Find the Energy of each photon emitted (Ephoton = E) for these transitions from one orbit to another
4 to 1 5 to 2 6 to 3 7 to 4
3 to 1 4 to 2 5 to 3 6 to 4
2 to 1 3 to 2 4 to 3 5 to 4
3 Find the wavelength for each of those photons and determine what type of electromagnetic wave they are
2n
eV613
Light behaves like a wave AND like a particle
The first clear demonstration of the particle-like behavior of light was in
The Photoelectric Effect
Albert Einstein won the Nobel Prize in Physics for his study of the Photoelectric Effect
Shining light on a metal can liberate electrons from its surface
The light has to have enough energy (high enough frequency) for this effect to occur
The energy of the ldquophotoelectronsrdquo liberated from the surface depends on the frequency (the energy) of that incident light- NOT its intensity
Increasing the intensity of the light increases the number of photoelectrons emitted but not the energy of each photoelectron
When will Photoelectrons be producedPHet simulation
(Go to PHet website to explore the photoelectric effect simulation)
If no electrons are ejected you musthelliphellipincrease the frequency of the lightIf only a few electrons are ejected and you want
more your musthelliphellipincrease the intensity of the lightIf you want to increase the kinetic energy of the
electrons you musthelliphellipincrease the frequency of the light
hellip and the mathhellipUsing conservation of energyThe energy of the incident photon disappears
Where does it goFirst that energy must be used to liberate the
electron That energy is called the WORK FUNCTION WO Each kind of metal has its unique work function
Any extra energy is given appears in the electron as kinetic energy K
Photon Energy = Work function + Kinetic energy
E = Wo + K
ExamplePhoton energy = Wo + K
A photon with energy 32 eV strikes a metal surface with a work function of 18 eV What is the kinetic energy of the ejected photoelectrons
K = photon energy ndash Wo
K = 32 eV ndash 18 eV
K = 14 eV
ExamplePhoton energy = Wo + K
A photon with energy 28 eV strikes a metal surface If the kinetic energy of the ejected photoelectrons is 05 eV what is the work function of the metal
Wo = photon energy - K
Wo = 28 eV ndash 05 eV
Wo = 23 eV
hf = Wo + frac12 mv2
There is a minimum frequency called the ldquothreshold frequencyrdquo required to liberate an electron At the threshold frequency
Energy of photon = hfthreshold = Wo
That threshold photonrsquos wavelength is called the ldquocutoff wavelengthrdquo and can be found
using
c = f
Now you try some
If the cut-off wavelength for a particular metal is 320 nm what is the metalrsquos work function
First find the threshold frequency using c = f
Threshold frequency fo = 938 x 1014 Hz
Now find the work-function hfo = Wo
Be careful to use Planckrsquos constant with the correct units
h = 663 x 10-34Jmiddots or h = 414 x 10-15 eVmiddots
Wo = 622 x 10-19 J or Wo = 388 eV
What if a 450 nm light hit a surface with a work function of 236 eV What will be the kinetic energy of the photoelectron
First find the frequency of the 450 nm lightf = 667 x 1014 HzNow using conservation of energy
hf = Wo + Kinetic energySo K = hf ndash WoK = 040 eV How fast is the ejected electron movingK = frac12 mv2 m = 91 x 10-31 kg AND you have
to convert K back into Joules first
Which photon has more energy- an X-ray photon or a microwave photon
The different frequencies of visible light correspond to different colors of light
Blue light has a higher frequency than yellow light Which color of light has the highest energy
How can you produce different colors of light
What makes one atom
different from another
The amazing colors produced in fireworks are a result of the different types of atoms that are used to make the fireworks
Each atom has its own unique number of protons neutrons and electrons
Each electron in every element is in an ldquoorbitalrdquo about the nucleus and has a unique energy
That unique energy determines the amazing colors seen in fireworks
bull A Quantum is a discreet unit of a physical quantitybull For example our money is measured in a quantum of
one cent You can have 1 cent 2 cents 8 cents etc but you canrsquot have 124 cents or 1968 cents You must jump from 1 to 2 to 3 to 4 etc
bull Electric charge which ultimately comes from either a proton or an electron is QUANTIZED
bull There is no such thing as a half of an electron or a fifth of a proton so everything that has electrical charge must have some multiple of the charge of an electron or proton- 5 electrons 8 protons etc Thatrsquos why electric charge is QUANTIZED
The electrons in their orbitals about the nucleus have QUANTIZED levels of energy that are determined by which orbital they are in
The orbitals are numbered with ldquonrdquo numbers the ldquoprinciple quantum numberrdquo
n = 1 n = 2 n = 3 etc where the orbital closest to the nucleus is n = 1
The ldquon-numberrdquo for each atomrsquos electrons determine that electronrsquos energy
The larger the ldquonrdquo the larger the energy
What does the energy of an electron in its orbital have to do with the colors of fireworks
When an electron absorbs energy from an external source in any form (heat electricity a collision etc) it jumps to a higher orbital- called an ldquoexcited staterdquo
When the electron falls back down to its original orbital called its ldquorest staterdquo or ldquoground staterdquo it must give up that extra energy The energy is emitted in the form of a photon
Some of those emitted photons are visible light of different colors- some photons are not visible to us like UV or IR or microwaves or X-rays
If an atom is continually absorbing energy all kinds of transitions between higher and lower orbital levels are possible resulting in many different types of emitted photons of many different colors
Metal Color
Strontium Red
Copper Blue
Barium Green
Sodium YellowOrange
Calcium Orange
Gold Iron
What elements are used in fireworks to produce different
colors of light
Atomic Spectra
bull Since the electronsrsquo energy are unique for each element each element produces a unique spectra of colors when supplied energy
bull We may see with our eyes only many overlaping colors of light To see all the distinct colors in the atomrsquos spectra requires a ldquodiffraction gratingrdquo
Spectra for Neon
Each element produces a unique spectra of colored lines when viewed through a diffraction grating
Argon
Helium
Nitrogen
Mercury
Because each element produces a unique emission spectra scientists use ldquospectral analysisrdquo to determine the composition of unknown substances The spectra is like a fingerprint- absolutely unique for each element
Astronomers use ldquospectral analysisrdquo to determine the composition of stars as well
Argon
Using a Spectrometer to determine the identity of a elemental gas
1 The gas will not glow until it is energized Energy can be provided in the form of heat or by applying a high voltage The spectrum analysis power supply shown here provides high voltage
2 If you look at the glowing tube with just a diffraction grating the emission spectrum lines of color are visible
3 If you look at the glowing tube through a ldquospectrometerrdquo which contains a diffraction grating you can actually precisely measure the angles between the lines
4 Those angles allow you to precisely determine the wavelengths (or frequencies) of each of those colors
5 Since each element emits only certain wavelengths the gas can be identified
HydrogenThe emission spectrum of
Hydrogen is the most studied spectrum because it is also the simplest
Hydrogen has only ONE electron
But that ONE electron can be energized to many different orbitals ldquoexcited statesrdquo and will emit photons as it returns to its ldquoground staterdquo
Suppose an electron makes a transition from n = 3 to n = 2 What is the energy of the emitted photon
Energy = E3 ndash E2
E = 1207 eV ndash 1019 eV
E = 188 eV
What is the energy of an emitted photon if an electron makes a transition from n = 4 to n = 1
E = 1273 eVThe higher the energy of the photon the higher its frequency
E = hf
Each color has a different energy The further apart the lines the greater the difference in energy The closer the lines the less the difference in energy
Look at the spectrum for Hydrogen Which two lines have the least difference in energy Which two lines have the greatest difference in energy
Atomic SpectraAbsorption of an external source of
energy results in a transition to a higher energy level
bull A transition back to a lower level must release energy ndash in the form of a photon
bull The frequency of the emitted photon is determined by the difference in the energy levels
Ephoton = E2 ndash E1
Since E = hf the higher the energy the higher the frequency
bull Different frequencies are different colors of light or different types of EM Waves
The Hydrogen
AtomONE
electron
The frequency of the emitted photon is determined by the difference in the energy levelsEphoton = hf = E2 ndash E1
Now you try onehellipbull Get out your calculatorsbull The energized electron in Hydrogen makes a
transition from n = 3 with an energy of -15 eV down to its ground state where its energy is -136 eV
What is the frequency of the emitted photonbull Ephoton = E2 ndash E1 and Ephoton = hfbull Ephoton = -15 eV ndash (-136 eV) = 121 eVbull Ephoton = 121 eV = hf (h = 414 x 10-15 eVs )bull f = 121 eV divide 414 x 10-15 eVs = bull Frequency f = 292 x 1015 Hzbull Is this visible light Use c = f to find the
wavelengthbull wavelength = 102 x 10-7 = 102 nmbull This is NOT visible light- it is UV
Hydrogen EmissionThe energy in eV of the electron in a Hydrogen atom is given by
E =
1Find the energy of the electron at each orbit from n = 1 to n = 7
2 Find the Energy of each photon emitted (Ephoton = E) for these transitions from one orbit to another
4 to 1 5 to 2 6 to 3 7 to 4
3 to 1 4 to 2 5 to 3 6 to 4
2 to 1 3 to 2 4 to 3 5 to 4
3 Find the wavelength for each of those photons and determine what type of electromagnetic wave they are
2n
eV613
Light behaves like a wave AND like a particle
The first clear demonstration of the particle-like behavior of light was in
The Photoelectric Effect
Albert Einstein won the Nobel Prize in Physics for his study of the Photoelectric Effect
Shining light on a metal can liberate electrons from its surface
The light has to have enough energy (high enough frequency) for this effect to occur
The energy of the ldquophotoelectronsrdquo liberated from the surface depends on the frequency (the energy) of that incident light- NOT its intensity
Increasing the intensity of the light increases the number of photoelectrons emitted but not the energy of each photoelectron
When will Photoelectrons be producedPHet simulation
(Go to PHet website to explore the photoelectric effect simulation)
If no electrons are ejected you musthelliphellipincrease the frequency of the lightIf only a few electrons are ejected and you want
more your musthelliphellipincrease the intensity of the lightIf you want to increase the kinetic energy of the
electrons you musthelliphellipincrease the frequency of the light
hellip and the mathhellipUsing conservation of energyThe energy of the incident photon disappears
Where does it goFirst that energy must be used to liberate the
electron That energy is called the WORK FUNCTION WO Each kind of metal has its unique work function
Any extra energy is given appears in the electron as kinetic energy K
Photon Energy = Work function + Kinetic energy
E = Wo + K
ExamplePhoton energy = Wo + K
A photon with energy 32 eV strikes a metal surface with a work function of 18 eV What is the kinetic energy of the ejected photoelectrons
K = photon energy ndash Wo
K = 32 eV ndash 18 eV
K = 14 eV
ExamplePhoton energy = Wo + K
A photon with energy 28 eV strikes a metal surface If the kinetic energy of the ejected photoelectrons is 05 eV what is the work function of the metal
Wo = photon energy - K
Wo = 28 eV ndash 05 eV
Wo = 23 eV
hf = Wo + frac12 mv2
There is a minimum frequency called the ldquothreshold frequencyrdquo required to liberate an electron At the threshold frequency
Energy of photon = hfthreshold = Wo
That threshold photonrsquos wavelength is called the ldquocutoff wavelengthrdquo and can be found
using
c = f
Now you try some
If the cut-off wavelength for a particular metal is 320 nm what is the metalrsquos work function
First find the threshold frequency using c = f
Threshold frequency fo = 938 x 1014 Hz
Now find the work-function hfo = Wo
Be careful to use Planckrsquos constant with the correct units
h = 663 x 10-34Jmiddots or h = 414 x 10-15 eVmiddots
Wo = 622 x 10-19 J or Wo = 388 eV
What if a 450 nm light hit a surface with a work function of 236 eV What will be the kinetic energy of the photoelectron
First find the frequency of the 450 nm lightf = 667 x 1014 HzNow using conservation of energy
hf = Wo + Kinetic energySo K = hf ndash WoK = 040 eV How fast is the ejected electron movingK = frac12 mv2 m = 91 x 10-31 kg AND you have
to convert K back into Joules first
The different frequencies of visible light correspond to different colors of light
Blue light has a higher frequency than yellow light Which color of light has the highest energy
How can you produce different colors of light
What makes one atom
different from another
The amazing colors produced in fireworks are a result of the different types of atoms that are used to make the fireworks
Each atom has its own unique number of protons neutrons and electrons
Each electron in every element is in an ldquoorbitalrdquo about the nucleus and has a unique energy
That unique energy determines the amazing colors seen in fireworks
bull A Quantum is a discreet unit of a physical quantitybull For example our money is measured in a quantum of
one cent You can have 1 cent 2 cents 8 cents etc but you canrsquot have 124 cents or 1968 cents You must jump from 1 to 2 to 3 to 4 etc
bull Electric charge which ultimately comes from either a proton or an electron is QUANTIZED
bull There is no such thing as a half of an electron or a fifth of a proton so everything that has electrical charge must have some multiple of the charge of an electron or proton- 5 electrons 8 protons etc Thatrsquos why electric charge is QUANTIZED
The electrons in their orbitals about the nucleus have QUANTIZED levels of energy that are determined by which orbital they are in
The orbitals are numbered with ldquonrdquo numbers the ldquoprinciple quantum numberrdquo
n = 1 n = 2 n = 3 etc where the orbital closest to the nucleus is n = 1
The ldquon-numberrdquo for each atomrsquos electrons determine that electronrsquos energy
The larger the ldquonrdquo the larger the energy
What does the energy of an electron in its orbital have to do with the colors of fireworks
When an electron absorbs energy from an external source in any form (heat electricity a collision etc) it jumps to a higher orbital- called an ldquoexcited staterdquo
When the electron falls back down to its original orbital called its ldquorest staterdquo or ldquoground staterdquo it must give up that extra energy The energy is emitted in the form of a photon
Some of those emitted photons are visible light of different colors- some photons are not visible to us like UV or IR or microwaves or X-rays
If an atom is continually absorbing energy all kinds of transitions between higher and lower orbital levels are possible resulting in many different types of emitted photons of many different colors
Metal Color
Strontium Red
Copper Blue
Barium Green
Sodium YellowOrange
Calcium Orange
Gold Iron
What elements are used in fireworks to produce different
colors of light
Atomic Spectra
bull Since the electronsrsquo energy are unique for each element each element produces a unique spectra of colors when supplied energy
bull We may see with our eyes only many overlaping colors of light To see all the distinct colors in the atomrsquos spectra requires a ldquodiffraction gratingrdquo
Spectra for Neon
Each element produces a unique spectra of colored lines when viewed through a diffraction grating
Argon
Helium
Nitrogen
Mercury
Because each element produces a unique emission spectra scientists use ldquospectral analysisrdquo to determine the composition of unknown substances The spectra is like a fingerprint- absolutely unique for each element
Astronomers use ldquospectral analysisrdquo to determine the composition of stars as well
Argon
Using a Spectrometer to determine the identity of a elemental gas
1 The gas will not glow until it is energized Energy can be provided in the form of heat or by applying a high voltage The spectrum analysis power supply shown here provides high voltage
2 If you look at the glowing tube with just a diffraction grating the emission spectrum lines of color are visible
3 If you look at the glowing tube through a ldquospectrometerrdquo which contains a diffraction grating you can actually precisely measure the angles between the lines
4 Those angles allow you to precisely determine the wavelengths (or frequencies) of each of those colors
5 Since each element emits only certain wavelengths the gas can be identified
HydrogenThe emission spectrum of
Hydrogen is the most studied spectrum because it is also the simplest
Hydrogen has only ONE electron
But that ONE electron can be energized to many different orbitals ldquoexcited statesrdquo and will emit photons as it returns to its ldquoground staterdquo
Suppose an electron makes a transition from n = 3 to n = 2 What is the energy of the emitted photon
Energy = E3 ndash E2
E = 1207 eV ndash 1019 eV
E = 188 eV
What is the energy of an emitted photon if an electron makes a transition from n = 4 to n = 1
E = 1273 eVThe higher the energy of the photon the higher its frequency
E = hf
Each color has a different energy The further apart the lines the greater the difference in energy The closer the lines the less the difference in energy
Look at the spectrum for Hydrogen Which two lines have the least difference in energy Which two lines have the greatest difference in energy
Atomic SpectraAbsorption of an external source of
energy results in a transition to a higher energy level
bull A transition back to a lower level must release energy ndash in the form of a photon
bull The frequency of the emitted photon is determined by the difference in the energy levels
Ephoton = E2 ndash E1
Since E = hf the higher the energy the higher the frequency
bull Different frequencies are different colors of light or different types of EM Waves
The Hydrogen
AtomONE
electron
The frequency of the emitted photon is determined by the difference in the energy levelsEphoton = hf = E2 ndash E1
Now you try onehellipbull Get out your calculatorsbull The energized electron in Hydrogen makes a
transition from n = 3 with an energy of -15 eV down to its ground state where its energy is -136 eV
What is the frequency of the emitted photonbull Ephoton = E2 ndash E1 and Ephoton = hfbull Ephoton = -15 eV ndash (-136 eV) = 121 eVbull Ephoton = 121 eV = hf (h = 414 x 10-15 eVs )bull f = 121 eV divide 414 x 10-15 eVs = bull Frequency f = 292 x 1015 Hzbull Is this visible light Use c = f to find the
wavelengthbull wavelength = 102 x 10-7 = 102 nmbull This is NOT visible light- it is UV
Hydrogen EmissionThe energy in eV of the electron in a Hydrogen atom is given by
E =
1Find the energy of the electron at each orbit from n = 1 to n = 7
2 Find the Energy of each photon emitted (Ephoton = E) for these transitions from one orbit to another
4 to 1 5 to 2 6 to 3 7 to 4
3 to 1 4 to 2 5 to 3 6 to 4
2 to 1 3 to 2 4 to 3 5 to 4
3 Find the wavelength for each of those photons and determine what type of electromagnetic wave they are
2n
eV613
Light behaves like a wave AND like a particle
The first clear demonstration of the particle-like behavior of light was in
The Photoelectric Effect
Albert Einstein won the Nobel Prize in Physics for his study of the Photoelectric Effect
Shining light on a metal can liberate electrons from its surface
The light has to have enough energy (high enough frequency) for this effect to occur
The energy of the ldquophotoelectronsrdquo liberated from the surface depends on the frequency (the energy) of that incident light- NOT its intensity
Increasing the intensity of the light increases the number of photoelectrons emitted but not the energy of each photoelectron
When will Photoelectrons be producedPHet simulation
(Go to PHet website to explore the photoelectric effect simulation)
If no electrons are ejected you musthelliphellipincrease the frequency of the lightIf only a few electrons are ejected and you want
more your musthelliphellipincrease the intensity of the lightIf you want to increase the kinetic energy of the
electrons you musthelliphellipincrease the frequency of the light
hellip and the mathhellipUsing conservation of energyThe energy of the incident photon disappears
Where does it goFirst that energy must be used to liberate the
electron That energy is called the WORK FUNCTION WO Each kind of metal has its unique work function
Any extra energy is given appears in the electron as kinetic energy K
Photon Energy = Work function + Kinetic energy
E = Wo + K
ExamplePhoton energy = Wo + K
A photon with energy 32 eV strikes a metal surface with a work function of 18 eV What is the kinetic energy of the ejected photoelectrons
K = photon energy ndash Wo
K = 32 eV ndash 18 eV
K = 14 eV
ExamplePhoton energy = Wo + K
A photon with energy 28 eV strikes a metal surface If the kinetic energy of the ejected photoelectrons is 05 eV what is the work function of the metal
Wo = photon energy - K
Wo = 28 eV ndash 05 eV
Wo = 23 eV
hf = Wo + frac12 mv2
There is a minimum frequency called the ldquothreshold frequencyrdquo required to liberate an electron At the threshold frequency
Energy of photon = hfthreshold = Wo
That threshold photonrsquos wavelength is called the ldquocutoff wavelengthrdquo and can be found
using
c = f
Now you try some
If the cut-off wavelength for a particular metal is 320 nm what is the metalrsquos work function
First find the threshold frequency using c = f
Threshold frequency fo = 938 x 1014 Hz
Now find the work-function hfo = Wo
Be careful to use Planckrsquos constant with the correct units
h = 663 x 10-34Jmiddots or h = 414 x 10-15 eVmiddots
Wo = 622 x 10-19 J or Wo = 388 eV
What if a 450 nm light hit a surface with a work function of 236 eV What will be the kinetic energy of the photoelectron
First find the frequency of the 450 nm lightf = 667 x 1014 HzNow using conservation of energy
hf = Wo + Kinetic energySo K = hf ndash WoK = 040 eV How fast is the ejected electron movingK = frac12 mv2 m = 91 x 10-31 kg AND you have
to convert K back into Joules first
How can you produce different colors of light
What makes one atom
different from another
The amazing colors produced in fireworks are a result of the different types of atoms that are used to make the fireworks
