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Electromagnetic Energy
Waves… a reviewMost waves are either
longitudinal or transverse.Sound waves are longitudinal.But all electromagnetic waves
are transverse…
?
?
Electromagnetic waves Produced by the movement of
electrically charged particles Can travel in a “vacuum” (they do
NOT need a medium Travel at the speed of
light Also known as EM waves
Wave-particle Duality Light can behave like a wave or like a
particle A “particle” of light is called a photon
Radio waves Longest wavelength EM waves Uses:
TV broadcasting AM and FM broadcast radio Avalanche beacons Heart rate monitors Cell phone communication
Microwaves Wavelengths from 1 mm- 1 m Uses:
Microwave ovens Bluetooth headsets Broadband Wireless Internet Radar GPS
Infrared Radiation Wavelengths in between microwaves
and visible light Uses:
Night vision goggles Remote controls Heat-seeking missiles
Visible light Only type of EM wave able to be
detected by the human eye Violet is the highest frequency light Red light is the lowest frequency
light
Ultraviolet Shorter wavelengths than visible
light Uses:
Black lights Sterilizing medical equipment Water disinfection Security images on money
Ultraviolet (cont.)UVA UVB and UVC
Energy Highest of UV waves
Lower than UVA
Health risks
Extremely low risk for DNA damage Can destroy Vitamin A in skin
Can cause DNA damage, leading to skin cancer Responsible for sunburn
X-rays Tiny wavelength, high
energy waves Uses:
Medical imaging Airport security Inspecting industrial welds
Gamma Rays Smallest wavelengths, highest
energy EM waves Uses
Food irradiation Cancer treatment Treating wood flooring
Calculations with Waves Frequency: number of wave peaks
that occur in a unit of time Measured in Hertz (Hz) Represented by nu (v)
Wavelength: the distance between wave peaks Represented by lambda (λ)
c= λv, c=3.0 x 108 m/s
Understanding Wavelength/Frequency
If the wavelength is longer, the frequency is low
If the wavelength is shorter, the frequency is high
Practice
A certain green light has a frequency of 6.26 x 1014 Hz.
What is its wavelength?
Max Planck Assumed energy was given off in little
packets, or quanta (quantum theory) He called these quanta photons. He determined the energy of this quanta of
light could be calculated
E=hvE: quantum of energy
h: constant, 6.626 x 10-34 J/Hzv: frequency of the wave
Practice
What is the energy content of one quantum of the light in the previous problem?
Bohr Model of Atom Proposes that the atom is
“quantized” As electrons move around the nucleus, they
have specific energies Only certain electron orbits (energy levels) are
allowable
Bohr Model Atoms are most stable when their
electrons are orbiting around the atom with the lowest possible energies. This lowest energy state is the ground state.
If the electrons absorb energy, the atom can leave the ground state and jump to a higher energy state called the excited state.
Bohr Model The electron jump (a quantum leap)
occurs when an atom absorbs a packet of electromagnetic energy called a photon.
Only photons of certain energies are absorbed during this process
Quantum Leaps Create a high energy state for the
atom which is not favored by nature and is unstable
Electrons immediately release the energy that they absorbed to return back to ground state
Energy Released The energy is released as specific
energies of visible light which we see as different colors
Types of Spectra Absorption (dark-line) spectra appear as a
rainbow of colors with dark lines in it. Each dark line represents a specific amount of energy that an electron absorbs as it quantum leaps into a higher energy orbit
Types of Spectra Emission (bright-line) spectra appear as a dark
background with lines of color in it. Each colored line represents a specific amount of energy that an electron releases as it quantum leaps back to its original orbit.
What do you notice?
Analyzing Spectra Analysis of the spectra of different
substances is the basis for spectroscopy The study of the energy which is given off and
absorbed when atoms go from the ground state to the excited state and back again
Image credits1. http://www.antonine-education.co.uk/New_items/MUS/images/M
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n12.jpg3. http://abyss.uoregon.edu/~js/glossary/wave_particle.html4. http://www.astro.princeton.edu/~gk/A402/electromagnetic_spec
trum.jpg5. http://science.hq.nasa.gov/kids/imagers/ems/radio.html6. http://www.nentjes.info/Palace/radio-6.gif7. http://www.mobilewhack.com/motorola-h12-bluetooth-headset.j
pg8. http://www.stuffintheair.com/radar-real-time-weather.html9. http://www.imaging1.com/gallery/images/AV%20Night%20vision
%20goggles.jpg10. http://www.global-b2b-network.com/direct/dbimage/50329753/S
tudy_Remote_Control.jpg11. http://www.georgiaprismaward.com/The_Prism_Story_files/PRIS
M%20brand%20imagemed.jpg12. http://science.hq.nasa.gov/kids/imagers/ems/uv.html
Image Credits13. http://farm3.static.flickr.com/2385/2381723771_12548f4b
d1.jpg?v=121742987914. http://intamod.com.au/images/uv2.JPG15. http://science.hq.nasa.gov/kids/imagers/ems/xrays.html16. http://www.sciencelearn.org.nz/var/sciencelearn/storage/
images/contexts/see_through_body/sci_media/neck_x_ray/17945-5-eng-NZ/neck_x_ray_full_size_portrait.jpg
17. http://www.epinion.eu/wordpress/wp-content/uploads/2008/05/airport-security1.jpg
18. http://science.hq.nasa.gov/kids/imagers/ems/gamma.html19. http://www.aboutnuclear.org/print.cgi?fC=Food20. http://www.roswellpark.org/files/1_2_1/brain_spinal/
gamma%20knife%204c.jpg
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