Each atom has its own unique number of protons neutrons and electrons
Each electron in every element is in an ldquoorbitalrdquo about the nucleus and has a unique energy
That unique energy determines the amazing colors seen in fireworks
bull A Quantum is a discreet unit of a physical quantitybull For example our money is measured in a quantum of
one cent You can have 1 cent 2 cents 8 cents etc but you canrsquot have 124 cents or 1968 cents You must jump from 1 to 2 to 3 to 4 etc
bull Electric charge which ultimately comes from either a proton or an electron is QUANTIZED
bull There is no such thing as a half of an electron or a fifth of a proton so everything that has electrical charge must have some multiple of the charge of an electron or proton- 5 electrons 8 protons etc Thatrsquos why electric charge is QUANTIZED
The electrons in their orbitals about the nucleus have QUANTIZED levels of energy that are determined by which orbital they are in
The orbitals are numbered with ldquonrdquo numbers the ldquoprinciple quantum numberrdquo
n = 1 n = 2 n = 3 etc where the orbital closest to the nucleus is n = 1
The ldquon-numberrdquo for each atomrsquos electrons determine that electronrsquos energy
The larger the ldquonrdquo the larger the energy
What does the energy of an electron in its orbital have to do with the colors of fireworks
When an electron absorbs energy from an external source in any form (heat electricity a collision etc) it jumps to a higher orbital- called an ldquoexcited staterdquo
When the electron falls back down to its original orbital called its ldquorest staterdquo or ldquoground staterdquo it must give up that extra energy The energy is emitted in the form of a photon
Some of those emitted photons are visible light of different colors- some photons are not visible to us like UV or IR or microwaves or X-rays
If an atom is continually absorbing energy all kinds of transitions between higher and lower orbital levels are possible resulting in many different types of emitted photons of many different colors
Metal Color
Strontium Red
Copper Blue
Barium Green
Sodium YellowOrange
Calcium Orange
Gold Iron
What elements are used in fireworks to produce different
colors of light
Atomic Spectra
bull Since the electronsrsquo energy are unique for each element each element produces a unique spectra of colors when supplied energy
bull We may see with our eyes only many overlaping colors of light To see all the distinct colors in the atomrsquos spectra requires a ldquodiffraction gratingrdquo
Spectra for Neon
Each element produces a unique spectra of colored lines when viewed through a diffraction grating
Argon
Helium
Nitrogen
Mercury
Because each element produces a unique emission spectra scientists use ldquospectral analysisrdquo to determine the composition of unknown substances The spectra is like a fingerprint- absolutely unique for each element
Astronomers use ldquospectral analysisrdquo to determine the composition of stars as well
Argon
Using a Spectrometer to determine the identity of a elemental gas
1 The gas will not glow until it is energized Energy can be provided in the form of heat or by applying a high voltage The spectrum analysis power supply shown here provides high voltage
2 If you look at the glowing tube with just a diffraction grating the emission spectrum lines of color are visible
3 If you look at the glowing tube through a ldquospectrometerrdquo which contains a diffraction grating you can actually precisely measure the angles between the lines
4 Those angles allow you to precisely determine the wavelengths (or frequencies) of each of those colors
5 Since each element emits only certain wavelengths the gas can be identified
HydrogenThe emission spectrum of
Hydrogen is the most studied spectrum because it is also the simplest
Hydrogen has only ONE electron
But that ONE electron can be energized to many different orbitals ldquoexcited statesrdquo and will emit photons as it returns to its ldquoground staterdquo
Suppose an electron makes a transition from n = 3 to n = 2 What is the energy of the emitted photon
Energy = E3 ndash E2
E = 1207 eV ndash 1019 eV
E = 188 eV
What is the energy of an emitted photon if an electron makes a transition from n = 4 to n = 1
E = 1273 eVThe higher the energy of the photon the higher its frequency
E = hf
Each color has a different energy The further apart the lines the greater the difference in energy The closer the lines the less the difference in energy
Look at the spectrum for Hydrogen Which two lines have the least difference in energy Which two lines have the greatest difference in energy
Atomic SpectraAbsorption of an external source of
energy results in a transition to a higher energy level
bull A transition back to a lower level must release energy ndash in the form of a photon
bull The frequency of the emitted photon is determined by the difference in the energy levels
Ephoton = E2 ndash E1
Since E = hf the higher the energy the higher the frequency
bull Different frequencies are different colors of light or different types of EM Waves
The Hydrogen
AtomONE
electron
The frequency of the emitted photon is determined by the difference in the energy levelsEphoton = hf = E2 ndash E1
Now you try onehellipbull Get out your calculatorsbull The energized electron in Hydrogen makes a
transition from n = 3 with an energy of -15 eV down to its ground state where its energy is -136 eV
What is the frequency of the emitted photonbull Ephoton = E2 ndash E1 and Ephoton = hfbull Ephoton = -15 eV ndash (-136 eV) = 121 eVbull Ephoton = 121 eV = hf (h = 414 x 10-15 eVs )bull f = 121 eV divide 414 x 10-15 eVs = bull Frequency f = 292 x 1015 Hzbull Is this visible light Use c = f to find the
wavelengthbull wavelength = 102 x 10-7 = 102 nmbull This is NOT visible light- it is UV
Hydrogen EmissionThe energy in eV of the electron in a Hydrogen atom is given by
E =
1Find the energy of the electron at each orbit from n = 1 to n = 7
2 Find the Energy of each photon emitted (Ephoton = E) for these transitions from one orbit to another
4 to 1 5 to 2 6 to 3 7 to 4
3 to 1 4 to 2 5 to 3 6 to 4
2 to 1 3 to 2 4 to 3 5 to 4
3 Find the wavelength for each of those photons and determine what type of electromagnetic wave they are
2n
eV613
Light behaves like a wave AND like a particle
The first clear demonstration of the particle-like behavior of light was in
The Photoelectric Effect
Albert Einstein won the Nobel Prize in Physics for his study of the Photoelectric Effect
Shining light on a metal can liberate electrons from its surface
The light has to have enough energy (high enough frequency) for this effect to occur
The energy of the ldquophotoelectronsrdquo liberated from the surface depends on the frequency (the energy) of that incident light- NOT its intensity
Increasing the intensity of the light increases the number of photoelectrons emitted but not the energy of each photoelectron
When will Photoelectrons be producedPHet simulation
(Go to PHet website to explore the photoelectric effect simulation)
If no electrons are ejected you musthelliphellipincrease the frequency of the lightIf only a few electrons are ejected and you want
more your musthelliphellipincrease the intensity of the lightIf you want to increase the kinetic energy of the
electrons you musthelliphellipincrease the frequency of the light
hellip and the mathhellipUsing conservation of energyThe energy of the incident photon disappears
Where does it goFirst that energy must be used to liberate the
electron That energy is called the WORK FUNCTION WO Each kind of metal has its unique work function
Any extra energy is given appears in the electron as kinetic energy K
Photon Energy = Work function + Kinetic energy
E = Wo + K
ExamplePhoton energy = Wo + K
A photon with energy 32 eV strikes a metal surface with a work function of 18 eV What is the kinetic energy of the ejected photoelectrons
K = photon energy ndash Wo
K = 32 eV ndash 18 eV
K = 14 eV
ExamplePhoton energy = Wo + K
A photon with energy 28 eV strikes a metal surface If the kinetic energy of the ejected photoelectrons is 05 eV what is the work function of the metal
Wo = photon energy - K
Wo = 28 eV ndash 05 eV
Wo = 23 eV
hf = Wo + frac12 mv2
There is a minimum frequency called the ldquothreshold frequencyrdquo required to liberate an electron At the threshold frequency
Energy of photon = hfthreshold = Wo
That threshold photonrsquos wavelength is called the ldquocutoff wavelengthrdquo and can be found
using
c = f
Now you try some
If the cut-off wavelength for a particular metal is 320 nm what is the metalrsquos work function
First find the threshold frequency using c = f
Threshold frequency fo = 938 x 1014 Hz
Now find the work-function hfo = Wo
Be careful to use Planckrsquos constant with the correct units
h = 663 x 10-34Jmiddots or h = 414 x 10-15 eVmiddots
Wo = 622 x 10-19 J or Wo = 388 eV
What if a 450 nm light hit a surface with a work function of 236 eV What will be the kinetic energy of the photoelectron
First find the frequency of the 450 nm lightf = 667 x 1014 HzNow using conservation of energy
hf = Wo + Kinetic energySo K = hf ndash WoK = 040 eV How fast is the ejected electron movingK = frac12 mv2 m = 91 x 10-31 kg AND you have
to convert K back into Joules first
What makes one atom
different from another
The amazing colors produced in fireworks are a result of the different types of atoms that are used to make the fireworks
Each atom has its own unique number of protons neutrons and electrons
Each electron in every element is in an ldquoorbitalrdquo about the nucleus and has a unique energy
That unique energy determines the amazing colors seen in fireworks
bull A Quantum is a discreet unit of a physical quantitybull For example our money is measured in a quantum of
one cent You can have 1 cent 2 cents 8 cents etc but you canrsquot have 124 cents or 1968 cents You must jump from 1 to 2 to 3 to 4 etc
bull Electric charge which ultimately comes from either a proton or an electron is QUANTIZED
bull There is no such thing as a half of an electron or a fifth of a proton so everything that has electrical charge must have some multiple of the charge of an electron or proton- 5 electrons 8 protons etc Thatrsquos why electric charge is QUANTIZED
The electrons in their orbitals about the nucleus have QUANTIZED levels of energy that are determined by which orbital they are in
The orbitals are numbered with ldquonrdquo numbers the ldquoprinciple quantum numberrdquo
n = 1 n = 2 n = 3 etc where the orbital closest to the nucleus is n = 1
The ldquon-numberrdquo for each atomrsquos electrons determine that electronrsquos energy
The larger the ldquonrdquo the larger the energy
What does the energy of an electron in its orbital have to do with the colors of fireworks
When an electron absorbs energy from an external source in any form (heat electricity a collision etc) it jumps to a higher orbital- called an ldquoexcited staterdquo
When the electron falls back down to its original orbital called its ldquorest staterdquo or ldquoground staterdquo it must give up that extra energy The energy is emitted in the form of a photon
Some of those emitted photons are visible light of different colors- some photons are not visible to us like UV or IR or microwaves or X-rays
If an atom is continually absorbing energy all kinds of transitions between higher and lower orbital levels are possible resulting in many different types of emitted photons of many different colors
Metal Color
Strontium Red
Copper Blue
Barium Green
Sodium YellowOrange
Calcium Orange
Gold Iron
What elements are used in fireworks to produce different
colors of light
Atomic Spectra
bull Since the electronsrsquo energy are unique for each element each element produces a unique spectra of colors when supplied energy
bull We may see with our eyes only many overlaping colors of light To see all the distinct colors in the atomrsquos spectra requires a ldquodiffraction gratingrdquo
Spectra for Neon
Each element produces a unique spectra of colored lines when viewed through a diffraction grating
Argon
Helium
Nitrogen
Mercury
Because each element produces a unique emission spectra scientists use ldquospectral analysisrdquo to determine the composition of unknown substances The spectra is like a fingerprint- absolutely unique for each element
Astronomers use ldquospectral analysisrdquo to determine the composition of stars as well
Argon
Using a Spectrometer to determine the identity of a elemental gas
1 The gas will not glow until it is energized Energy can be provided in the form of heat or by applying a high voltage The spectrum analysis power supply shown here provides high voltage
2 If you look at the glowing tube with just a diffraction grating the emission spectrum lines of color are visible
3 If you look at the glowing tube through a ldquospectrometerrdquo which contains a diffraction grating you can actually precisely measure the angles between the lines
4 Those angles allow you to precisely determine the wavelengths (or frequencies) of each of those colors
5 Since each element emits only certain wavelengths the gas can be identified
HydrogenThe emission spectrum of
Hydrogen is the most studied spectrum because it is also the simplest
Hydrogen has only ONE electron
But that ONE electron can be energized to many different orbitals ldquoexcited statesrdquo and will emit photons as it returns to its ldquoground staterdquo
Suppose an electron makes a transition from n = 3 to n = 2 What is the energy of the emitted photon
Energy = E3 ndash E2
E = 1207 eV ndash 1019 eV
E = 188 eV
What is the energy of an emitted photon if an electron makes a transition from n = 4 to n = 1
E = 1273 eVThe higher the energy of the photon the higher its frequency
E = hf
Each color has a different energy The further apart the lines the greater the difference in energy The closer the lines the less the difference in energy
Look at the spectrum for Hydrogen Which two lines have the least difference in energy Which two lines have the greatest difference in energy
Atomic SpectraAbsorption of an external source of
energy results in a transition to a higher energy level
bull A transition back to a lower level must release energy ndash in the form of a photon
bull The frequency of the emitted photon is determined by the difference in the energy levels
Ephoton = E2 ndash E1
Since E = hf the higher the energy the higher the frequency
bull Different frequencies are different colors of light or different types of EM Waves
The Hydrogen
AtomONE
electron
The frequency of the emitted photon is determined by the difference in the energy levelsEphoton = hf = E2 ndash E1
Now you try onehellipbull Get out your calculatorsbull The energized electron in Hydrogen makes a
transition from n = 3 with an energy of -15 eV down to its ground state where its energy is -136 eV
What is the frequency of the emitted photonbull Ephoton = E2 ndash E1 and Ephoton = hfbull Ephoton = -15 eV ndash (-136 eV) = 121 eVbull Ephoton = 121 eV = hf (h = 414 x 10-15 eVs )bull f = 121 eV divide 414 x 10-15 eVs = bull Frequency f = 292 x 1015 Hzbull Is this visible light Use c = f to find the
wavelengthbull wavelength = 102 x 10-7 = 102 nmbull This is NOT visible light- it is UV
Hydrogen EmissionThe energy in eV of the electron in a Hydrogen atom is given by
E =
1Find the energy of the electron at each orbit from n = 1 to n = 7
2 Find the Energy of each photon emitted (Ephoton = E) for these transitions from one orbit to another
4 to 1 5 to 2 6 to 3 7 to 4
3 to 1 4 to 2 5 to 3 6 to 4
2 to 1 3 to 2 4 to 3 5 to 4
3 Find the wavelength for each of those photons and determine what type of electromagnetic wave they are
2n
eV613
Light behaves like a wave AND like a particle
The first clear demonstration of the particle-like behavior of light was in
The Photoelectric Effect
Albert Einstein won the Nobel Prize in Physics for his study of the Photoelectric Effect
Shining light on a metal can liberate electrons from its surface
The light has to have enough energy (high enough frequency) for this effect to occur
The energy of the ldquophotoelectronsrdquo liberated from the surface depends on the frequency (the energy) of that incident light- NOT its intensity
Increasing the intensity of the light increases the number of photoelectrons emitted but not the energy of each photoelectron
When will Photoelectrons be producedPHet simulation
(Go to PHet website to explore the photoelectric effect simulation)
If no electrons are ejected you musthelliphellipincrease the frequency of the lightIf only a few electrons are ejected and you want
more your musthelliphellipincrease the intensity of the lightIf you want to increase the kinetic energy of the
electrons you musthelliphellipincrease the frequency of the light
hellip and the mathhellipUsing conservation of energyThe energy of the incident photon disappears
Where does it goFirst that energy must be used to liberate the
electron That energy is called the WORK FUNCTION WO Each kind of metal has its unique work function
Any extra energy is given appears in the electron as kinetic energy K
Photon Energy = Work function + Kinetic energy
E = Wo + K
ExamplePhoton energy = Wo + K
A photon with energy 32 eV strikes a metal surface with a work function of 18 eV What is the kinetic energy of the ejected photoelectrons
K = photon energy ndash Wo
K = 32 eV ndash 18 eV
K = 14 eV
ExamplePhoton energy = Wo + K
A photon with energy 28 eV strikes a metal surface If the kinetic energy of the ejected photoelectrons is 05 eV what is the work function of the metal
Wo = photon energy - K
Wo = 28 eV ndash 05 eV
Wo = 23 eV
hf = Wo + frac12 mv2
There is a minimum frequency called the ldquothreshold frequencyrdquo required to liberate an electron At the threshold frequency
Energy of photon = hfthreshold = Wo
That threshold photonrsquos wavelength is called the ldquocutoff wavelengthrdquo and can be found
using
c = f
Now you try some
If the cut-off wavelength for a particular metal is 320 nm what is the metalrsquos work function
First find the threshold frequency using c = f
Threshold frequency fo = 938 x 1014 Hz
Now find the work-function hfo = Wo
Be careful to use Planckrsquos constant with the correct units
h = 663 x 10-34Jmiddots or h = 414 x 10-15 eVmiddots
Wo = 622 x 10-19 J or Wo = 388 eV
What if a 450 nm light hit a surface with a work function of 236 eV What will be the kinetic energy of the photoelectron
First find the frequency of the 450 nm lightf = 667 x 1014 HzNow using conservation of energy
hf = Wo + Kinetic energySo K = hf ndash WoK = 040 eV How fast is the ejected electron movingK = frac12 mv2 m = 91 x 10-31 kg AND you have
to convert K back into Joules first
Each atom has its own unique number of protons neutrons and electrons
Each electron in every element is in an ldquoorbitalrdquo about the nucleus and has a unique energy
That unique energy determines the amazing colors seen in fireworks
bull A Quantum is a discreet unit of a physical quantitybull For example our money is measured in a quantum of
one cent You can have 1 cent 2 cents 8 cents etc but you canrsquot have 124 cents or 1968 cents You must jump from 1 to 2 to 3 to 4 etc
bull Electric charge which ultimately comes from either a proton or an electron is QUANTIZED
bull There is no such thing as a half of an electron or a fifth of a proton so everything that has electrical charge must have some multiple of the charge of an electron or proton- 5 electrons 8 protons etc Thatrsquos why electric charge is QUANTIZED
The electrons in their orbitals about the nucleus have QUANTIZED levels of energy that are determined by which orbital they are in
The orbitals are numbered with ldquonrdquo numbers the ldquoprinciple quantum numberrdquo
n = 1 n = 2 n = 3 etc where the orbital closest to the nucleus is n = 1
The ldquon-numberrdquo for each atomrsquos electrons determine that electronrsquos energy
The larger the ldquonrdquo the larger the energy
What does the energy of an electron in its orbital have to do with the colors of fireworks
When an electron absorbs energy from an external source in any form (heat electricity a collision etc) it jumps to a higher orbital- called an ldquoexcited staterdquo
When the electron falls back down to its original orbital called its ldquorest staterdquo or ldquoground staterdquo it must give up that extra energy The energy is emitted in the form of a photon
Some of those emitted photons are visible light of different colors- some photons are not visible to us like UV or IR or microwaves or X-rays
If an atom is continually absorbing energy all kinds of transitions between higher and lower orbital levels are possible resulting in many different types of emitted photons of many different colors
Metal Color
Strontium Red
Copper Blue
Barium Green
Sodium YellowOrange
Calcium Orange
Gold Iron
What elements are used in fireworks to produce different
colors of light
Atomic Spectra
bull Since the electronsrsquo energy are unique for each element each element produces a unique spectra of colors when supplied energy
bull We may see with our eyes only many overlaping colors of light To see all the distinct colors in the atomrsquos spectra requires a ldquodiffraction gratingrdquo
Spectra for Neon
Each element produces a unique spectra of colored lines when viewed through a diffraction grating
Argon
Helium
Nitrogen
Mercury
Because each element produces a unique emission spectra scientists use ldquospectral analysisrdquo to determine the composition of unknown substances The spectra is like a fingerprint- absolutely unique for each element
Astronomers use ldquospectral analysisrdquo to determine the composition of stars as well
Argon
Using a Spectrometer to determine the identity of a elemental gas
1 The gas will not glow until it is energized Energy can be provided in the form of heat or by applying a high voltage The spectrum analysis power supply shown here provides high voltage
2 If you look at the glowing tube with just a diffraction grating the emission spectrum lines of color are visible
3 If you look at the glowing tube through a ldquospectrometerrdquo which contains a diffraction grating you can actually precisely measure the angles between the lines
4 Those angles allow you to precisely determine the wavelengths (or frequencies) of each of those colors
5 Since each element emits only certain wavelengths the gas can be identified
HydrogenThe emission spectrum of
Hydrogen is the most studied spectrum because it is also the simplest
Hydrogen has only ONE electron
But that ONE electron can be energized to many different orbitals ldquoexcited statesrdquo and will emit photons as it returns to its ldquoground staterdquo
Suppose an electron makes a transition from n = 3 to n = 2 What is the energy of the emitted photon
Energy = E3 ndash E2
E = 1207 eV ndash 1019 eV
E = 188 eV
What is the energy of an emitted photon if an electron makes a transition from n = 4 to n = 1
E = 1273 eVThe higher the energy of the photon the higher its frequency
E = hf
Each color has a different energy The further apart the lines the greater the difference in energy The closer the lines the less the difference in energy
Look at the spectrum for Hydrogen Which two lines have the least difference in energy Which two lines have the greatest difference in energy
Atomic SpectraAbsorption of an external source of
energy results in a transition to a higher energy level
bull A transition back to a lower level must release energy ndash in the form of a photon
bull The frequency of the emitted photon is determined by the difference in the energy levels
Ephoton = E2 ndash E1
Since E = hf the higher the energy the higher the frequency
bull Different frequencies are different colors of light or different types of EM Waves
The Hydrogen
AtomONE
electron
The frequency of the emitted photon is determined by the difference in the energy levelsEphoton = hf = E2 ndash E1
Now you try onehellipbull Get out your calculatorsbull The energized electron in Hydrogen makes a
transition from n = 3 with an energy of -15 eV down to its ground state where its energy is -136 eV
What is the frequency of the emitted photonbull Ephoton = E2 ndash E1 and Ephoton = hfbull Ephoton = -15 eV ndash (-136 eV) = 121 eVbull Ephoton = 121 eV = hf (h = 414 x 10-15 eVs )bull f = 121 eV divide 414 x 10-15 eVs = bull Frequency f = 292 x 1015 Hzbull Is this visible light Use c = f to find the
wavelengthbull wavelength = 102 x 10-7 = 102 nmbull This is NOT visible light- it is UV
Hydrogen EmissionThe energy in eV of the electron in a Hydrogen atom is given by
E =
1Find the energy of the electron at each orbit from n = 1 to n = 7
2 Find the Energy of each photon emitted (Ephoton = E) for these transitions from one orbit to another
4 to 1 5 to 2 6 to 3 7 to 4
3 to 1 4 to 2 5 to 3 6 to 4
2 to 1 3 to 2 4 to 3 5 to 4
3 Find the wavelength for each of those photons and determine what type of electromagnetic wave they are
2n
eV613
Light behaves like a wave AND like a particle
The first clear demonstration of the particle-like behavior of light was in
The Photoelectric Effect
Albert Einstein won the Nobel Prize in Physics for his study of the Photoelectric Effect
Shining light on a metal can liberate electrons from its surface
The light has to have enough energy (high enough frequency) for this effect to occur
The energy of the ldquophotoelectronsrdquo liberated from the surface depends on the frequency (the energy) of that incident light- NOT its intensity
Increasing the intensity of the light increases the number of photoelectrons emitted but not the energy of each photoelectron
When will Photoelectrons be producedPHet simulation
(Go to PHet website to explore the photoelectric effect simulation)
If no electrons are ejected you musthelliphellipincrease the frequency of the lightIf only a few electrons are ejected and you want
more your musthelliphellipincrease the intensity of the lightIf you want to increase the kinetic energy of the
electrons you musthelliphellipincrease the frequency of the light
hellip and the mathhellipUsing conservation of energyThe energy of the incident photon disappears
Where does it goFirst that energy must be used to liberate the
electron That energy is called the WORK FUNCTION WO Each kind of metal has its unique work function
Any extra energy is given appears in the electron as kinetic energy K
Photon Energy = Work function + Kinetic energy
E = Wo + K
ExamplePhoton energy = Wo + K
A photon with energy 32 eV strikes a metal surface with a work function of 18 eV What is the kinetic energy of the ejected photoelectrons
K = photon energy ndash Wo
K = 32 eV ndash 18 eV
K = 14 eV
ExamplePhoton energy = Wo + K
A photon with energy 28 eV strikes a metal surface If the kinetic energy of the ejected photoelectrons is 05 eV what is the work function of the metal
Wo = photon energy - K
Wo = 28 eV ndash 05 eV
Wo = 23 eV
hf = Wo + frac12 mv2
There is a minimum frequency called the ldquothreshold frequencyrdquo required to liberate an electron At the threshold frequency
Energy of photon = hfthreshold = Wo
That threshold photonrsquos wavelength is called the ldquocutoff wavelengthrdquo and can be found
using
c = f
Now you try some
If the cut-off wavelength for a particular metal is 320 nm what is the metalrsquos work function
First find the threshold frequency using c = f
Threshold frequency fo = 938 x 1014 Hz
Now find the work-function hfo = Wo
Be careful to use Planckrsquos constant with the correct units
h = 663 x 10-34Jmiddots or h = 414 x 10-15 eVmiddots
Wo = 622 x 10-19 J or Wo = 388 eV
What if a 450 nm light hit a surface with a work function of 236 eV What will be the kinetic energy of the photoelectron
First find the frequency of the 450 nm lightf = 667 x 1014 HzNow using conservation of energy
hf = Wo + Kinetic energySo K = hf ndash WoK = 040 eV How fast is the ejected electron movingK = frac12 mv2 m = 91 x 10-31 kg AND you have
to convert K back into Joules first
bull A Quantum is a discreet unit of a physical quantitybull For example our money is measured in a quantum of
one cent You can have 1 cent 2 cents 8 cents etc but you canrsquot have 124 cents or 1968 cents You must jump from 1 to 2 to 3 to 4 etc
bull Electric charge which ultimately comes from either a proton or an electron is QUANTIZED
bull There is no such thing as a half of an electron or a fifth of a proton so everything that has electrical charge must have some multiple of the charge of an electron or proton- 5 electrons 8 protons etc Thatrsquos why electric charge is QUANTIZED
The electrons in their orbitals about the nucleus have QUANTIZED levels of energy that are determined by which orbital they are in
The orbitals are numbered with ldquonrdquo numbers the ldquoprinciple quantum numberrdquo
n = 1 n = 2 n = 3 etc where the orbital closest to the nucleus is n = 1
The ldquon-numberrdquo for each atomrsquos electrons determine that electronrsquos energy
The larger the ldquonrdquo the larger the energy
What does the energy of an electron in its orbital have to do with the colors of fireworks
When an electron absorbs energy from an external source in any form (heat electricity a collision etc) it jumps to a higher orbital- called an ldquoexcited staterdquo
When the electron falls back down to its original orbital called its ldquorest staterdquo or ldquoground staterdquo it must give up that extra energy The energy is emitted in the form of a photon
Some of those emitted photons are visible light of different colors- some photons are not visible to us like UV or IR or microwaves or X-rays
If an atom is continually absorbing energy all kinds of transitions between higher and lower orbital levels are possible resulting in many different types of emitted photons of many different colors
Metal Color
Strontium Red
Copper Blue
Barium Green
Sodium YellowOrange
Calcium Orange
Gold Iron
What elements are used in fireworks to produce different
colors of light
Atomic Spectra
bull Since the electronsrsquo energy are unique for each element each element produces a unique spectra of colors when supplied energy
bull We may see with our eyes only many overlaping colors of light To see all the distinct colors in the atomrsquos spectra requires a ldquodiffraction gratingrdquo
Spectra for Neon
Each element produces a unique spectra of colored lines when viewed through a diffraction grating
Argon
Helium
Nitrogen
Mercury
Because each element produces a unique emission spectra scientists use ldquospectral analysisrdquo to determine the composition of unknown substances The spectra is like a fingerprint- absolutely unique for each element
Astronomers use ldquospectral analysisrdquo to determine the composition of stars as well
Argon
Using a Spectrometer to determine the identity of a elemental gas
1 The gas will not glow until it is energized Energy can be provided in the form of heat or by applying a high voltage The spectrum analysis power supply shown here provides high voltage
2 If you look at the glowing tube with just a diffraction grating the emission spectrum lines of color are visible
3 If you look at the glowing tube through a ldquospectrometerrdquo which contains a diffraction grating you can actually precisely measure the angles between the lines
4 Those angles allow you to precisely determine the wavelengths (or frequencies) of each of those colors
5 Since each element emits only certain wavelengths the gas can be identified
HydrogenThe emission spectrum of
Hydrogen is the most studied spectrum because it is also the simplest
Hydrogen has only ONE electron
But that ONE electron can be energized to many different orbitals ldquoexcited statesrdquo and will emit photons as it returns to its ldquoground staterdquo
Suppose an electron makes a transition from n = 3 to n = 2 What is the energy of the emitted photon
Energy = E3 ndash E2
E = 1207 eV ndash 1019 eV
E = 188 eV
What is the energy of an emitted photon if an electron makes a transition from n = 4 to n = 1
E = 1273 eVThe higher the energy of the photon the higher its frequency
E = hf
Each color has a different energy The further apart the lines the greater the difference in energy The closer the lines the less the difference in energy
Look at the spectrum for Hydrogen Which two lines have the least difference in energy Which two lines have the greatest difference in energy
Atomic SpectraAbsorption of an external source of
energy results in a transition to a higher energy level
bull A transition back to a lower level must release energy ndash in the form of a photon
bull The frequency of the emitted photon is determined by the difference in the energy levels
Ephoton = E2 ndash E1
Since E = hf the higher the energy the higher the frequency
bull Different frequencies are different colors of light or different types of EM Waves
The Hydrogen
AtomONE
electron
The frequency of the emitted photon is determined by the difference in the energy levelsEphoton = hf = E2 ndash E1
Now you try onehellipbull Get out your calculatorsbull The energized electron in Hydrogen makes a
transition from n = 3 with an energy of -15 eV down to its ground state where its energy is -136 eV
What is the frequency of the emitted photonbull Ephoton = E2 ndash E1 and Ephoton = hfbull Ephoton = -15 eV ndash (-136 eV) = 121 eVbull Ephoton = 121 eV = hf (h = 414 x 10-15 eVs )bull f = 121 eV divide 414 x 10-15 eVs = bull Frequency f = 292 x 1015 Hzbull Is this visible light Use c = f to find the
wavelengthbull wavelength = 102 x 10-7 = 102 nmbull This is NOT visible light- it is UV
Hydrogen EmissionThe energy in eV of the electron in a Hydrogen atom is given by
E =
1Find the energy of the electron at each orbit from n = 1 to n = 7
2 Find the Energy of each photon emitted (Ephoton = E) for these transitions from one orbit to another
4 to 1 5 to 2 6 to 3 7 to 4
3 to 1 4 to 2 5 to 3 6 to 4
2 to 1 3 to 2 4 to 3 5 to 4
3 Find the wavelength for each of those photons and determine what type of electromagnetic wave they are
2n
eV613
Light behaves like a wave AND like a particle
The first clear demonstration of the particle-like behavior of light was in
The Photoelectric Effect
Albert Einstein won the Nobel Prize in Physics for his study of the Photoelectric Effect
Shining light on a metal can liberate electrons from its surface
The light has to have enough energy (high enough frequency) for this effect to occur
The energy of the ldquophotoelectronsrdquo liberated from the surface depends on the frequency (the energy) of that incident light- NOT its intensity
Increasing the intensity of the light increases the number of photoelectrons emitted but not the energy of each photoelectron
When will Photoelectrons be producedPHet simulation
(Go to PHet website to explore the photoelectric effect simulation)
If no electrons are ejected you musthelliphellipincrease the frequency of the lightIf only a few electrons are ejected and you want
more your musthelliphellipincrease the intensity of the lightIf you want to increase the kinetic energy of the
electrons you musthelliphellipincrease the frequency of the light
hellip and the mathhellipUsing conservation of energyThe energy of the incident photon disappears
Where does it goFirst that energy must be used to liberate the
electron That energy is called the WORK FUNCTION WO Each kind of metal has its unique work function
Any extra energy is given appears in the electron as kinetic energy K
Photon Energy = Work function + Kinetic energy
E = Wo + K
ExamplePhoton energy = Wo + K
A photon with energy 32 eV strikes a metal surface with a work function of 18 eV What is the kinetic energy of the ejected photoelectrons
K = photon energy ndash Wo
K = 32 eV ndash 18 eV
K = 14 eV
ExamplePhoton energy = Wo + K
A photon with energy 28 eV strikes a metal surface If the kinetic energy of the ejected photoelectrons is 05 eV what is the work function of the metal
Wo = photon energy - K
Wo = 28 eV ndash 05 eV
Wo = 23 eV
hf = Wo + frac12 mv2
There is a minimum frequency called the ldquothreshold frequencyrdquo required to liberate an electron At the threshold frequency
Energy of photon = hfthreshold = Wo
That threshold photonrsquos wavelength is called the ldquocutoff wavelengthrdquo and can be found
using
c = f
Now you try some
If the cut-off wavelength for a particular metal is 320 nm what is the metalrsquos work function
First find the threshold frequency using c = f
Threshold frequency fo = 938 x 1014 Hz
Now find the work-function hfo = Wo
Be careful to use Planckrsquos constant with the correct units
h = 663 x 10-34Jmiddots or h = 414 x 10-15 eVmiddots
Wo = 622 x 10-19 J or Wo = 388 eV
What if a 450 nm light hit a surface with a work function of 236 eV What will be the kinetic energy of the photoelectron
First find the frequency of the 450 nm lightf = 667 x 1014 HzNow using conservation of energy
hf = Wo + Kinetic energySo K = hf ndash WoK = 040 eV How fast is the ejected electron movingK = frac12 mv2 m = 91 x 10-31 kg AND you have
to convert K back into Joules first
The electrons in their orbitals about the nucleus have QUANTIZED levels of energy that are determined by which orbital they are in
The orbitals are numbered with ldquonrdquo numbers the ldquoprinciple quantum numberrdquo
n = 1 n = 2 n = 3 etc where the orbital closest to the nucleus is n = 1
The ldquon-numberrdquo for each atomrsquos electrons determine that electronrsquos energy
The larger the ldquonrdquo the larger the energy
What does the energy of an electron in its orbital have to do with the colors of fireworks
When an electron absorbs energy from an external source in any form (heat electricity a collision etc) it jumps to a higher orbital- called an ldquoexcited staterdquo
When the electron falls back down to its original orbital called its ldquorest staterdquo or ldquoground staterdquo it must give up that extra energy The energy is emitted in the form of a photon
Some of those emitted photons are visible light of different colors- some photons are not visible to us like UV or IR or microwaves or X-rays
If an atom is continually absorbing energy all kinds of transitions between higher and lower orbital levels are possible resulting in many different types of emitted photons of many different colors
Metal Color
Strontium Red
Copper Blue
Barium Green
Sodium YellowOrange
Calcium Orange
Gold Iron
What elements are used in fireworks to produce different
colors of light
Atomic Spectra
bull Since the electronsrsquo energy are unique for each element each element produces a unique spectra of colors when supplied energy
bull We may see with our eyes only many overlaping colors of light To see all the distinct colors in the atomrsquos spectra requires a ldquodiffraction gratingrdquo
Spectra for Neon
Each element produces a unique spectra of colored lines when viewed through a diffraction grating
Argon
Helium
Nitrogen
Mercury
Because each element produces a unique emission spectra scientists use ldquospectral analysisrdquo to determine the composition of unknown substances The spectra is like a fingerprint- absolutely unique for each element
Astronomers use ldquospectral analysisrdquo to determine the composition of stars as well
Argon
Using a Spectrometer to determine the identity of a elemental gas
1 The gas will not glow until it is energized Energy can be provided in the form of heat or by applying a high voltage The spectrum analysis power supply shown here provides high voltage
2 If you look at the glowing tube with just a diffraction grating the emission spectrum lines of color are visible
3 If you look at the glowing tube through a ldquospectrometerrdquo which contains a diffraction grating you can actually precisely measure the angles between the lines
4 Those angles allow you to precisely determine the wavelengths (or frequencies) of each of those colors
5 Since each element emits only certain wavelengths the gas can be identified
HydrogenThe emission spectrum of
Hydrogen is the most studied spectrum because it is also the simplest
Hydrogen has only ONE electron
But that ONE electron can be energized to many different orbitals ldquoexcited statesrdquo and will emit photons as it returns to its ldquoground staterdquo
Suppose an electron makes a transition from n = 3 to n = 2 What is the energy of the emitted photon
Energy = E3 ndash E2
E = 1207 eV ndash 1019 eV
E = 188 eV
What is the energy of an emitted photon if an electron makes a transition from n = 4 to n = 1
E = 1273 eVThe higher the energy of the photon the higher its frequency
E = hf
Each color has a different energy The further apart the lines the greater the difference in energy The closer the lines the less the difference in energy
Look at the spectrum for Hydrogen Which two lines have the least difference in energy Which two lines have the greatest difference in energy
Atomic SpectraAbsorption of an external source of
energy results in a transition to a higher energy level
bull A transition back to a lower level must release energy ndash in the form of a photon
bull The frequency of the emitted photon is determined by the difference in the energy levels
Ephoton = E2 ndash E1
Since E = hf the higher the energy the higher the frequency
bull Different frequencies are different colors of light or different types of EM Waves
The Hydrogen
AtomONE
electron
The frequency of the emitted photon is determined by the difference in the energy levelsEphoton = hf = E2 ndash E1
Now you try onehellipbull Get out your calculatorsbull The energized electron in Hydrogen makes a
transition from n = 3 with an energy of -15 eV down to its ground state where its energy is -136 eV
What is the frequency of the emitted photonbull Ephoton = E2 ndash E1 and Ephoton = hfbull Ephoton = -15 eV ndash (-136 eV) = 121 eVbull Ephoton = 121 eV = hf (h = 414 x 10-15 eVs )bull f = 121 eV divide 414 x 10-15 eVs = bull Frequency f = 292 x 1015 Hzbull Is this visible light Use c = f to find the
wavelengthbull wavelength = 102 x 10-7 = 102 nmbull This is NOT visible light- it is UV
Hydrogen EmissionThe energy in eV of the electron in a Hydrogen atom is given by
E =
1Find the energy of the electron at each orbit from n = 1 to n = 7
2 Find the Energy of each photon emitted (Ephoton = E) for these transitions from one orbit to another
4 to 1 5 to 2 6 to 3 7 to 4
3 to 1 4 to 2 5 to 3 6 to 4
2 to 1 3 to 2 4 to 3 5 to 4
3 Find the wavelength for each of those photons and determine what type of electromagnetic wave they are
2n
eV613
Light behaves like a wave AND like a particle
The first clear demonstration of the particle-like behavior of light was in
The Photoelectric Effect
Albert Einstein won the Nobel Prize in Physics for his study of the Photoelectric Effect
Shining light on a metal can liberate electrons from its surface
The light has to have enough energy (high enough frequency) for this effect to occur
The energy of the ldquophotoelectronsrdquo liberated from the surface depends on the frequency (the energy) of that incident light- NOT its intensity
Increasing the intensity of the light increases the number of photoelectrons emitted but not the energy of each photoelectron
When will Photoelectrons be producedPHet simulation
(Go to PHet website to explore the photoelectric effect simulation)
If no electrons are ejected you musthelliphellipincrease the frequency of the lightIf only a few electrons are ejected and you want
more your musthelliphellipincrease the intensity of the lightIf you want to increase the kinetic energy of the
electrons you musthelliphellipincrease the frequency of the light
hellip and the mathhellipUsing conservation of energyThe energy of the incident photon disappears
Where does it goFirst that energy must be used to liberate the
electron That energy is called the WORK FUNCTION WO Each kind of metal has its unique work function
Any extra energy is given appears in the electron as kinetic energy K
Photon Energy = Work function + Kinetic energy
E = Wo + K
ExamplePhoton energy = Wo + K
A photon with energy 32 eV strikes a metal surface with a work function of 18 eV What is the kinetic energy of the ejected photoelectrons
K = photon energy ndash Wo
K = 32 eV ndash 18 eV
K = 14 eV
ExamplePhoton energy = Wo + K
A photon with energy 28 eV strikes a metal surface If the kinetic energy of the ejected photoelectrons is 05 eV what is the work function of the metal
Wo = photon energy - K
Wo = 28 eV ndash 05 eV
Wo = 23 eV
hf = Wo + frac12 mv2
There is a minimum frequency called the ldquothreshold frequencyrdquo required to liberate an electron At the threshold frequency
Energy of photon = hfthreshold = Wo
That threshold photonrsquos wavelength is called the ldquocutoff wavelengthrdquo and can be found
using
c = f
Now you try some
If the cut-off wavelength for a particular metal is 320 nm what is the metalrsquos work function
First find the threshold frequency using c = f
Threshold frequency fo = 938 x 1014 Hz
Now find the work-function hfo = Wo
Be careful to use Planckrsquos constant with the correct units
h = 663 x 10-34Jmiddots or h = 414 x 10-15 eVmiddots
Wo = 622 x 10-19 J or Wo = 388 eV
What if a 450 nm light hit a surface with a work function of 236 eV What will be the kinetic energy of the photoelectron
First find the frequency of the 450 nm lightf = 667 x 1014 HzNow using conservation of energy
hf = Wo + Kinetic energySo K = hf ndash WoK = 040 eV How fast is the ejected electron movingK = frac12 mv2 m = 91 x 10-31 kg AND you have
to convert K back into Joules first
What does the energy of an electron in its orbital have to do with the colors of fireworks
When an electron absorbs energy from an external source in any form (heat electricity a collision etc) it jumps to a higher orbital- called an ldquoexcited staterdquo
When the electron falls back down to its original orbital called its ldquorest staterdquo or ldquoground staterdquo it must give up that extra energy The energy is emitted in the form of a photon
Some of those emitted photons are visible light of different colors- some photons are not visible to us like UV or IR or microwaves or X-rays
If an atom is continually absorbing energy all kinds of transitions between higher and lower orbital levels are possible resulting in many different types of emitted photons of many different colors
Metal Color
Strontium Red
Copper Blue
Barium Green
Sodium YellowOrange
Calcium Orange
Gold Iron
What elements are used in fireworks to produce different
colors of light
Atomic Spectra
bull Since the electronsrsquo energy are unique for each element each element produces a unique spectra of colors when supplied energy
bull We may see with our eyes only many overlaping colors of light To see all the distinct colors in the atomrsquos spectra requires a ldquodiffraction gratingrdquo
Spectra for Neon
Each element produces a unique spectra of colored lines when viewed through a diffraction grating
Argon
Helium
Nitrogen
Mercury
Because each element produces a unique emission spectra scientists use ldquospectral analysisrdquo to determine the composition of unknown substances The spectra is like a fingerprint- absolutely unique for each element
Astronomers use ldquospectral analysisrdquo to determine the composition of stars as well
Argon
Using a Spectrometer to determine the identity of a elemental gas
1 The gas will not glow until it is energized Energy can be provided in the form of heat or by applying a high voltage The spectrum analysis power supply shown here provides high voltage
2 If you look at the glowing tube with just a diffraction grating the emission spectrum lines of color are visible
3 If you look at the glowing tube through a ldquospectrometerrdquo which contains a diffraction grating you can actually precisely measure the angles between the lines
4 Those angles allow you to precisely determine the wavelengths (or frequencies) of each of those colors
5 Since each element emits only certain wavelengths the gas can be identified
HydrogenThe emission spectrum of
Hydrogen is the most studied spectrum because it is also the simplest
Hydrogen has only ONE electron
But that ONE electron can be energized to many different orbitals ldquoexcited statesrdquo and will emit photons as it returns to its ldquoground staterdquo
Suppose an electron makes a transition from n = 3 to n = 2 What is the energy of the emitted photon
Energy = E3 ndash E2
E = 1207 eV ndash 1019 eV
E = 188 eV
What is the energy of an emitted photon if an electron makes a transition from n = 4 to n = 1
E = 1273 eVThe higher the energy of the photon the higher its frequency
E = hf
Each color has a different energy The further apart the lines the greater the difference in energy The closer the lines the less the difference in energy
Look at the spectrum for Hydrogen Which two lines have the least difference in energy Which two lines have the greatest difference in energy
Atomic SpectraAbsorption of an external source of
energy results in a transition to a higher energy level
bull A transition back to a lower level must release energy ndash in the form of a photon
bull The frequency of the emitted photon is determined by the difference in the energy levels
Ephoton = E2 ndash E1
Since E = hf the higher the energy the higher the frequency
bull Different frequencies are different colors of light or different types of EM Waves
The Hydrogen
AtomONE
electron
The frequency of the emitted photon is determined by the difference in the energy levelsEphoton = hf = E2 ndash E1
Now you try onehellipbull Get out your calculatorsbull The energized electron in Hydrogen makes a
transition from n = 3 with an energy of -15 eV down to its ground state where its energy is -136 eV
What is the frequency of the emitted photonbull Ephoton = E2 ndash E1 and Ephoton = hfbull Ephoton = -15 eV ndash (-136 eV) = 121 eVbull Ephoton = 121 eV = hf (h = 414 x 10-15 eVs )bull f = 121 eV divide 414 x 10-15 eVs = bull Frequency f = 292 x 1015 Hzbull Is this visible light Use c = f to find the
wavelengthbull wavelength = 102 x 10-7 = 102 nmbull This is NOT visible light- it is UV
Hydrogen EmissionThe energy in eV of the electron in a Hydrogen atom is given by
E =
1Find the energy of the electron at each orbit from n = 1 to n = 7
2 Find the Energy of each photon emitted (Ephoton = E) for these transitions from one orbit to another
4 to 1 5 to 2 6 to 3 7 to 4
3 to 1 4 to 2 5 to 3 6 to 4
2 to 1 3 to 2 4 to 3 5 to 4
3 Find the wavelength for each of those photons and determine what type of electromagnetic wave they are
2n
eV613
Light behaves like a wave AND like a particle
The first clear demonstration of the particle-like behavior of light was in
The Photoelectric Effect
Albert Einstein won the Nobel Prize in Physics for his study of the Photoelectric Effect
Shining light on a metal can liberate electrons from its surface
The light has to have enough energy (high enough frequency) for this effect to occur
The energy of the ldquophotoelectronsrdquo liberated from the surface depends on the frequency (the energy) of that incident light- NOT its intensity
Increasing the intensity of the light increases the number of photoelectrons emitted but not the energy of each photoelectron
When will Photoelectrons be producedPHet simulation
(Go to PHet website to explore the photoelectric effect simulation)
If no electrons are ejected you musthelliphellipincrease the frequency of the lightIf only a few electrons are ejected and you want
more your musthelliphellipincrease the intensity of the lightIf you want to increase the kinetic energy of the
electrons you musthelliphellipincrease the frequency of the light
hellip and the mathhellipUsing conservation of energyThe energy of the incident photon disappears
Where does it goFirst that energy must be used to liberate the
electron That energy is called the WORK FUNCTION WO Each kind of metal has its unique work function
Any extra energy is given appears in the electron as kinetic energy K
Photon Energy = Work function + Kinetic energy
E = Wo + K
ExamplePhoton energy = Wo + K
A photon with energy 32 eV strikes a metal surface with a work function of 18 eV What is the kinetic energy of the ejected photoelectrons
K = photon energy ndash Wo
K = 32 eV ndash 18 eV
K = 14 eV
ExamplePhoton energy = Wo + K
A photon with energy 28 eV strikes a metal surface If the kinetic energy of the ejected photoelectrons is 05 eV what is the work function of the metal
Wo = photon energy - K
Wo = 28 eV ndash 05 eV
Wo = 23 eV
hf = Wo + frac12 mv2
There is a minimum frequency called the ldquothreshold frequencyrdquo required to liberate an electron At the threshold frequency
Energy of photon = hfthreshold = Wo
That threshold photonrsquos wavelength is called the ldquocutoff wavelengthrdquo and can be found
using
c = f
Now you try some
If the cut-off wavelength for a particular metal is 320 nm what is the metalrsquos work function
First find the threshold frequency using c = f
Threshold frequency fo = 938 x 1014 Hz
Now find the work-function hfo = Wo
Be careful to use Planckrsquos constant with the correct units
h = 663 x 10-34Jmiddots or h = 414 x 10-15 eVmiddots
Wo = 622 x 10-19 J or Wo = 388 eV
What if a 450 nm light hit a surface with a work function of 236 eV What will be the kinetic energy of the photoelectron
First find the frequency of the 450 nm lightf = 667 x 1014 HzNow using conservation of energy
hf = Wo + Kinetic energySo K = hf ndash WoK = 040 eV How fast is the ejected electron movingK = frac12 mv2 m = 91 x 10-31 kg AND you have
to convert K back into Joules first
When an electron absorbs energy from an external source in any form (heat electricity a collision etc) it jumps to a higher orbital- called an ldquoexcited staterdquo
When the electron falls back down to its original orbital called its ldquorest staterdquo or ldquoground staterdquo it must give up that extra energy The energy is emitted in the form of a photon
Some of those emitted photons are visible light of different colors- some photons are not visible to us like UV or IR or microwaves or X-rays
If an atom is continually absorbing energy all kinds of transitions between higher and lower orbital levels are possible resulting in many different types of emitted photons of many different colors
Metal Color
Strontium Red
Copper Blue
Barium Green
Sodium YellowOrange
Calcium Orange
Gold Iron
What elements are used in fireworks to produce different
colors of light
Atomic Spectra
bull Since the electronsrsquo energy are unique for each element each element produces a unique spectra of colors when supplied energy
bull We may see with our eyes only many overlaping colors of light To see all the distinct colors in the atomrsquos spectra requires a ldquodiffraction gratingrdquo
Spectra for Neon
Each element produces a unique spectra of colored lines when viewed through a diffraction grating
Argon
Helium
Nitrogen
Mercury
Because each element produces a unique emission spectra scientists use ldquospectral analysisrdquo to determine the composition of unknown substances The spectra is like a fingerprint- absolutely unique for each element
Astronomers use ldquospectral analysisrdquo to determine the composition of stars as well
Argon
Using a Spectrometer to determine the identity of a elemental gas
1 The gas will not glow until it is energized Energy can be provided in the form of heat or by applying a high voltage The spectrum analysis power supply shown here provides high voltage
2 If you look at the glowing tube with just a diffraction grating the emission spectrum lines of color are visible
3 If you look at the glowing tube through a ldquospectrometerrdquo which contains a diffraction grating you can actually precisely measure the angles between the lines
4 Those angles allow you to precisely determine the wavelengths (or frequencies) of each of those colors
5 Since each element emits only certain wavelengths the gas can be identified
HydrogenThe emission spectrum of
Hydrogen is the most studied spectrum because it is also the simplest
Hydrogen has only ONE electron
But that ONE electron can be energized to many different orbitals ldquoexcited statesrdquo and will emit photons as it returns to its ldquoground staterdquo
Suppose an electron makes a transition from n = 3 to n = 2 What is the energy of the emitted photon
Energy = E3 ndash E2
E = 1207 eV ndash 1019 eV
E = 188 eV
What is the energy of an emitted photon if an electron makes a transition from n = 4 to n = 1
E = 1273 eVThe higher the energy of the photon the higher its frequency
E = hf
Each color has a different energy The further apart the lines the greater the difference in energy The closer the lines the less the difference in energy
Look at the spectrum for Hydrogen Which two lines have the least difference in energy Which two lines have the greatest difference in energy
Atomic SpectraAbsorption of an external source of
energy results in a transition to a higher energy level
bull A transition back to a lower level must release energy ndash in the form of a photon
bull The frequency of the emitted photon is determined by the difference in the energy levels
Ephoton = E2 ndash E1
Since E = hf the higher the energy the higher the frequency
bull Different frequencies are different colors of light or different types of EM Waves
The Hydrogen
AtomONE
electron
The frequency of the emitted photon is determined by the difference in the energy levelsEphoton = hf = E2 ndash E1
Now you try onehellipbull Get out your calculatorsbull The energized electron in Hydrogen makes a
transition from n = 3 with an energy of -15 eV down to its ground state where its energy is -136 eV
What is the frequency of the emitted photonbull Ephoton = E2 ndash E1 and Ephoton = hfbull Ephoton = -15 eV ndash (-136 eV) = 121 eVbull Ephoton = 121 eV = hf (h = 414 x 10-15 eVs )bull f = 121 eV divide 414 x 10-15 eVs = bull Frequency f = 292 x 1015 Hzbull Is this visible light Use c = f to find the
wavelengthbull wavelength = 102 x 10-7 = 102 nmbull This is NOT visible light- it is UV
Hydrogen EmissionThe energy in eV of the electron in a Hydrogen atom is given by
E =
1Find the energy of the electron at each orbit from n = 1 to n = 7
2 Find the Energy of each photon emitted (Ephoton = E) for these transitions from one orbit to another
4 to 1 5 to 2 6 to 3 7 to 4
3 to 1 4 to 2 5 to 3 6 to 4
2 to 1 3 to 2 4 to 3 5 to 4
3 Find the wavelength for each of those photons and determine what type of electromagnetic wave they are
2n
eV613
Light behaves like a wave AND like a particle
The first clear demonstration of the particle-like behavior of light was in
The Photoelectric Effect
Albert Einstein won the Nobel Prize in Physics for his study of the Photoelectric Effect
Shining light on a metal can liberate electrons from its surface
The light has to have enough energy (high enough frequency) for this effect to occur
The energy of the ldquophotoelectronsrdquo liberated from the surface depends on the frequency (the energy) of that incident light- NOT its intensity
Increasing the intensity of the light increases the number of photoelectrons emitted but not the energy of each photoelectron
When will Photoelectrons be producedPHet simulation
(Go to PHet website to explore the photoelectric effect simulation)
If no electrons are ejected you musthelliphellipincrease the frequency of the lightIf only a few electrons are ejected and you want
more your musthelliphellipincrease the intensity of the lightIf you want to increase the kinetic energy of the
electrons you musthelliphellipincrease the frequency of the light
hellip and the mathhellipUsing conservation of energyThe energy of the incident photon disappears
Where does it goFirst that energy must be used to liberate the
electron That energy is called the WORK FUNCTION WO Each kind of metal has its unique work function
Any extra energy is given appears in the electron as kinetic energy K
Photon Energy = Work function + Kinetic energy
E = Wo + K
ExamplePhoton energy = Wo + K
A photon with energy 32 eV strikes a metal surface with a work function of 18 eV What is the kinetic energy of the ejected photoelectrons
K = photon energy ndash Wo
K = 32 eV ndash 18 eV
K = 14 eV
ExamplePhoton energy = Wo + K
A photon with energy 28 eV strikes a metal surface If the kinetic energy of the ejected photoelectrons is 05 eV what is the work function of the metal
Wo = photon energy - K
Wo = 28 eV ndash 05 eV
Wo = 23 eV
hf = Wo + frac12 mv2
There is a minimum frequency called the ldquothreshold frequencyrdquo required to liberate an electron At the threshold frequency
Energy of photon = hfthreshold = Wo
That threshold photonrsquos wavelength is called the ldquocutoff wavelengthrdquo and can be found
using
c = f
Now you try some
If the cut-off wavelength for a particular metal is 320 nm what is the metalrsquos work function
First find the threshold frequency using c = f
Threshold frequency fo = 938 x 1014 Hz
Now find the work-function hfo = Wo
Be careful to use Planckrsquos constant with the correct units
h = 663 x 10-34Jmiddots or h = 414 x 10-15 eVmiddots
Wo = 622 x 10-19 J or Wo = 388 eV
What if a 450 nm light hit a surface with a work function of 236 eV What will be the kinetic energy of the photoelectron
First find the frequency of the 450 nm lightf = 667 x 1014 HzNow using conservation of energy
hf = Wo + Kinetic energySo K = hf ndash WoK = 040 eV How fast is the ejected electron movingK = frac12 mv2 m = 91 x 10-31 kg AND you have
to convert K back into Joules first
When the electron falls back down to its original orbital called its ldquorest staterdquo or ldquoground staterdquo it must give up that extra energy The energy is emitted in the form of a photon
Some of those emitted photons are visible light of different colors- some photons are not visible to us like UV or IR or microwaves or X-rays
If an atom is continually absorbing energy all kinds of transitions between higher and lower orbital levels are possible resulting in many different types of emitted photons of many different colors
Metal Color
Strontium Red
Copper Blue
Barium Green
Sodium YellowOrange
Calcium Orange
Gold Iron
What elements are used in fireworks to produce different
colors of light
Atomic Spectra
bull Since the electronsrsquo energy are unique for each element each element produces a unique spectra of colors when supplied energy
bull We may see with our eyes only many overlaping colors of light To see all the distinct colors in the atomrsquos spectra requires a ldquodiffraction gratingrdquo
Spectra for Neon
Each element produces a unique spectra of colored lines when viewed through a diffraction grating
Argon
Helium
Nitrogen
Mercury
Because each element produces a unique emission spectra scientists use ldquospectral analysisrdquo to determine the composition of unknown substances The spectra is like a fingerprint- absolutely unique for each element
Astronomers use ldquospectral analysisrdquo to determine the composition of stars as well
Argon
Using a Spectrometer to determine the identity of a elemental gas
1 The gas will not glow until it is energized Energy can be provided in the form of heat or by applying a high voltage The spectrum analysis power supply shown here provides high voltage
2 If you look at the glowing tube with just a diffraction grating the emission spectrum lines of color are visible
3 If you look at the glowing tube through a ldquospectrometerrdquo which contains a diffraction grating you can actually precisely measure the angles between the lines
4 Those angles allow you to precisely determine the wavelengths (or frequencies) of each of those colors
5 Since each element emits only certain wavelengths the gas can be identified
HydrogenThe emission spectrum of
Hydrogen is the most studied spectrum because it is also the simplest
Hydrogen has only ONE electron
But that ONE electron can be energized to many different orbitals ldquoexcited statesrdquo and will emit photons as it returns to its ldquoground staterdquo
Suppose an electron makes a transition from n = 3 to n = 2 What is the energy of the emitted photon
Energy = E3 ndash E2
E = 1207 eV ndash 1019 eV
E = 188 eV
What is the energy of an emitted photon if an electron makes a transition from n = 4 to n = 1
E = 1273 eVThe higher the energy of the photon the higher its frequency
E = hf
Each color has a different energy The further apart the lines the greater the difference in energy The closer the lines the less the difference in energy
Look at the spectrum for Hydrogen Which two lines have the least difference in energy Which two lines have the greatest difference in energy
Atomic SpectraAbsorption of an external source of
energy results in a transition to a higher energy level
bull A transition back to a lower level must release energy ndash in the form of a photon
bull The frequency of the emitted photon is determined by the difference in the energy levels
Ephoton = E2 ndash E1
Since E = hf the higher the energy the higher the frequency
bull Different frequencies are different colors of light or different types of EM Waves
The Hydrogen
AtomONE
electron
The frequency of the emitted photon is determined by the difference in the energy levelsEphoton = hf = E2 ndash E1
Now you try onehellipbull Get out your calculatorsbull The energized electron in Hydrogen makes a
transition from n = 3 with an energy of -15 eV down to its ground state where its energy is -136 eV
What is the frequency of the emitted photonbull Ephoton = E2 ndash E1 and Ephoton = hfbull Ephoton = -15 eV ndash (-136 eV) = 121 eVbull Ephoton = 121 eV = hf (h = 414 x 10-15 eVs )bull f = 121 eV divide 414 x 10-15 eVs = bull Frequency f = 292 x 1015 Hzbull Is this visible light Use c = f to find the
wavelengthbull wavelength = 102 x 10-7 = 102 nmbull This is NOT visible light- it is UV
Hydrogen EmissionThe energy in eV of the electron in a Hydrogen atom is given by
E =
1Find the energy of the electron at each orbit from n = 1 to n = 7
2 Find the Energy of each photon emitted (Ephoton = E) for these transitions from one orbit to another
4 to 1 5 to 2 6 to 3 7 to 4
3 to 1 4 to 2 5 to 3 6 to 4
2 to 1 3 to 2 4 to 3 5 to 4
3 Find the wavelength for each of those photons and determine what type of electromagnetic wave they are
2n
eV613
Light behaves like a wave AND like a particle
The first clear demonstration of the particle-like behavior of light was in
The Photoelectric Effect
Albert Einstein won the Nobel Prize in Physics for his study of the Photoelectric Effect
Shining light on a metal can liberate electrons from its surface
The light has to have enough energy (high enough frequency) for this effect to occur
The energy of the ldquophotoelectronsrdquo liberated from the surface depends on the frequency (the energy) of that incident light- NOT its intensity
Increasing the intensity of the light increases the number of photoelectrons emitted but not the energy of each photoelectron
When will Photoelectrons be producedPHet simulation
(Go to PHet website to explore the photoelectric effect simulation)
If no electrons are ejected you musthelliphellipincrease the frequency of the lightIf only a few electrons are ejected and you want
more your musthelliphellipincrease the intensity of the lightIf you want to increase the kinetic energy of the
electrons you musthelliphellipincrease the frequency of the light
hellip and the mathhellipUsing conservation of energyThe energy of the incident photon disappears
Where does it goFirst that energy must be used to liberate the
electron That energy is called the WORK FUNCTION WO Each kind of metal has its unique work function
Any extra energy is given appears in the electron as kinetic energy K
Photon Energy = Work function + Kinetic energy
E = Wo + K
ExamplePhoton energy = Wo + K
A photon with energy 32 eV strikes a metal surface with a work function of 18 eV What is the kinetic energy of the ejected photoelectrons
K = photon energy ndash Wo
K = 32 eV ndash 18 eV
K = 14 eV
ExamplePhoton energy = Wo + K
A photon with energy 28 eV strikes a metal surface If the kinetic energy of the ejected photoelectrons is 05 eV what is the work function of the metal
Wo = photon energy - K
Wo = 28 eV ndash 05 eV
Wo = 23 eV
hf = Wo + frac12 mv2
There is a minimum frequency called the ldquothreshold frequencyrdquo required to liberate an electron At the threshold frequency
Energy of photon = hfthreshold = Wo
That threshold photonrsquos wavelength is called the ldquocutoff wavelengthrdquo and can be found
using
c = f
Now you try some
If the cut-off wavelength for a particular metal is 320 nm what is the metalrsquos work function
First find the threshold frequency using c = f
Threshold frequency fo = 938 x 1014 Hz
Now find the work-function hfo = Wo
Be careful to use Planckrsquos constant with the correct units
h = 663 x 10-34Jmiddots or h = 414 x 10-15 eVmiddots
Wo = 622 x 10-19 J or Wo = 388 eV
What if a 450 nm light hit a surface with a work function of 236 eV What will be the kinetic energy of the photoelectron
First find the frequency of the 450 nm lightf = 667 x 1014 HzNow using conservation of energy
hf = Wo + Kinetic energySo K = hf ndash WoK = 040 eV How fast is the ejected electron movingK = frac12 mv2 m = 91 x 10-31 kg AND you have
to convert K back into Joules first
If an atom is continually absorbing energy all kinds of transitions between higher and lower orbital levels are possible resulting in many different types of emitted photons of many different colors
Metal Color
Strontium Red
Copper Blue
Barium Green
Sodium YellowOrange
Calcium Orange
Gold Iron
What elements are used in fireworks to produce different
colors of light
Atomic Spectra
bull Since the electronsrsquo energy are unique for each element each element produces a unique spectra of colors when supplied energy
bull We may see with our eyes only many overlaping colors of light To see all the distinct colors in the atomrsquos spectra requires a ldquodiffraction gratingrdquo
Spectra for Neon
Each element produces a unique spectra of colored lines when viewed through a diffraction grating
Argon
Helium
Nitrogen
Mercury
Because each element produces a unique emission spectra scientists use ldquospectral analysisrdquo to determine the composition of unknown substances The spectra is like a fingerprint- absolutely unique for each element
Astronomers use ldquospectral analysisrdquo to determine the composition of stars as well
Argon
Using a Spectrometer to determine the identity of a elemental gas
1 The gas will not glow until it is energized Energy can be provided in the form of heat or by applying a high voltage The spectrum analysis power supply shown here provides high voltage
2 If you look at the glowing tube with just a diffraction grating the emission spectrum lines of color are visible
3 If you look at the glowing tube through a ldquospectrometerrdquo which contains a diffraction grating you can actually precisely measure the angles between the lines
4 Those angles allow you to precisely determine the wavelengths (or frequencies) of each of those colors
5 Since each element emits only certain wavelengths the gas can be identified
HydrogenThe emission spectrum of
Hydrogen is the most studied spectrum because it is also the simplest
Hydrogen has only ONE electron
But that ONE electron can be energized to many different orbitals ldquoexcited statesrdquo and will emit photons as it returns to its ldquoground staterdquo
Suppose an electron makes a transition from n = 3 to n = 2 What is the energy of the emitted photon
Energy = E3 ndash E2
E = 1207 eV ndash 1019 eV
E = 188 eV
What is the energy of an emitted photon if an electron makes a transition from n = 4 to n = 1
E = 1273 eVThe higher the energy of the photon the higher its frequency
E = hf
Each color has a different energy The further apart the lines the greater the difference in energy The closer the lines the less the difference in energy
Look at the spectrum for Hydrogen Which two lines have the least difference in energy Which two lines have the greatest difference in energy
Atomic SpectraAbsorption of an external source of
energy results in a transition to a higher energy level
bull A transition back to a lower level must release energy ndash in the form of a photon
bull The frequency of the emitted photon is determined by the difference in the energy levels
Ephoton = E2 ndash E1
Since E = hf the higher the energy the higher the frequency
bull Different frequencies are different colors of light or different types of EM Waves
The Hydrogen
AtomONE
electron
The frequency of the emitted photon is determined by the difference in the energy levelsEphoton = hf = E2 ndash E1
Now you try onehellipbull Get out your calculatorsbull The energized electron in Hydrogen makes a
transition from n = 3 with an energy of -15 eV down to its ground state where its energy is -136 eV
What is the frequency of the emitted photonbull Ephoton = E2 ndash E1 and Ephoton = hfbull Ephoton = -15 eV ndash (-136 eV) = 121 eVbull Ephoton = 121 eV = hf (h = 414 x 10-15 eVs )bull f = 121 eV divide 414 x 10-15 eVs = bull Frequency f = 292 x 1015 Hzbull Is this visible light Use c = f to find the
wavelengthbull wavelength = 102 x 10-7 = 102 nmbull This is NOT visible light- it is UV
Hydrogen EmissionThe energy in eV of the electron in a Hydrogen atom is given by
E =
1Find the energy of the electron at each orbit from n = 1 to n = 7
2 Find the Energy of each photon emitted (Ephoton = E) for these transitions from one orbit to another
4 to 1 5 to 2 6 to 3 7 to 4
3 to 1 4 to 2 5 to 3 6 to 4
2 to 1 3 to 2 4 to 3 5 to 4
3 Find the wavelength for each of those photons and determine what type of electromagnetic wave they are
2n
eV613
Light behaves like a wave AND like a particle
The first clear demonstration of the particle-like behavior of light was in
The Photoelectric Effect
Albert Einstein won the Nobel Prize in Physics for his study of the Photoelectric Effect
Shining light on a metal can liberate electrons from its surface
The light has to have enough energy (high enough frequency) for this effect to occur
The energy of the ldquophotoelectronsrdquo liberated from the surface depends on the frequency (the energy) of that incident light- NOT its intensity
Increasing the intensity of the light increases the number of photoelectrons emitted but not the energy of each photoelectron
When will Photoelectrons be producedPHet simulation
(Go to PHet website to explore the photoelectric effect simulation)
If no electrons are ejected you musthelliphellipincrease the frequency of the lightIf only a few electrons are ejected and you want
more your musthelliphellipincrease the intensity of the lightIf you want to increase the kinetic energy of the
electrons you musthelliphellipincrease the frequency of the light
hellip and the mathhellipUsing conservation of energyThe energy of the incident photon disappears
Where does it goFirst that energy must be used to liberate the
electron That energy is called the WORK FUNCTION WO Each kind of metal has its unique work function
Any extra energy is given appears in the electron as kinetic energy K
Photon Energy = Work function + Kinetic energy
E = Wo + K
ExamplePhoton energy = Wo + K
A photon with energy 32 eV strikes a metal surface with a work function of 18 eV What is the kinetic energy of the ejected photoelectrons
K = photon energy ndash Wo
K = 32 eV ndash 18 eV
K = 14 eV
ExamplePhoton energy = Wo + K
A photon with energy 28 eV strikes a metal surface If the kinetic energy of the ejected photoelectrons is 05 eV what is the work function of the metal
Wo = photon energy - K
Wo = 28 eV ndash 05 eV
Wo = 23 eV
hf = Wo + frac12 mv2
There is a minimum frequency called the ldquothreshold frequencyrdquo required to liberate an electron At the threshold frequency
Energy of photon = hfthreshold = Wo
That threshold photonrsquos wavelength is called the ldquocutoff wavelengthrdquo and can be found
using
c = f
Now you try some
If the cut-off wavelength for a particular metal is 320 nm what is the metalrsquos work function
First find the threshold frequency using c = f
Threshold frequency fo = 938 x 1014 Hz
Now find the work-function hfo = Wo
Be careful to use Planckrsquos constant with the correct units
h = 663 x 10-34Jmiddots or h = 414 x 10-15 eVmiddots
Wo = 622 x 10-19 J or Wo = 388 eV
What if a 450 nm light hit a surface with a work function of 236 eV What will be the kinetic energy of the photoelectron
First find the frequency of the 450 nm lightf = 667 x 1014 HzNow using conservation of energy
hf = Wo + Kinetic energySo K = hf ndash WoK = 040 eV How fast is the ejected electron movingK = frac12 mv2 m = 91 x 10-31 kg AND you have
to convert K back into Joules first
Metal Color
Strontium Red
Copper Blue
Barium Green
Sodium YellowOrange
Calcium Orange
Gold Iron
What elements are used in fireworks to produce different
colors of light
Atomic Spectra
bull Since the electronsrsquo energy are unique for each element each element produces a unique spectra of colors when supplied energy
bull We may see with our eyes only many overlaping colors of light To see all the distinct colors in the atomrsquos spectra requires a ldquodiffraction gratingrdquo
Spectra for Neon
Each element produces a unique spectra of colored lines when viewed through a diffraction grating
Argon
Helium
Nitrogen
Mercury
Because each element produces a unique emission spectra scientists use ldquospectral analysisrdquo to determine the composition of unknown substances The spectra is like a fingerprint- absolutely unique for each element
Astronomers use ldquospectral analysisrdquo to determine the composition of stars as well
Argon
Using a Spectrometer to determine the identity of a elemental gas
1 The gas will not glow until it is energized Energy can be provided in the form of heat or by applying a high voltage The spectrum analysis power supply shown here provides high voltage
2 If you look at the glowing tube with just a diffraction grating the emission spectrum lines of color are visible
3 If you look at the glowing tube through a ldquospectrometerrdquo which contains a diffraction grating you can actually precisely measure the angles between the lines
4 Those angles allow you to precisely determine the wavelengths (or frequencies) of each of those colors
5 Since each element emits only certain wavelengths the gas can be identified
HydrogenThe emission spectrum of
Hydrogen is the most studied spectrum because it is also the simplest
Hydrogen has only ONE electron
But that ONE electron can be energized to many different orbitals ldquoexcited statesrdquo and will emit photons as it returns to its ldquoground staterdquo
Suppose an electron makes a transition from n = 3 to n = 2 What is the energy of the emitted photon
Energy = E3 ndash E2
E = 1207 eV ndash 1019 eV
E = 188 eV
What is the energy of an emitted photon if an electron makes a transition from n = 4 to n = 1
E = 1273 eVThe higher the energy of the photon the higher its frequency
E = hf
Each color has a different energy The further apart the lines the greater the difference in energy The closer the lines the less the difference in energy
Look at the spectrum for Hydrogen Which two lines have the least difference in energy Which two lines have the greatest difference in energy
Atomic SpectraAbsorption of an external source of
energy results in a transition to a higher energy level
bull A transition back to a lower level must release energy ndash in the form of a photon
bull The frequency of the emitted photon is determined by the difference in the energy levels
Ephoton = E2 ndash E1
Since E = hf the higher the energy the higher the frequency
bull Different frequencies are different colors of light or different types of EM Waves
The Hydrogen
AtomONE
electron
The frequency of the emitted photon is determined by the difference in the energy levelsEphoton = hf = E2 ndash E1
Now you try onehellipbull Get out your calculatorsbull The energized electron in Hydrogen makes a
transition from n = 3 with an energy of -15 eV down to its ground state where its energy is -136 eV
What is the frequency of the emitted photonbull Ephoton = E2 ndash E1 and Ephoton = hfbull Ephoton = -15 eV ndash (-136 eV) = 121 eVbull Ephoton = 121 eV = hf (h = 414 x 10-15 eVs )bull f = 121 eV divide 414 x 10-15 eVs = bull Frequency f = 292 x 1015 Hzbull Is this visible light Use c = f to find the
wavelengthbull wavelength = 102 x 10-7 = 102 nmbull This is NOT visible light- it is UV
Hydrogen EmissionThe energy in eV of the electron in a Hydrogen atom is given by
E =
1Find the energy of the electron at each orbit from n = 1 to n = 7
2 Find the Energy of each photon emitted (Ephoton = E) for these transitions from one orbit to another
4 to 1 5 to 2 6 to 3 7 to 4
3 to 1 4 to 2 5 to 3 6 to 4
2 to 1 3 to 2 4 to 3 5 to 4
3 Find the wavelength for each of those photons and determine what type of electromagnetic wave they are
2n
eV613
Light behaves like a wave AND like a particle
The first clear demonstration of the particle-like behavior of light was in
The Photoelectric Effect
Albert Einstein won the Nobel Prize in Physics for his study of the Photoelectric Effect
Shining light on a metal can liberate electrons from its surface
The light has to have enough energy (high enough frequency) for this effect to occur
The energy of the ldquophotoelectronsrdquo liberated from the surface depends on the frequency (the energy) of that incident light- NOT its intensity
Increasing the intensity of the light increases the number of photoelectrons emitted but not the energy of each photoelectron
When will Photoelectrons be producedPHet simulation
(Go to PHet website to explore the photoelectric effect simulation)
If no electrons are ejected you musthelliphellipincrease the frequency of the lightIf only a few electrons are ejected and you want
more your musthelliphellipincrease the intensity of the lightIf you want to increase the kinetic energy of the
electrons you musthelliphellipincrease the frequency of the light
hellip and the mathhellipUsing conservation of energyThe energy of the incident photon disappears
Where does it goFirst that energy must be used to liberate the
electron That energy is called the WORK FUNCTION WO Each kind of metal has its unique work function
Any extra energy is given appears in the electron as kinetic energy K
Photon Energy = Work function + Kinetic energy
E = Wo + K
ExamplePhoton energy = Wo + K
A photon with energy 32 eV strikes a metal surface with a work function of 18 eV What is the kinetic energy of the ejected photoelectrons
K = photon energy ndash Wo
K = 32 eV ndash 18 eV
K = 14 eV
ExamplePhoton energy = Wo + K
A photon with energy 28 eV strikes a metal surface If the kinetic energy of the ejected photoelectrons is 05 eV what is the work function of the metal
Wo = photon energy - K
Wo = 28 eV ndash 05 eV
Wo = 23 eV
hf = Wo + frac12 mv2
There is a minimum frequency called the ldquothreshold frequencyrdquo required to liberate an electron At the threshold frequency
Energy of photon = hfthreshold = Wo
That threshold photonrsquos wavelength is called the ldquocutoff wavelengthrdquo and can be found
using
c = f
Now you try some
If the cut-off wavelength for a particular metal is 320 nm what is the metalrsquos work function
First find the threshold frequency using c = f
Threshold frequency fo = 938 x 1014 Hz
Now find the work-function hfo = Wo
Be careful to use Planckrsquos constant with the correct units
h = 663 x 10-34Jmiddots or h = 414 x 10-15 eVmiddots
Wo = 622 x 10-19 J or Wo = 388 eV
What if a 450 nm light hit a surface with a work function of 236 eV What will be the kinetic energy of the photoelectron
First find the frequency of the 450 nm lightf = 667 x 1014 HzNow using conservation of energy
hf = Wo + Kinetic energySo K = hf ndash WoK = 040 eV How fast is the ejected electron movingK = frac12 mv2 m = 91 x 10-31 kg AND you have
to convert K back into Joules first
Atomic Spectra
bull Since the electronsrsquo energy are unique for each element each element produces a unique spectra of colors when supplied energy
bull We may see with our eyes only many overlaping colors of light To see all the distinct colors in the atomrsquos spectra requires a ldquodiffraction gratingrdquo
Spectra for Neon
Each element produces a unique spectra of colored lines when viewed through a diffraction grating
Argon
Helium
Nitrogen
Mercury
Because each element produces a unique emission spectra scientists use ldquospectral analysisrdquo to determine the composition of unknown substances The spectra is like a fingerprint- absolutely unique for each element
Astronomers use ldquospectral analysisrdquo to determine the composition of stars as well
Argon
Using a Spectrometer to determine the identity of a elemental gas
1 The gas will not glow until it is energized Energy can be provided in the form of heat or by applying a high voltage The spectrum analysis power supply shown here provides high voltage
2 If you look at the glowing tube with just a diffraction grating the emission spectrum lines of color are visible
3 If you look at the glowing tube through a ldquospectrometerrdquo which contains a diffraction grating you can actually precisely measure the angles between the lines
4 Those angles allow you to precisely determine the wavelengths (or frequencies) of each of those colors
5 Since each element emits only certain wavelengths the gas can be identified
HydrogenThe emission spectrum of
Hydrogen is the most studied spectrum because it is also the simplest
Hydrogen has only ONE electron
But that ONE electron can be energized to many different orbitals ldquoexcited statesrdquo and will emit photons as it returns to its ldquoground staterdquo
Suppose an electron makes a transition from n = 3 to n = 2 What is the energy of the emitted photon
Energy = E3 ndash E2
E = 1207 eV ndash 1019 eV
E = 188 eV
What is the energy of an emitted photon if an electron makes a transition from n = 4 to n = 1
E = 1273 eVThe higher the energy of the photon the higher its frequency
E = hf
Each color has a different energy The further apart the lines the greater the difference in energy The closer the lines the less the difference in energy
Look at the spectrum for Hydrogen Which two lines have the least difference in energy Which two lines have the greatest difference in energy
Atomic SpectraAbsorption of an external source of
energy results in a transition to a higher energy level
bull A transition back to a lower level must release energy ndash in the form of a photon
bull The frequency of the emitted photon is determined by the difference in the energy levels
Ephoton = E2 ndash E1
Since E = hf the higher the energy the higher the frequency
bull Different frequencies are different colors of light or different types of EM Waves
The Hydrogen
AtomONE
electron
The frequency of the emitted photon is determined by the difference in the energy levelsEphoton = hf = E2 ndash E1
Now you try onehellipbull Get out your calculatorsbull The energized electron in Hydrogen makes a
transition from n = 3 with an energy of -15 eV down to its ground state where its energy is -136 eV
What is the frequency of the emitted photonbull Ephoton = E2 ndash E1 and Ephoton = hfbull Ephoton = -15 eV ndash (-136 eV) = 121 eVbull Ephoton = 121 eV = hf (h = 414 x 10-15 eVs )bull f = 121 eV divide 414 x 10-15 eVs = bull Frequency f = 292 x 1015 Hzbull Is this visible light Use c = f to find the
wavelengthbull wavelength = 102 x 10-7 = 102 nmbull This is NOT visible light- it is UV
Hydrogen EmissionThe energy in eV of the electron in a Hydrogen atom is given by
E =
1Find the energy of the electron at each orbit from n = 1 to n = 7
2 Find the Energy of each photon emitted (Ephoton = E) for these transitions from one orbit to another
4 to 1 5 to 2 6 to 3 7 to 4
3 to 1 4 to 2 5 to 3 6 to 4
2 to 1 3 to 2 4 to 3 5 to 4
3 Find the wavelength for each of those photons and determine what type of electromagnetic wave they are
2n
eV613
Light behaves like a wave AND like a particle
The first clear demonstration of the particle-like behavior of light was in
The Photoelectric Effect
Albert Einstein won the Nobel Prize in Physics for his study of the Photoelectric Effect
Shining light on a metal can liberate electrons from its surface
The light has to have enough energy (high enough frequency) for this effect to occur
The energy of the ldquophotoelectronsrdquo liberated from the surface depends on the frequency (the energy) of that incident light- NOT its intensity
Increasing the intensity of the light increases the number of photoelectrons emitted but not the energy of each photoelectron
When will Photoelectrons be producedPHet simulation
(Go to PHet website to explore the photoelectric effect simulation)
If no electrons are ejected you musthelliphellipincrease the frequency of the lightIf only a few electrons are ejected and you want
more your musthelliphellipincrease the intensity of the lightIf you want to increase the kinetic energy of the
electrons you musthelliphellipincrease the frequency of the light
hellip and the mathhellipUsing conservation of energyThe energy of the incident photon disappears
Where does it goFirst that energy must be used to liberate the
electron That energy is called the WORK FUNCTION WO Each kind of metal has its unique work function
Any extra energy is given appears in the electron as kinetic energy K
Photon Energy = Work function + Kinetic energy
E = Wo + K
ExamplePhoton energy = Wo + K
A photon with energy 32 eV strikes a metal surface with a work function of 18 eV What is the kinetic energy of the ejected photoelectrons
K = photon energy ndash Wo
K = 32 eV ndash 18 eV
K = 14 eV
ExamplePhoton energy = Wo + K
A photon with energy 28 eV strikes a metal surface If the kinetic energy of the ejected photoelectrons is 05 eV what is the work function of the metal
Wo = photon energy - K
Wo = 28 eV ndash 05 eV
Wo = 23 eV
hf = Wo + frac12 mv2
There is a minimum frequency called the ldquothreshold frequencyrdquo required to liberate an electron At the threshold frequency
Energy of photon = hfthreshold = Wo
That threshold photonrsquos wavelength is called the ldquocutoff wavelengthrdquo and can be found
using
c = f
Now you try some
If the cut-off wavelength for a particular metal is 320 nm what is the metalrsquos work function
First find the threshold frequency using c = f
Threshold frequency fo = 938 x 1014 Hz
Now find the work-function hfo = Wo
Be careful to use Planckrsquos constant with the correct units
h = 663 x 10-34Jmiddots or h = 414 x 10-15 eVmiddots
Wo = 622 x 10-19 J or Wo = 388 eV
What if a 450 nm light hit a surface with a work function of 236 eV What will be the kinetic energy of the photoelectron
First find the frequency of the 450 nm lightf = 667 x 1014 HzNow using conservation of energy
hf = Wo + Kinetic energySo K = hf ndash WoK = 040 eV How fast is the ejected electron movingK = frac12 mv2 m = 91 x 10-31 kg AND you have
to convert K back into Joules first
Each element produces a unique spectra of colored lines when viewed through a diffraction grating
Argon
Helium
Nitrogen
Mercury
Because each element produces a unique emission spectra scientists use ldquospectral analysisrdquo to determine the composition of unknown substances The spectra is like a fingerprint- absolutely unique for each element
Astronomers use ldquospectral analysisrdquo to determine the composition of stars as well
Argon
Using a Spectrometer to determine the identity of a elemental gas
1 The gas will not glow until it is energized Energy can be provided in the form of heat or by applying a high voltage The spectrum analysis power supply shown here provides high voltage
2 If you look at the glowing tube with just a diffraction grating the emission spectrum lines of color are visible
3 If you look at the glowing tube through a ldquospectrometerrdquo which contains a diffraction grating you can actually precisely measure the angles between the lines
4 Those angles allow you to precisely determine the wavelengths (or frequencies) of each of those colors
5 Since each element emits only certain wavelengths the gas can be identified
HydrogenThe emission spectrum of
Hydrogen is the most studied spectrum because it is also the simplest
Hydrogen has only ONE electron
But that ONE electron can be energized to many different orbitals ldquoexcited statesrdquo and will emit photons as it returns to its ldquoground staterdquo
Suppose an electron makes a transition from n = 3 to n = 2 What is the energy of the emitted photon
Energy = E3 ndash E2
E = 1207 eV ndash 1019 eV
E = 188 eV
What is the energy of an emitted photon if an electron makes a transition from n = 4 to n = 1
E = 1273 eVThe higher the energy of the photon the higher its frequency
E = hf
Each color has a different energy The further apart the lines the greater the difference in energy The closer the lines the less the difference in energy
Look at the spectrum for Hydrogen Which two lines have the least difference in energy Which two lines have the greatest difference in energy
Atomic SpectraAbsorption of an external source of
energy results in a transition to a higher energy level
bull A transition back to a lower level must release energy ndash in the form of a photon
bull The frequency of the emitted photon is determined by the difference in the energy levels
Ephoton = E2 ndash E1
Since E = hf the higher the energy the higher the frequency
bull Different frequencies are different colors of light or different types of EM Waves
The Hydrogen
AtomONE
electron
The frequency of the emitted photon is determined by the difference in the energy levelsEphoton = hf = E2 ndash E1
Now you try onehellipbull Get out your calculatorsbull The energized electron in Hydrogen makes a
transition from n = 3 with an energy of -15 eV down to its ground state where its energy is -136 eV
What is the frequency of the emitted photonbull Ephoton = E2 ndash E1 and Ephoton = hfbull Ephoton = -15 eV ndash (-136 eV) = 121 eVbull Ephoton = 121 eV = hf (h = 414 x 10-15 eVs )bull f = 121 eV divide 414 x 10-15 eVs = bull Frequency f = 292 x 1015 Hzbull Is this visible light Use c = f to find the
wavelengthbull wavelength = 102 x 10-7 = 102 nmbull This is NOT visible light- it is UV
Hydrogen EmissionThe energy in eV of the electron in a Hydrogen atom is given by
E =
1Find the energy of the electron at each orbit from n = 1 to n = 7
2 Find the Energy of each photon emitted (Ephoton = E) for these transitions from one orbit to another
4 to 1 5 to 2 6 to 3 7 to 4
3 to 1 4 to 2 5 to 3 6 to 4
2 to 1 3 to 2 4 to 3 5 to 4
3 Find the wavelength for each of those photons and determine what type of electromagnetic wave they are
2n
eV613
Light behaves like a wave AND like a particle
The first clear demonstration of the particle-like behavior of light was in
The Photoelectric Effect
Albert Einstein won the Nobel Prize in Physics for his study of the Photoelectric Effect
Shining light on a metal can liberate electrons from its surface
The light has to have enough energy (high enough frequency) for this effect to occur
The energy of the ldquophotoelectronsrdquo liberated from the surface depends on the frequency (the energy) of that incident light- NOT its intensity
Increasing the intensity of the light increases the number of photoelectrons emitted but not the energy of each photoelectron
When will Photoelectrons be producedPHet simulation
(Go to PHet website to explore the photoelectric effect simulation)
If no electrons are ejected you musthelliphellipincrease the frequency of the lightIf only a few electrons are ejected and you want
more your musthelliphellipincrease the intensity of the lightIf you want to increase the kinetic energy of the
electrons you musthelliphellipincrease the frequency of the light
hellip and the mathhellipUsing conservation of energyThe energy of the incident photon disappears
Where does it goFirst that energy must be used to liberate the
electron That energy is called the WORK FUNCTION WO Each kind of metal has its unique work function
Any extra energy is given appears in the electron as kinetic energy K
Photon Energy = Work function + Kinetic energy
E = Wo + K
ExamplePhoton energy = Wo + K
A photon with energy 32 eV strikes a metal surface with a work function of 18 eV What is the kinetic energy of the ejected photoelectrons
K = photon energy ndash Wo
K = 32 eV ndash 18 eV
K = 14 eV
ExamplePhoton energy = Wo + K
A photon with energy 28 eV strikes a metal surface If the kinetic energy of the ejected photoelectrons is 05 eV what is the work function of the metal
Wo = photon energy - K
Wo = 28 eV ndash 05 eV
Wo = 23 eV
hf = Wo + frac12 mv2
There is a minimum frequency called the ldquothreshold frequencyrdquo required to liberate an electron At the threshold frequency
Energy of photon = hfthreshold = Wo
That threshold photonrsquos wavelength is called the ldquocutoff wavelengthrdquo and can be found
using
c = f
Now you try some
If the cut-off wavelength for a particular metal is 320 nm what is the metalrsquos work function
First find the threshold frequency using c = f
Threshold frequency fo = 938 x 1014 Hz
Now find the work-function hfo = Wo
Be careful to use Planckrsquos constant with the correct units
h = 663 x 10-34Jmiddots or h = 414 x 10-15 eVmiddots
Wo = 622 x 10-19 J or Wo = 388 eV
What if a 450 nm light hit a surface with a work function of 236 eV What will be the kinetic energy of the photoelectron
First find the frequency of the 450 nm lightf = 667 x 1014 HzNow using conservation of energy
hf = Wo + Kinetic energySo K = hf ndash WoK = 040 eV How fast is the ejected electron movingK = frac12 mv2 m = 91 x 10-31 kg AND you have
to convert K back into Joules first
Because each element produces a unique emission spectra scientists use ldquospectral analysisrdquo to determine the composition of unknown substances The spectra is like a fingerprint- absolutely unique for each element
Astronomers use ldquospectral analysisrdquo to determine the composition of stars as well
Argon
Using a Spectrometer to determine the identity of a elemental gas
1 The gas will not glow until it is energized Energy can be provided in the form of heat or by applying a high voltage The spectrum analysis power supply shown here provides high voltage
2 If you look at the glowing tube with just a diffraction grating the emission spectrum lines of color are visible
3 If you look at the glowing tube through a ldquospectrometerrdquo which contains a diffraction grating you can actually precisely measure the angles between the lines
4 Those angles allow you to precisely determine the wavelengths (or frequencies) of each of those colors
5 Since each element emits only certain wavelengths the gas can be identified
HydrogenThe emission spectrum of
Hydrogen is the most studied spectrum because it is also the simplest
Hydrogen has only ONE electron
But that ONE electron can be energized to many different orbitals ldquoexcited statesrdquo and will emit photons as it returns to its ldquoground staterdquo
Suppose an electron makes a transition from n = 3 to n = 2 What is the energy of the emitted photon
Energy = E3 ndash E2
E = 1207 eV ndash 1019 eV
E = 188 eV
What is the energy of an emitted photon if an electron makes a transition from n = 4 to n = 1
E = 1273 eVThe higher the energy of the photon the higher its frequency
E = hf
Each color has a different energy The further apart the lines the greater the difference in energy The closer the lines the less the difference in energy
Look at the spectrum for Hydrogen Which two lines have the least difference in energy Which two lines have the greatest difference in energy
Atomic SpectraAbsorption of an external source of
energy results in a transition to a higher energy level
bull A transition back to a lower level must release energy ndash in the form of a photon
bull The frequency of the emitted photon is determined by the difference in the energy levels
Ephoton = E2 ndash E1
Since E = hf the higher the energy the higher the frequency
bull Different frequencies are different colors of light or different types of EM Waves
The Hydrogen
AtomONE
electron
The frequency of the emitted photon is determined by the difference in the energy levelsEphoton = hf = E2 ndash E1
Now you try onehellipbull Get out your calculatorsbull The energized electron in Hydrogen makes a
transition from n = 3 with an energy of -15 eV down to its ground state where its energy is -136 eV
What is the frequency of the emitted photonbull Ephoton = E2 ndash E1 and Ephoton = hfbull Ephoton = -15 eV ndash (-136 eV) = 121 eVbull Ephoton = 121 eV = hf (h = 414 x 10-15 eVs )bull f = 121 eV divide 414 x 10-15 eVs = bull Frequency f = 292 x 1015 Hzbull Is this visible light Use c = f to find the
wavelengthbull wavelength = 102 x 10-7 = 102 nmbull This is NOT visible light- it is UV
Hydrogen EmissionThe energy in eV of the electron in a Hydrogen atom is given by
E =
1Find the energy of the electron at each orbit from n = 1 to n = 7
2 Find the Energy of each photon emitted (Ephoton = E) for these transitions from one orbit to another
4 to 1 5 to 2 6 to 3 7 to 4
3 to 1 4 to 2 5 to 3 6 to 4
2 to 1 3 to 2 4 to 3 5 to 4
3 Find the wavelength for each of those photons and determine what type of electromagnetic wave they are
2n
eV613
Light behaves like a wave AND like a particle
The first clear demonstration of the particle-like behavior of light was in
The Photoelectric Effect
Albert Einstein won the Nobel Prize in Physics for his study of the Photoelectric Effect
Shining light on a metal can liberate electrons from its surface
The light has to have enough energy (high enough frequency) for this effect to occur
The energy of the ldquophotoelectronsrdquo liberated from the surface depends on the frequency (the energy) of that incident light- NOT its intensity
Increasing the intensity of the light increases the number of photoelectrons emitted but not the energy of each photoelectron
When will Photoelectrons be producedPHet simulation
(Go to PHet website to explore the photoelectric effect simulation)
If no electrons are ejected you musthelliphellipincrease the frequency of the lightIf only a few electrons are ejected and you want
more your musthelliphellipincrease the intensity of the lightIf you want to increase the kinetic energy of the
electrons you musthelliphellipincrease the frequency of the light
hellip and the mathhellipUsing conservation of energyThe energy of the incident photon disappears
Where does it goFirst that energy must be used to liberate the
electron That energy is called the WORK FUNCTION WO Each kind of metal has its unique work function
Any extra energy is given appears in the electron as kinetic energy K
Photon Energy = Work function + Kinetic energy
E = Wo + K
ExamplePhoton energy = Wo + K
A photon with energy 32 eV strikes a metal surface with a work function of 18 eV What is the kinetic energy of the ejected photoelectrons
K = photon energy ndash Wo
K = 32 eV ndash 18 eV
K = 14 eV
ExamplePhoton energy = Wo + K
A photon with energy 28 eV strikes a metal surface If the kinetic energy of the ejected photoelectrons is 05 eV what is the work function of the metal
Wo = photon energy - K
Wo = 28 eV ndash 05 eV
Wo = 23 eV
hf = Wo + frac12 mv2
There is a minimum frequency called the ldquothreshold frequencyrdquo required to liberate an electron At the threshold frequency
Energy of photon = hfthreshold = Wo
That threshold photonrsquos wavelength is called the ldquocutoff wavelengthrdquo and can be found
using
c = f
Now you try some
If the cut-off wavelength for a particular metal is 320 nm what is the metalrsquos work function
First find the threshold frequency using c = f
Threshold frequency fo = 938 x 1014 Hz
Now find the work-function hfo = Wo
Be careful to use Planckrsquos constant with the correct units
h = 663 x 10-34Jmiddots or h = 414 x 10-15 eVmiddots
Wo = 622 x 10-19 J or Wo = 388 eV
What if a 450 nm light hit a surface with a work function of 236 eV What will be the kinetic energy of the photoelectron
First find the frequency of the 450 nm lightf = 667 x 1014 HzNow using conservation of energy
hf = Wo + Kinetic energySo K = hf ndash WoK = 040 eV How fast is the ejected electron movingK = frac12 mv2 m = 91 x 10-31 kg AND you have
to convert K back into Joules first
Using a Spectrometer to determine the identity of a elemental gas
1 The gas will not glow until it is energized Energy can be provided in the form of heat or by applying a high voltage The spectrum analysis power supply shown here provides high voltage
2 If you look at the glowing tube with just a diffraction grating the emission spectrum lines of color are visible
3 If you look at the glowing tube through a ldquospectrometerrdquo which contains a diffraction grating you can actually precisely measure the angles between the lines
4 Those angles allow you to precisely determine the wavelengths (or frequencies) of each of those colors
5 Since each element emits only certain wavelengths the gas can be identified
HydrogenThe emission spectrum of
Hydrogen is the most studied spectrum because it is also the simplest
Hydrogen has only ONE electron
But that ONE electron can be energized to many different orbitals ldquoexcited statesrdquo and will emit photons as it returns to its ldquoground staterdquo
Suppose an electron makes a transition from n = 3 to n = 2 What is the energy of the emitted photon
Energy = E3 ndash E2
E = 1207 eV ndash 1019 eV
E = 188 eV
What is the energy of an emitted photon if an electron makes a transition from n = 4 to n = 1
E = 1273 eVThe higher the energy of the photon the higher its frequency
E = hf
Each color has a different energy The further apart the lines the greater the difference in energy The closer the lines the less the difference in energy
Look at the spectrum for Hydrogen Which two lines have the least difference in energy Which two lines have the greatest difference in energy
Atomic SpectraAbsorption of an external source of
energy results in a transition to a higher energy level
bull A transition back to a lower level must release energy ndash in the form of a photon
bull The frequency of the emitted photon is determined by the difference in the energy levels
Ephoton = E2 ndash E1
Since E = hf the higher the energy the higher the frequency
bull Different frequencies are different colors of light or different types of EM Waves
The Hydrogen
AtomONE
electron
The frequency of the emitted photon is determined by the difference in the energy levelsEphoton = hf = E2 ndash E1
Now you try onehellipbull Get out your calculatorsbull The energized electron in Hydrogen makes a
transition from n = 3 with an energy of -15 eV down to its ground state where its energy is -136 eV
What is the frequency of the emitted photonbull Ephoton = E2 ndash E1 and Ephoton = hfbull Ephoton = -15 eV ndash (-136 eV) = 121 eVbull Ephoton = 121 eV = hf (h = 414 x 10-15 eVs )bull f = 121 eV divide 414 x 10-15 eVs = bull Frequency f = 292 x 1015 Hzbull Is this visible light Use c = f to find the
wavelengthbull wavelength = 102 x 10-7 = 102 nmbull This is NOT visible light- it is UV
Hydrogen EmissionThe energy in eV of the electron in a Hydrogen atom is given by
E =
1Find the energy of the electron at each orbit from n = 1 to n = 7
2 Find the Energy of each photon emitted (Ephoton = E) for these transitions from one orbit to another
4 to 1 5 to 2 6 to 3 7 to 4
3 to 1 4 to 2 5 to 3 6 to 4
2 to 1 3 to 2 4 to 3 5 to 4
3 Find the wavelength for each of those photons and determine what type of electromagnetic wave they are
2n
eV613
Light behaves like a wave AND like a particle
The first clear demonstration of the particle-like behavior of light was in
The Photoelectric Effect
Albert Einstein won the Nobel Prize in Physics for his study of the Photoelectric Effect
Shining light on a metal can liberate electrons from its surface
The light has to have enough energy (high enough frequency) for this effect to occur
The energy of the ldquophotoelectronsrdquo liberated from the surface depends on the frequency (the energy) of that incident light- NOT its intensity
Increasing the intensity of the light increases the number of photoelectrons emitted but not the energy of each photoelectron
When will Photoelectrons be producedPHet simulation
(Go to PHet website to explore the photoelectric effect simulation)
If no electrons are ejected you musthelliphellipincrease the frequency of the lightIf only a few electrons are ejected and you want
more your musthelliphellipincrease the intensity of the lightIf you want to increase the kinetic energy of the
electrons you musthelliphellipincrease the frequency of the light
hellip and the mathhellipUsing conservation of energyThe energy of the incident photon disappears
Where does it goFirst that energy must be used to liberate the
electron That energy is called the WORK FUNCTION WO Each kind of metal has its unique work function
Any extra energy is given appears in the electron as kinetic energy K
Photon Energy = Work function + Kinetic energy
E = Wo + K
ExamplePhoton energy = Wo + K
A photon with energy 32 eV strikes a metal surface with a work function of 18 eV What is the kinetic energy of the ejected photoelectrons
K = photon energy ndash Wo
K = 32 eV ndash 18 eV
K = 14 eV
ExamplePhoton energy = Wo + K
A photon with energy 28 eV strikes a metal surface If the kinetic energy of the ejected photoelectrons is 05 eV what is the work function of the metal
Wo = photon energy - K
Wo = 28 eV ndash 05 eV
Wo = 23 eV
hf = Wo + frac12 mv2
There is a minimum frequency called the ldquothreshold frequencyrdquo required to liberate an electron At the threshold frequency
Energy of photon = hfthreshold = Wo
That threshold photonrsquos wavelength is called the ldquocutoff wavelengthrdquo and can be found
using
c = f
Now you try some
If the cut-off wavelength for a particular metal is 320 nm what is the metalrsquos work function
First find the threshold frequency using c = f
Threshold frequency fo = 938 x 1014 Hz
Now find the work-function hfo = Wo
Be careful to use Planckrsquos constant with the correct units
h = 663 x 10-34Jmiddots or h = 414 x 10-15 eVmiddots
Wo = 622 x 10-19 J or Wo = 388 eV
What if a 450 nm light hit a surface with a work function of 236 eV What will be the kinetic energy of the photoelectron
First find the frequency of the 450 nm lightf = 667 x 1014 HzNow using conservation of energy
hf = Wo + Kinetic energySo K = hf ndash WoK = 040 eV How fast is the ejected electron movingK = frac12 mv2 m = 91 x 10-31 kg AND you have
to convert K back into Joules first
HydrogenThe emission spectrum of
Hydrogen is the most studied spectrum because it is also the simplest
Hydrogen has only ONE electron
But that ONE electron can be energized to many different orbitals ldquoexcited statesrdquo and will emit photons as it returns to its ldquoground staterdquo
Suppose an electron makes a transition from n = 3 to n = 2 What is the energy of the emitted photon
Energy = E3 ndash E2
E = 1207 eV ndash 1019 eV
E = 188 eV
What is the energy of an emitted photon if an electron makes a transition from n = 4 to n = 1
E = 1273 eVThe higher the energy of the photon the higher its frequency
E = hf
Each color has a different energy The further apart the lines the greater the difference in energy The closer the lines the less the difference in energy
Look at the spectrum for Hydrogen Which two lines have the least difference in energy Which two lines have the greatest difference in energy
Atomic SpectraAbsorption of an external source of
energy results in a transition to a higher energy level
bull A transition back to a lower level must release energy ndash in the form of a photon
bull The frequency of the emitted photon is determined by the difference in the energy levels
Ephoton = E2 ndash E1
Since E = hf the higher the energy the higher the frequency
bull Different frequencies are different colors of light or different types of EM Waves
The Hydrogen
AtomONE
electron
The frequency of the emitted photon is determined by the difference in the energy levelsEphoton = hf = E2 ndash E1
Now you try onehellipbull Get out your calculatorsbull The energized electron in Hydrogen makes a
transition from n = 3 with an energy of -15 eV down to its ground state where its energy is -136 eV
What is the frequency of the emitted photonbull Ephoton = E2 ndash E1 and Ephoton = hfbull Ephoton = -15 eV ndash (-136 eV) = 121 eVbull Ephoton = 121 eV = hf (h = 414 x 10-15 eVs )bull f = 121 eV divide 414 x 10-15 eVs = bull Frequency f = 292 x 1015 Hzbull Is this visible light Use c = f to find the
wavelengthbull wavelength = 102 x 10-7 = 102 nmbull This is NOT visible light- it is UV
Hydrogen EmissionThe energy in eV of the electron in a Hydrogen atom is given by
E =
1Find the energy of the electron at each orbit from n = 1 to n = 7
2 Find the Energy of each photon emitted (Ephoton = E) for these transitions from one orbit to another
4 to 1 5 to 2 6 to 3 7 to 4
3 to 1 4 to 2 5 to 3 6 to 4
2 to 1 3 to 2 4 to 3 5 to 4
3 Find the wavelength for each of those photons and determine what type of electromagnetic wave they are
2n
eV613
Light behaves like a wave AND like a particle
The first clear demonstration of the particle-like behavior of light was in
The Photoelectric Effect
Albert Einstein won the Nobel Prize in Physics for his study of the Photoelectric Effect
Shining light on a metal can liberate electrons from its surface
The light has to have enough energy (high enough frequency) for this effect to occur
The energy of the ldquophotoelectronsrdquo liberated from the surface depends on the frequency (the energy) of that incident light- NOT its intensity
Increasing the intensity of the light increases the number of photoelectrons emitted but not the energy of each photoelectron
When will Photoelectrons be producedPHet simulation
(Go to PHet website to explore the photoelectric effect simulation)
If no electrons are ejected you musthelliphellipincrease the frequency of the lightIf only a few electrons are ejected and you want
more your musthelliphellipincrease the intensity of the lightIf you want to increase the kinetic energy of the
electrons you musthelliphellipincrease the frequency of the light
hellip and the mathhellipUsing conservation of energyThe energy of the incident photon disappears
Where does it goFirst that energy must be used to liberate the
electron That energy is called the WORK FUNCTION WO Each kind of metal has its unique work function
Any extra energy is given appears in the electron as kinetic energy K
Photon Energy = Work function + Kinetic energy
E = Wo + K
ExamplePhoton energy = Wo + K
A photon with energy 32 eV strikes a metal surface with a work function of 18 eV What is the kinetic energy of the ejected photoelectrons
K = photon energy ndash Wo
K = 32 eV ndash 18 eV
K = 14 eV
ExamplePhoton energy = Wo + K
A photon with energy 28 eV strikes a metal surface If the kinetic energy of the ejected photoelectrons is 05 eV what is the work function of the metal
Wo = photon energy - K
Wo = 28 eV ndash 05 eV
Wo = 23 eV
hf = Wo + frac12 mv2
There is a minimum frequency called the ldquothreshold frequencyrdquo required to liberate an electron At the threshold frequency
Energy of photon = hfthreshold = Wo
That threshold photonrsquos wavelength is called the ldquocutoff wavelengthrdquo and can be found
using
c = f
Now you try some
If the cut-off wavelength for a particular metal is 320 nm what is the metalrsquos work function
First find the threshold frequency using c = f
Threshold frequency fo = 938 x 1014 Hz
Now find the work-function hfo = Wo
Be careful to use Planckrsquos constant with the correct units
h = 663 x 10-34Jmiddots or h = 414 x 10-15 eVmiddots
Wo = 622 x 10-19 J or Wo = 388 eV
What if a 450 nm light hit a surface with a work function of 236 eV What will be the kinetic energy of the photoelectron
First find the frequency of the 450 nm lightf = 667 x 1014 HzNow using conservation of energy
hf = Wo + Kinetic energySo K = hf ndash WoK = 040 eV How fast is the ejected electron movingK = frac12 mv2 m = 91 x 10-31 kg AND you have
to convert K back into Joules first
Suppose an electron makes a transition from n = 3 to n = 2 What is the energy of the emitted photon
Energy = E3 ndash E2
E = 1207 eV ndash 1019 eV
E = 188 eV
What is the energy of an emitted photon if an electron makes a transition from n = 4 to n = 1
E = 1273 eVThe higher the energy of the photon the higher its frequency
E = hf
Each color has a different energy The further apart the lines the greater the difference in energy The closer the lines the less the difference in energy
Look at the spectrum for Hydrogen Which two lines have the least difference in energy Which two lines have the greatest difference in energy
Atomic SpectraAbsorption of an external source of
energy results in a transition to a higher energy level
bull A transition back to a lower level must release energy ndash in the form of a photon
bull The frequency of the emitted photon is determined by the difference in the energy levels
Ephoton = E2 ndash E1
Since E = hf the higher the energy the higher the frequency
bull Different frequencies are different colors of light or different types of EM Waves
The Hydrogen
AtomONE
electron
The frequency of the emitted photon is determined by the difference in the energy levelsEphoton = hf = E2 ndash E1
Now you try onehellipbull Get out your calculatorsbull The energized electron in Hydrogen makes a
transition from n = 3 with an energy of -15 eV down to its ground state where its energy is -136 eV
What is the frequency of the emitted photonbull Ephoton = E2 ndash E1 and Ephoton = hfbull Ephoton = -15 eV ndash (-136 eV) = 121 eVbull Ephoton = 121 eV = hf (h = 414 x 10-15 eVs )bull f = 121 eV divide 414 x 10-15 eVs = bull Frequency f = 292 x 1015 Hzbull Is this visible light Use c = f to find the
wavelengthbull wavelength = 102 x 10-7 = 102 nmbull This is NOT visible light- it is UV
Hydrogen EmissionThe energy in eV of the electron in a Hydrogen atom is given by
E =
1Find the energy of the electron at each orbit from n = 1 to n = 7
2 Find the Energy of each photon emitted (Ephoton = E) for these transitions from one orbit to another
4 to 1 5 to 2 6 to 3 7 to 4
3 to 1 4 to 2 5 to 3 6 to 4
2 to 1 3 to 2 4 to 3 5 to 4
3 Find the wavelength for each of those photons and determine what type of electromagnetic wave they are
2n
eV613
Light behaves like a wave AND like a particle
The first clear demonstration of the particle-like behavior of light was in
The Photoelectric Effect
Albert Einstein won the Nobel Prize in Physics for his study of the Photoelectric Effect
Shining light on a metal can liberate electrons from its surface
The light has to have enough energy (high enough frequency) for this effect to occur
The energy of the ldquophotoelectronsrdquo liberated from the surface depends on the frequency (the energy) of that incident light- NOT its intensity
Increasing the intensity of the light increases the number of photoelectrons emitted but not the energy of each photoelectron
When will Photoelectrons be producedPHet simulation
(Go to PHet website to explore the photoelectric effect simulation)
If no electrons are ejected you musthelliphellipincrease the frequency of the lightIf only a few electrons are ejected and you want
more your musthelliphellipincrease the intensity of the lightIf you want to increase the kinetic energy of the
electrons you musthelliphellipincrease the frequency of the light
hellip and the mathhellipUsing conservation of energyThe energy of the incident photon disappears
Where does it goFirst that energy must be used to liberate the
electron That energy is called the WORK FUNCTION WO Each kind of metal has its unique work function
Any extra energy is given appears in the electron as kinetic energy K
Photon Energy = Work function + Kinetic energy
E = Wo + K
ExamplePhoton energy = Wo + K
A photon with energy 32 eV strikes a metal surface with a work function of 18 eV What is the kinetic energy of the ejected photoelectrons
K = photon energy ndash Wo
K = 32 eV ndash 18 eV
K = 14 eV
ExamplePhoton energy = Wo + K
A photon with energy 28 eV strikes a metal surface If the kinetic energy of the ejected photoelectrons is 05 eV what is the work function of the metal
Wo = photon energy - K
Wo = 28 eV ndash 05 eV
Wo = 23 eV
hf = Wo + frac12 mv2
There is a minimum frequency called the ldquothreshold frequencyrdquo required to liberate an electron At the threshold frequency
Energy of photon = hfthreshold = Wo
That threshold photonrsquos wavelength is called the ldquocutoff wavelengthrdquo and can be found
using
c = f
Now you try some
If the cut-off wavelength for a particular metal is 320 nm what is the metalrsquos work function
First find the threshold frequency using c = f
Threshold frequency fo = 938 x 1014 Hz
Now find the work-function hfo = Wo
Be careful to use Planckrsquos constant with the correct units
h = 663 x 10-34Jmiddots or h = 414 x 10-15 eVmiddots
Wo = 622 x 10-19 J or Wo = 388 eV
What if a 450 nm light hit a surface with a work function of 236 eV What will be the kinetic energy of the photoelectron
First find the frequency of the 450 nm lightf = 667 x 1014 HzNow using conservation of energy
hf = Wo + Kinetic energySo K = hf ndash WoK = 040 eV How fast is the ejected electron movingK = frac12 mv2 m = 91 x 10-31 kg AND you have
to convert K back into Joules first
Each color has a different energy The further apart the lines the greater the difference in energy The closer the lines the less the difference in energy
Look at the spectrum for Hydrogen Which two lines have the least difference in energy Which two lines have the greatest difference in energy
Atomic SpectraAbsorption of an external source of
energy results in a transition to a higher energy level
bull A transition back to a lower level must release energy ndash in the form of a photon
bull The frequency of the emitted photon is determined by the difference in the energy levels
Ephoton = E2 ndash E1
Since E = hf the higher the energy the higher the frequency
bull Different frequencies are different colors of light or different types of EM Waves
The Hydrogen
AtomONE
electron
The frequency of the emitted photon is determined by the difference in the energy levelsEphoton = hf = E2 ndash E1
Now you try onehellipbull Get out your calculatorsbull The energized electron in Hydrogen makes a
transition from n = 3 with an energy of -15 eV down to its ground state where its energy is -136 eV
What is the frequency of the emitted photonbull Ephoton = E2 ndash E1 and Ephoton = hfbull Ephoton = -15 eV ndash (-136 eV) = 121 eVbull Ephoton = 121 eV = hf (h = 414 x 10-15 eVs )bull f = 121 eV divide 414 x 10-15 eVs = bull Frequency f = 292 x 1015 Hzbull Is this visible light Use c = f to find the
wavelengthbull wavelength = 102 x 10-7 = 102 nmbull This is NOT visible light- it is UV
Hydrogen EmissionThe energy in eV of the electron in a Hydrogen atom is given by
E =
1Find the energy of the electron at each orbit from n = 1 to n = 7
2 Find the Energy of each photon emitted (Ephoton = E) for these transitions from one orbit to another
4 to 1 5 to 2 6 to 3 7 to 4
3 to 1 4 to 2 5 to 3 6 to 4
2 to 1 3 to 2 4 to 3 5 to 4
3 Find the wavelength for each of those photons and determine what type of electromagnetic wave they are
2n
eV613
Light behaves like a wave AND like a particle
The first clear demonstration of the particle-like behavior of light was in
The Photoelectric Effect
Albert Einstein won the Nobel Prize in Physics for his study of the Photoelectric Effect
Shining light on a metal can liberate electrons from its surface
The light has to have enough energy (high enough frequency) for this effect to occur
The energy of the ldquophotoelectronsrdquo liberated from the surface depends on the frequency (the energy) of that incident light- NOT its intensity
Increasing the intensity of the light increases the number of photoelectrons emitted but not the energy of each photoelectron
When will Photoelectrons be producedPHet simulation
(Go to PHet website to explore the photoelectric effect simulation)
If no electrons are ejected you musthelliphellipincrease the frequency of the lightIf only a few electrons are ejected and you want
more your musthelliphellipincrease the intensity of the lightIf you want to increase the kinetic energy of the
electrons you musthelliphellipincrease the frequency of the light
hellip and the mathhellipUsing conservation of energyThe energy of the incident photon disappears
Where does it goFirst that energy must be used to liberate the
electron That energy is called the WORK FUNCTION WO Each kind of metal has its unique work function
Any extra energy is given appears in the electron as kinetic energy K
Photon Energy = Work function + Kinetic energy
E = Wo + K
ExamplePhoton energy = Wo + K
A photon with energy 32 eV strikes a metal surface with a work function of 18 eV What is the kinetic energy of the ejected photoelectrons
K = photon energy ndash Wo
K = 32 eV ndash 18 eV
K = 14 eV
ExamplePhoton energy = Wo + K
A photon with energy 28 eV strikes a metal surface If the kinetic energy of the ejected photoelectrons is 05 eV what is the work function of the metal
Wo = photon energy - K
Wo = 28 eV ndash 05 eV
Wo = 23 eV
hf = Wo + frac12 mv2
There is a minimum frequency called the ldquothreshold frequencyrdquo required to liberate an electron At the threshold frequency
Energy of photon = hfthreshold = Wo
That threshold photonrsquos wavelength is called the ldquocutoff wavelengthrdquo and can be found
using
c = f
Now you try some
If the cut-off wavelength for a particular metal is 320 nm what is the metalrsquos work function
First find the threshold frequency using c = f
Threshold frequency fo = 938 x 1014 Hz
Now find the work-function hfo = Wo
Be careful to use Planckrsquos constant with the correct units
h = 663 x 10-34Jmiddots or h = 414 x 10-15 eVmiddots
Wo = 622 x 10-19 J or Wo = 388 eV
What if a 450 nm light hit a surface with a work function of 236 eV What will be the kinetic energy of the photoelectron
First find the frequency of the 450 nm lightf = 667 x 1014 HzNow using conservation of energy
hf = Wo + Kinetic energySo K = hf ndash WoK = 040 eV How fast is the ejected electron movingK = frac12 mv2 m = 91 x 10-31 kg AND you have
to convert K back into Joules first
Atomic SpectraAbsorption of an external source of
energy results in a transition to a higher energy level
bull A transition back to a lower level must release energy ndash in the form of a photon
bull The frequency of the emitted photon is determined by the difference in the energy levels
Ephoton = E2 ndash E1
Since E = hf the higher the energy the higher the frequency
bull Different frequencies are different colors of light or different types of EM Waves
The Hydrogen
AtomONE
electron
The frequency of the emitted photon is determined by the difference in the energy levelsEphoton = hf = E2 ndash E1
Now you try onehellipbull Get out your calculatorsbull The energized electron in Hydrogen makes a
transition from n = 3 with an energy of -15 eV down to its ground state where its energy is -136 eV
What is the frequency of the emitted photonbull Ephoton = E2 ndash E1 and Ephoton = hfbull Ephoton = -15 eV ndash (-136 eV) = 121 eVbull Ephoton = 121 eV = hf (h = 414 x 10-15 eVs )bull f = 121 eV divide 414 x 10-15 eVs = bull Frequency f = 292 x 1015 Hzbull Is this visible light Use c = f to find the
wavelengthbull wavelength = 102 x 10-7 = 102 nmbull This is NOT visible light- it is UV
Hydrogen EmissionThe energy in eV of the electron in a Hydrogen atom is given by
E =
1Find the energy of the electron at each orbit from n = 1 to n = 7
2 Find the Energy of each photon emitted (Ephoton = E) for these transitions from one orbit to another
4 to 1 5 to 2 6 to 3 7 to 4
3 to 1 4 to 2 5 to 3 6 to 4
2 to 1 3 to 2 4 to 3 5 to 4
3 Find the wavelength for each of those photons and determine what type of electromagnetic wave they are
2n
eV613
Light behaves like a wave AND like a particle
The first clear demonstration of the particle-like behavior of light was in
The Photoelectric Effect
Albert Einstein won the Nobel Prize in Physics for his study of the Photoelectric Effect
Shining light on a metal can liberate electrons from its surface
The light has to have enough energy (high enough frequency) for this effect to occur
The energy of the ldquophotoelectronsrdquo liberated from the surface depends on the frequency (the energy) of that incident light- NOT its intensity
Increasing the intensity of the light increases the number of photoelectrons emitted but not the energy of each photoelectron
When will Photoelectrons be producedPHet simulation
(Go to PHet website to explore the photoelectric effect simulation)
If no electrons are ejected you musthelliphellipincrease the frequency of the lightIf only a few electrons are ejected and you want
more your musthelliphellipincrease the intensity of the lightIf you want to increase the kinetic energy of the
electrons you musthelliphellipincrease the frequency of the light
hellip and the mathhellipUsing conservation of energyThe energy of the incident photon disappears
Where does it goFirst that energy must be used to liberate the
electron That energy is called the WORK FUNCTION WO Each kind of metal has its unique work function
Any extra energy is given appears in the electron as kinetic energy K
Photon Energy = Work function + Kinetic energy
E = Wo + K
ExamplePhoton energy = Wo + K
A photon with energy 32 eV strikes a metal surface with a work function of 18 eV What is the kinetic energy of the ejected photoelectrons
K = photon energy ndash Wo
K = 32 eV ndash 18 eV
K = 14 eV
ExamplePhoton energy = Wo + K
A photon with energy 28 eV strikes a metal surface If the kinetic energy of the ejected photoelectrons is 05 eV what is the work function of the metal
Wo = photon energy - K
Wo = 28 eV ndash 05 eV
Wo = 23 eV
hf = Wo + frac12 mv2
There is a minimum frequency called the ldquothreshold frequencyrdquo required to liberate an electron At the threshold frequency
Energy of photon = hfthreshold = Wo
That threshold photonrsquos wavelength is called the ldquocutoff wavelengthrdquo and can be found
using
c = f
Now you try some
If the cut-off wavelength for a particular metal is 320 nm what is the metalrsquos work function
First find the threshold frequency using c = f
Threshold frequency fo = 938 x 1014 Hz
Now find the work-function hfo = Wo
Be careful to use Planckrsquos constant with the correct units
h = 663 x 10-34Jmiddots or h = 414 x 10-15 eVmiddots
Wo = 622 x 10-19 J or Wo = 388 eV
What if a 450 nm light hit a surface with a work function of 236 eV What will be the kinetic energy of the photoelectron
First find the frequency of the 450 nm lightf = 667 x 1014 HzNow using conservation of energy
hf = Wo + Kinetic energySo K = hf ndash WoK = 040 eV How fast is the ejected electron movingK = frac12 mv2 m = 91 x 10-31 kg AND you have
to convert K back into Joules first
The Hydrogen
AtomONE
electron
The frequency of the emitted photon is determined by the difference in the energy levelsEphoton = hf = E2 ndash E1
Now you try onehellipbull Get out your calculatorsbull The energized electron in Hydrogen makes a
transition from n = 3 with an energy of -15 eV down to its ground state where its energy is -136 eV
What is the frequency of the emitted photonbull Ephoton = E2 ndash E1 and Ephoton = hfbull Ephoton = -15 eV ndash (-136 eV) = 121 eVbull Ephoton = 121 eV = hf (h = 414 x 10-15 eVs )bull f = 121 eV divide 414 x 10-15 eVs = bull Frequency f = 292 x 1015 Hzbull Is this visible light Use c = f to find the
wavelengthbull wavelength = 102 x 10-7 = 102 nmbull This is NOT visible light- it is UV
Hydrogen EmissionThe energy in eV of the electron in a Hydrogen atom is given by
E =
1Find the energy of the electron at each orbit from n = 1 to n = 7
2 Find the Energy of each photon emitted (Ephoton = E) for these transitions from one orbit to another
4 to 1 5 to 2 6 to 3 7 to 4
3 to 1 4 to 2 5 to 3 6 to 4
2 to 1 3 to 2 4 to 3 5 to 4
3 Find the wavelength for each of those photons and determine what type of electromagnetic wave they are
2n
eV613
Light behaves like a wave AND like a particle
The first clear demonstration of the particle-like behavior of light was in
The Photoelectric Effect
Albert Einstein won the Nobel Prize in Physics for his study of the Photoelectric Effect
Shining light on a metal can liberate electrons from its surface
The light has to have enough energy (high enough frequency) for this effect to occur
The energy of the ldquophotoelectronsrdquo liberated from the surface depends on the frequency (the energy) of that incident light- NOT its intensity
Increasing the intensity of the light increases the number of photoelectrons emitted but not the energy of each photoelectron
When will Photoelectrons be producedPHet simulation
(Go to PHet website to explore the photoelectric effect simulation)
If no electrons are ejected you musthelliphellipincrease the frequency of the lightIf only a few electrons are ejected and you want
more your musthelliphellipincrease the intensity of the lightIf you want to increase the kinetic energy of the
electrons you musthelliphellipincrease the frequency of the light
hellip and the mathhellipUsing conservation of energyThe energy of the incident photon disappears
Where does it goFirst that energy must be used to liberate the
electron That energy is called the WORK FUNCTION WO Each kind of metal has its unique work function
Any extra energy is given appears in the electron as kinetic energy K
Photon Energy = Work function + Kinetic energy
E = Wo + K
ExamplePhoton energy = Wo + K
A photon with energy 32 eV strikes a metal surface with a work function of 18 eV What is the kinetic energy of the ejected photoelectrons
K = photon energy ndash Wo
K = 32 eV ndash 18 eV
K = 14 eV
ExamplePhoton energy = Wo + K
A photon with energy 28 eV strikes a metal surface If the kinetic energy of the ejected photoelectrons is 05 eV what is the work function of the metal
Wo = photon energy - K
Wo = 28 eV ndash 05 eV
Wo = 23 eV
hf = Wo + frac12 mv2
There is a minimum frequency called the ldquothreshold frequencyrdquo required to liberate an electron At the threshold frequency
Energy of photon = hfthreshold = Wo
That threshold photonrsquos wavelength is called the ldquocutoff wavelengthrdquo and can be found
using
c = f
Now you try some
If the cut-off wavelength for a particular metal is 320 nm what is the metalrsquos work function
First find the threshold frequency using c = f
Threshold frequency fo = 938 x 1014 Hz
Now find the work-function hfo = Wo
Be careful to use Planckrsquos constant with the correct units
h = 663 x 10-34Jmiddots or h = 414 x 10-15 eVmiddots
Wo = 622 x 10-19 J or Wo = 388 eV
What if a 450 nm light hit a surface with a work function of 236 eV What will be the kinetic energy of the photoelectron
First find the frequency of the 450 nm lightf = 667 x 1014 HzNow using conservation of energy
hf = Wo + Kinetic energySo K = hf ndash WoK = 040 eV How fast is the ejected electron movingK = frac12 mv2 m = 91 x 10-31 kg AND you have
to convert K back into Joules first
Now you try onehellipbull Get out your calculatorsbull The energized electron in Hydrogen makes a
transition from n = 3 with an energy of -15 eV down to its ground state where its energy is -136 eV
What is the frequency of the emitted photonbull Ephoton = E2 ndash E1 and Ephoton = hfbull Ephoton = -15 eV ndash (-136 eV) = 121 eVbull Ephoton = 121 eV = hf (h = 414 x 10-15 eVs )bull f = 121 eV divide 414 x 10-15 eVs = bull Frequency f = 292 x 1015 Hzbull Is this visible light Use c = f to find the
wavelengthbull wavelength = 102 x 10-7 = 102 nmbull This is NOT visible light- it is UV
Hydrogen EmissionThe energy in eV of the electron in a Hydrogen atom is given by
E =
1Find the energy of the electron at each orbit from n = 1 to n = 7
2 Find the Energy of each photon emitted (Ephoton = E) for these transitions from one orbit to another
4 to 1 5 to 2 6 to 3 7 to 4
3 to 1 4 to 2 5 to 3 6 to 4
2 to 1 3 to 2 4 to 3 5 to 4
3 Find the wavelength for each of those photons and determine what type of electromagnetic wave they are
2n
eV613
Light behaves like a wave AND like a particle
The first clear demonstration of the particle-like behavior of light was in
The Photoelectric Effect
Albert Einstein won the Nobel Prize in Physics for his study of the Photoelectric Effect
Shining light on a metal can liberate electrons from its surface
The light has to have enough energy (high enough frequency) for this effect to occur
The energy of the ldquophotoelectronsrdquo liberated from the surface depends on the frequency (the energy) of that incident light- NOT its intensity
Increasing the intensity of the light increases the number of photoelectrons emitted but not the energy of each photoelectron
When will Photoelectrons be producedPHet simulation
(Go to PHet website to explore the photoelectric effect simulation)
If no electrons are ejected you musthelliphellipincrease the frequency of the lightIf only a few electrons are ejected and you want
more your musthelliphellipincrease the intensity of the lightIf you want to increase the kinetic energy of the
electrons you musthelliphellipincrease the frequency of the light
hellip and the mathhellipUsing conservation of energyThe energy of the incident photon disappears
Where does it goFirst that energy must be used to liberate the
electron That energy is called the WORK FUNCTION WO Each kind of metal has its unique work function
Any extra energy is given appears in the electron as kinetic energy K
Photon Energy = Work function + Kinetic energy
E = Wo + K
ExamplePhoton energy = Wo + K
A photon with energy 32 eV strikes a metal surface with a work function of 18 eV What is the kinetic energy of the ejected photoelectrons
K = photon energy ndash Wo
K = 32 eV ndash 18 eV
K = 14 eV
ExamplePhoton energy = Wo + K
A photon with energy 28 eV strikes a metal surface If the kinetic energy of the ejected photoelectrons is 05 eV what is the work function of the metal
Wo = photon energy - K
Wo = 28 eV ndash 05 eV
Wo = 23 eV
hf = Wo + frac12 mv2
There is a minimum frequency called the ldquothreshold frequencyrdquo required to liberate an electron At the threshold frequency
Energy of photon = hfthreshold = Wo
That threshold photonrsquos wavelength is called the ldquocutoff wavelengthrdquo and can be found
using
c = f
Now you try some
If the cut-off wavelength for a particular metal is 320 nm what is the metalrsquos work function
First find the threshold frequency using c = f
Threshold frequency fo = 938 x 1014 Hz
Now find the work-function hfo = Wo
Be careful to use Planckrsquos constant with the correct units
h = 663 x 10-34Jmiddots or h = 414 x 10-15 eVmiddots
Wo = 622 x 10-19 J or Wo = 388 eV
What if a 450 nm light hit a surface with a work function of 236 eV What will be the kinetic energy of the photoelectron
First find the frequency of the 450 nm lightf = 667 x 1014 HzNow using conservation of energy
hf = Wo + Kinetic energySo K = hf ndash WoK = 040 eV How fast is the ejected electron movingK = frac12 mv2 m = 91 x 10-31 kg AND you have
to convert K back into Joules first
Hydrogen EmissionThe energy in eV of the electron in a Hydrogen atom is given by
E =
1Find the energy of the electron at each orbit from n = 1 to n = 7
2 Find the Energy of each photon emitted (Ephoton = E) for these transitions from one orbit to another
4 to 1 5 to 2 6 to 3 7 to 4
3 to 1 4 to 2 5 to 3 6 to 4
2 to 1 3 to 2 4 to 3 5 to 4
3 Find the wavelength for each of those photons and determine what type of electromagnetic wave they are
2n
eV613
Light behaves like a wave AND like a particle
The first clear demonstration of the particle-like behavior of light was in
The Photoelectric Effect
Albert Einstein won the Nobel Prize in Physics for his study of the Photoelectric Effect
Shining light on a metal can liberate electrons from its surface
The light has to have enough energy (high enough frequency) for this effect to occur
The energy of the ldquophotoelectronsrdquo liberated from the surface depends on the frequency (the energy) of that incident light- NOT its intensity
Increasing the intensity of the light increases the number of photoelectrons emitted but not the energy of each photoelectron
When will Photoelectrons be producedPHet simulation
(Go to PHet website to explore the photoelectric effect simulation)
If no electrons are ejected you musthelliphellipincrease the frequency of the lightIf only a few electrons are ejected and you want
more your musthelliphellipincrease the intensity of the lightIf you want to increase the kinetic energy of the
electrons you musthelliphellipincrease the frequency of the light
hellip and the mathhellipUsing conservation of energyThe energy of the incident photon disappears
Where does it goFirst that energy must be used to liberate the
electron That energy is called the WORK FUNCTION WO Each kind of metal has its unique work function
Any extra energy is given appears in the electron as kinetic energy K
Photon Energy = Work function + Kinetic energy
E = Wo + K
ExamplePhoton energy = Wo + K
A photon with energy 32 eV strikes a metal surface with a work function of 18 eV What is the kinetic energy of the ejected photoelectrons
K = photon energy ndash Wo
K = 32 eV ndash 18 eV
K = 14 eV
ExamplePhoton energy = Wo + K
A photon with energy 28 eV strikes a metal surface If the kinetic energy of the ejected photoelectrons is 05 eV what is the work function of the metal
Wo = photon energy - K
Wo = 28 eV ndash 05 eV
Wo = 23 eV
hf = Wo + frac12 mv2
There is a minimum frequency called the ldquothreshold frequencyrdquo required to liberate an electron At the threshold frequency
Energy of photon = hfthreshold = Wo
That threshold photonrsquos wavelength is called the ldquocutoff wavelengthrdquo and can be found
using
c = f
Now you try some
If the cut-off wavelength for a particular metal is 320 nm what is the metalrsquos work function
First find the threshold frequency using c = f
Threshold frequency fo = 938 x 1014 Hz
Now find the work-function hfo = Wo
Be careful to use Planckrsquos constant with the correct units
h = 663 x 10-34Jmiddots or h = 414 x 10-15 eVmiddots
Wo = 622 x 10-19 J or Wo = 388 eV
What if a 450 nm light hit a surface with a work function of 236 eV What will be the kinetic energy of the photoelectron
First find the frequency of the 450 nm lightf = 667 x 1014 HzNow using conservation of energy
hf = Wo + Kinetic energySo K = hf ndash WoK = 040 eV How fast is the ejected electron movingK = frac12 mv2 m = 91 x 10-31 kg AND you have
to convert K back into Joules first
Light behaves like a wave AND like a particle
The first clear demonstration of the particle-like behavior of light was in
The Photoelectric Effect
Albert Einstein won the Nobel Prize in Physics for his study of the Photoelectric Effect
Shining light on a metal can liberate electrons from its surface
The light has to have enough energy (high enough frequency) for this effect to occur
The energy of the ldquophotoelectronsrdquo liberated from the surface depends on the frequency (the energy) of that incident light- NOT its intensity
Increasing the intensity of the light increases the number of photoelectrons emitted but not the energy of each photoelectron
When will Photoelectrons be producedPHet simulation
(Go to PHet website to explore the photoelectric effect simulation)
If no electrons are ejected you musthelliphellipincrease the frequency of the lightIf only a few electrons are ejected and you want
more your musthelliphellipincrease the intensity of the lightIf you want to increase the kinetic energy of the
electrons you musthelliphellipincrease the frequency of the light
hellip and the mathhellipUsing conservation of energyThe energy of the incident photon disappears
Where does it goFirst that energy must be used to liberate the
electron That energy is called the WORK FUNCTION WO Each kind of metal has its unique work function
Any extra energy is given appears in the electron as kinetic energy K
Photon Energy = Work function + Kinetic energy
E = Wo + K
ExamplePhoton energy = Wo + K
A photon with energy 32 eV strikes a metal surface with a work function of 18 eV What is the kinetic energy of the ejected photoelectrons
K = photon energy ndash Wo
K = 32 eV ndash 18 eV
K = 14 eV
ExamplePhoton energy = Wo + K
A photon with energy 28 eV strikes a metal surface If the kinetic energy of the ejected photoelectrons is 05 eV what is the work function of the metal
Wo = photon energy - K
Wo = 28 eV ndash 05 eV
Wo = 23 eV
hf = Wo + frac12 mv2
There is a minimum frequency called the ldquothreshold frequencyrdquo required to liberate an electron At the threshold frequency
Energy of photon = hfthreshold = Wo
That threshold photonrsquos wavelength is called the ldquocutoff wavelengthrdquo and can be found
using
c = f
Now you try some
If the cut-off wavelength for a particular metal is 320 nm what is the metalrsquos work function
First find the threshold frequency using c = f
Threshold frequency fo = 938 x 1014 Hz
Now find the work-function hfo = Wo
Be careful to use Planckrsquos constant with the correct units
h = 663 x 10-34Jmiddots or h = 414 x 10-15 eVmiddots
Wo = 622 x 10-19 J or Wo = 388 eV
What if a 450 nm light hit a surface with a work function of 236 eV What will be the kinetic energy of the photoelectron
First find the frequency of the 450 nm lightf = 667 x 1014 HzNow using conservation of energy
hf = Wo + Kinetic energySo K = hf ndash WoK = 040 eV How fast is the ejected electron movingK = frac12 mv2 m = 91 x 10-31 kg AND you have
to convert K back into Joules first
Shining light on a metal can liberate electrons from its surface
The light has to have enough energy (high enough frequency) for this effect to occur
The energy of the ldquophotoelectronsrdquo liberated from the surface depends on the frequency (the energy) of that incident light- NOT its intensity
Increasing the intensity of the light increases the number of photoelectrons emitted but not the energy of each photoelectron
When will Photoelectrons be producedPHet simulation
(Go to PHet website to explore the photoelectric effect simulation)
If no electrons are ejected you musthelliphellipincrease the frequency of the lightIf only a few electrons are ejected and you want
more your musthelliphellipincrease the intensity of the lightIf you want to increase the kinetic energy of the
electrons you musthelliphellipincrease the frequency of the light
hellip and the mathhellipUsing conservation of energyThe energy of the incident photon disappears
Where does it goFirst that energy must be used to liberate the
electron That energy is called the WORK FUNCTION WO Each kind of metal has its unique work function
Any extra energy is given appears in the electron as kinetic energy K
Photon Energy = Work function + Kinetic energy
E = Wo + K
ExamplePhoton energy = Wo + K
A photon with energy 32 eV strikes a metal surface with a work function of 18 eV What is the kinetic energy of the ejected photoelectrons
K = photon energy ndash Wo
K = 32 eV ndash 18 eV
K = 14 eV
ExamplePhoton energy = Wo + K
A photon with energy 28 eV strikes a metal surface If the kinetic energy of the ejected photoelectrons is 05 eV what is the work function of the metal
Wo = photon energy - K
Wo = 28 eV ndash 05 eV
Wo = 23 eV
hf = Wo + frac12 mv2
There is a minimum frequency called the ldquothreshold frequencyrdquo required to liberate an electron At the threshold frequency
Energy of photon = hfthreshold = Wo
That threshold photonrsquos wavelength is called the ldquocutoff wavelengthrdquo and can be found
using
c = f
Now you try some
If the cut-off wavelength for a particular metal is 320 nm what is the metalrsquos work function
First find the threshold frequency using c = f
Threshold frequency fo = 938 x 1014 Hz
Now find the work-function hfo = Wo
Be careful to use Planckrsquos constant with the correct units
h = 663 x 10-34Jmiddots or h = 414 x 10-15 eVmiddots
Wo = 622 x 10-19 J or Wo = 388 eV
What if a 450 nm light hit a surface with a work function of 236 eV What will be the kinetic energy of the photoelectron
First find the frequency of the 450 nm lightf = 667 x 1014 HzNow using conservation of energy
hf = Wo + Kinetic energySo K = hf ndash WoK = 040 eV How fast is the ejected electron movingK = frac12 mv2 m = 91 x 10-31 kg AND you have
to convert K back into Joules first
When will Photoelectrons be producedPHet simulation
(Go to PHet website to explore the photoelectric effect simulation)
If no electrons are ejected you musthelliphellipincrease the frequency of the lightIf only a few electrons are ejected and you want
more your musthelliphellipincrease the intensity of the lightIf you want to increase the kinetic energy of the
electrons you musthelliphellipincrease the frequency of the light
hellip and the mathhellipUsing conservation of energyThe energy of the incident photon disappears
Where does it goFirst that energy must be used to liberate the
electron That energy is called the WORK FUNCTION WO Each kind of metal has its unique work function
Any extra energy is given appears in the electron as kinetic energy K
Photon Energy = Work function + Kinetic energy
E = Wo + K
ExamplePhoton energy = Wo + K
A photon with energy 32 eV strikes a metal surface with a work function of 18 eV What is the kinetic energy of the ejected photoelectrons
K = photon energy ndash Wo
K = 32 eV ndash 18 eV
K = 14 eV
ExamplePhoton energy = Wo + K
A photon with energy 28 eV strikes a metal surface If the kinetic energy of the ejected photoelectrons is 05 eV what is the work function of the metal
Wo = photon energy - K
Wo = 28 eV ndash 05 eV
Wo = 23 eV
hf = Wo + frac12 mv2
There is a minimum frequency called the ldquothreshold frequencyrdquo required to liberate an electron At the threshold frequency
Energy of photon = hfthreshold = Wo
That threshold photonrsquos wavelength is called the ldquocutoff wavelengthrdquo and can be found
using
c = f
Now you try some
If the cut-off wavelength for a particular metal is 320 nm what is the metalrsquos work function
First find the threshold frequency using c = f
Threshold frequency fo = 938 x 1014 Hz
Now find the work-function hfo = Wo
Be careful to use Planckrsquos constant with the correct units
h = 663 x 10-34Jmiddots or h = 414 x 10-15 eVmiddots
Wo = 622 x 10-19 J or Wo = 388 eV
What if a 450 nm light hit a surface with a work function of 236 eV What will be the kinetic energy of the photoelectron
First find the frequency of the 450 nm lightf = 667 x 1014 HzNow using conservation of energy
hf = Wo + Kinetic energySo K = hf ndash WoK = 040 eV How fast is the ejected electron movingK = frac12 mv2 m = 91 x 10-31 kg AND you have
to convert K back into Joules first
If no electrons are ejected you musthelliphellipincrease the frequency of the lightIf only a few electrons are ejected and you want
more your musthelliphellipincrease the intensity of the lightIf you want to increase the kinetic energy of the
electrons you musthelliphellipincrease the frequency of the light
hellip and the mathhellipUsing conservation of energyThe energy of the incident photon disappears
Where does it goFirst that energy must be used to liberate the
electron That energy is called the WORK FUNCTION WO Each kind of metal has its unique work function
Any extra energy is given appears in the electron as kinetic energy K
Photon Energy = Work function + Kinetic energy
E = Wo + K
ExamplePhoton energy = Wo + K
A photon with energy 32 eV strikes a metal surface with a work function of 18 eV What is the kinetic energy of the ejected photoelectrons
K = photon energy ndash Wo
K = 32 eV ndash 18 eV
K = 14 eV
ExamplePhoton energy = Wo + K
A photon with energy 28 eV strikes a metal surface If the kinetic energy of the ejected photoelectrons is 05 eV what is the work function of the metal
Wo = photon energy - K
Wo = 28 eV ndash 05 eV
Wo = 23 eV
hf = Wo + frac12 mv2
There is a minimum frequency called the ldquothreshold frequencyrdquo required to liberate an electron At the threshold frequency
Energy of photon = hfthreshold = Wo
That threshold photonrsquos wavelength is called the ldquocutoff wavelengthrdquo and can be found
using
c = f
Now you try some
If the cut-off wavelength for a particular metal is 320 nm what is the metalrsquos work function
First find the threshold frequency using c = f
Threshold frequency fo = 938 x 1014 Hz
Now find the work-function hfo = Wo
Be careful to use Planckrsquos constant with the correct units
h = 663 x 10-34Jmiddots or h = 414 x 10-15 eVmiddots
Wo = 622 x 10-19 J or Wo = 388 eV
What if a 450 nm light hit a surface with a work function of 236 eV What will be the kinetic energy of the photoelectron
First find the frequency of the 450 nm lightf = 667 x 1014 HzNow using conservation of energy
hf = Wo + Kinetic energySo K = hf ndash WoK = 040 eV How fast is the ejected electron movingK = frac12 mv2 m = 91 x 10-31 kg AND you have
to convert K back into Joules first
hellip and the mathhellipUsing conservation of energyThe energy of the incident photon disappears
Where does it goFirst that energy must be used to liberate the
electron That energy is called the WORK FUNCTION WO Each kind of metal has its unique work function
Any extra energy is given appears in the electron as kinetic energy K
Photon Energy = Work function + Kinetic energy
E = Wo + K
ExamplePhoton energy = Wo + K
A photon with energy 32 eV strikes a metal surface with a work function of 18 eV What is the kinetic energy of the ejected photoelectrons
K = photon energy ndash Wo
K = 32 eV ndash 18 eV
K = 14 eV
ExamplePhoton energy = Wo + K
A photon with energy 28 eV strikes a metal surface If the kinetic energy of the ejected photoelectrons is 05 eV what is the work function of the metal
Wo = photon energy - K
Wo = 28 eV ndash 05 eV
Wo = 23 eV
hf = Wo + frac12 mv2
There is a minimum frequency called the ldquothreshold frequencyrdquo required to liberate an electron At the threshold frequency
Energy of photon = hfthreshold = Wo
That threshold photonrsquos wavelength is called the ldquocutoff wavelengthrdquo and can be found
using
c = f
Now you try some
If the cut-off wavelength for a particular metal is 320 nm what is the metalrsquos work function
First find the threshold frequency using c = f
Threshold frequency fo = 938 x 1014 Hz
Now find the work-function hfo = Wo
Be careful to use Planckrsquos constant with the correct units
h = 663 x 10-34Jmiddots or h = 414 x 10-15 eVmiddots
Wo = 622 x 10-19 J or Wo = 388 eV
What if a 450 nm light hit a surface with a work function of 236 eV What will be the kinetic energy of the photoelectron
First find the frequency of the 450 nm lightf = 667 x 1014 HzNow using conservation of energy
hf = Wo + Kinetic energySo K = hf ndash WoK = 040 eV How fast is the ejected electron movingK = frac12 mv2 m = 91 x 10-31 kg AND you have
to convert K back into Joules first
ExamplePhoton energy = Wo + K
A photon with energy 32 eV strikes a metal surface with a work function of 18 eV What is the kinetic energy of the ejected photoelectrons
K = photon energy ndash Wo
K = 32 eV ndash 18 eV
K = 14 eV
ExamplePhoton energy = Wo + K
A photon with energy 28 eV strikes a metal surface If the kinetic energy of the ejected photoelectrons is 05 eV what is the work function of the metal
Wo = photon energy - K
Wo = 28 eV ndash 05 eV
Wo = 23 eV
hf = Wo + frac12 mv2
There is a minimum frequency called the ldquothreshold frequencyrdquo required to liberate an electron At the threshold frequency
Energy of photon = hfthreshold = Wo
That threshold photonrsquos wavelength is called the ldquocutoff wavelengthrdquo and can be found
using
c = f
Now you try some
If the cut-off wavelength for a particular metal is 320 nm what is the metalrsquos work function
First find the threshold frequency using c = f
Threshold frequency fo = 938 x 1014 Hz
Now find the work-function hfo = Wo
Be careful to use Planckrsquos constant with the correct units
h = 663 x 10-34Jmiddots or h = 414 x 10-15 eVmiddots
Wo = 622 x 10-19 J or Wo = 388 eV
What if a 450 nm light hit a surface with a work function of 236 eV What will be the kinetic energy of the photoelectron
First find the frequency of the 450 nm lightf = 667 x 1014 HzNow using conservation of energy
hf = Wo + Kinetic energySo K = hf ndash WoK = 040 eV How fast is the ejected electron movingK = frac12 mv2 m = 91 x 10-31 kg AND you have
to convert K back into Joules first
ExamplePhoton energy = Wo + K
A photon with energy 28 eV strikes a metal surface If the kinetic energy of the ejected photoelectrons is 05 eV what is the work function of the metal
Wo = photon energy - K
Wo = 28 eV ndash 05 eV
Wo = 23 eV
hf = Wo + frac12 mv2
There is a minimum frequency called the ldquothreshold frequencyrdquo required to liberate an electron At the threshold frequency
Energy of photon = hfthreshold = Wo
That threshold photonrsquos wavelength is called the ldquocutoff wavelengthrdquo and can be found
using
c = f
Now you try some
If the cut-off wavelength for a particular metal is 320 nm what is the metalrsquos work function
First find the threshold frequency using c = f
Threshold frequency fo = 938 x 1014 Hz
Now find the work-function hfo = Wo
Be careful to use Planckrsquos constant with the correct units
h = 663 x 10-34Jmiddots or h = 414 x 10-15 eVmiddots
Wo = 622 x 10-19 J or Wo = 388 eV
What if a 450 nm light hit a surface with a work function of 236 eV What will be the kinetic energy of the photoelectron
First find the frequency of the 450 nm lightf = 667 x 1014 HzNow using conservation of energy
hf = Wo + Kinetic energySo K = hf ndash WoK = 040 eV How fast is the ejected electron movingK = frac12 mv2 m = 91 x 10-31 kg AND you have
to convert K back into Joules first
hf = Wo + frac12 mv2
There is a minimum frequency called the ldquothreshold frequencyrdquo required to liberate an electron At the threshold frequency
Energy of photon = hfthreshold = Wo
That threshold photonrsquos wavelength is called the ldquocutoff wavelengthrdquo and can be found
using
c = f
Now you try some
If the cut-off wavelength for a particular metal is 320 nm what is the metalrsquos work function
First find the threshold frequency using c = f
Threshold frequency fo = 938 x 1014 Hz
Now find the work-function hfo = Wo
Be careful to use Planckrsquos constant with the correct units
h = 663 x 10-34Jmiddots or h = 414 x 10-15 eVmiddots
Wo = 622 x 10-19 J or Wo = 388 eV
What if a 450 nm light hit a surface with a work function of 236 eV What will be the kinetic energy of the photoelectron
First find the frequency of the 450 nm lightf = 667 x 1014 HzNow using conservation of energy
hf = Wo + Kinetic energySo K = hf ndash WoK = 040 eV How fast is the ejected electron movingK = frac12 mv2 m = 91 x 10-31 kg AND you have
to convert K back into Joules first
Now you try some
If the cut-off wavelength for a particular metal is 320 nm what is the metalrsquos work function
First find the threshold frequency using c = f
Threshold frequency fo = 938 x 1014 Hz
Now find the work-function hfo = Wo
Be careful to use Planckrsquos constant with the correct units
h = 663 x 10-34Jmiddots or h = 414 x 10-15 eVmiddots
Wo = 622 x 10-19 J or Wo = 388 eV
What if a 450 nm light hit a surface with a work function of 236 eV What will be the kinetic energy of the photoelectron
First find the frequency of the 450 nm lightf = 667 x 1014 HzNow using conservation of energy
hf = Wo + Kinetic energySo K = hf ndash WoK = 040 eV How fast is the ejected electron movingK = frac12 mv2 m = 91 x 10-31 kg AND you have
to convert K back into Joules first
What if a 450 nm light hit a surface with a work function of 236 eV What will be the kinetic energy of the photoelectron
First find the frequency of the 450 nm lightf = 667 x 1014 HzNow using conservation of energy
hf = Wo + Kinetic energySo K = hf ndash WoK = 040 eV How fast is the ejected electron movingK = frac12 mv2 m = 91 x 10-31 kg AND you have
to convert K back into Joules first
