Modern Physics Chapters 38-40. Wave-Particle Duality of Light Young’s Double Slit Experiment...

Modern PhysicsChapters 38-40

Wave-Particle Duality of Light Young’s Double Slit Experiment (diffraction)

proves that light has wave properties So does Interference and Doppler Effect

Photoelectric Effect proves that light has properties of particles

Max Planck From Planck’s work on Blackbody Radiation, he

proposed that the energy of light is quantized

Quantization is an idea that energy comes in bundles or discrete amounts Energy is quantized

This idea disagreed with established (traditional) physics

Photoelectric Effect Light shining on a photo-sensitive metal plate

will emit electrons.

Photoelectric Effect

Photoelectric Effect Frequency must be above a minimum

(threshold) frequency

Brighter light (higher intensity) produces more electrons, but with the same energy

Light with higher frequency will emit electrons with higher energy

Photoelectric Effect Law of Conservation of Energy must be

followed Energy must be related to frequency

Law of Conservation of Momentum must also be followed Light has momentum

Photoelectric Effect Einstein used previous work by Max Planck

to explain Photoelectric Effect (Nobel Prize 1921)

Proposed that discrete bundles of light energy are photons

Energy is proportional to Frequency E=hf

h, Planck’s Constant 6.63 x 10-34 J*s

Equations

fc

hchfE

cf

Compton Effect 1923 Arthur Compton uses photon

model to explain scattering of X-rays

Determines equation for momentum of a photon

Compton Effect X-ray photon strikes an electron at rest

After the collision both the electron and X-ray photon recoil (move) in accordance with Laws of Conservation of Momentum and Energy

The photon transfers some momentum to the electron during collision.

Compton Effect Change in wavelength

of photon must be related to momentum

Magnitude of Photon Momentum:

h

chfmvp

de Broglie Wavelength 1923, graduate student, Louis de Broglie

suggested that if light waves could exhibit properties of particles, particles of matter should exhibit properties of waves

Used same equation as momentum of photon

mvh

ph

Standard Model Matter is classified into 2 types

Hadrons and Leptons

The Quark Family, also called Hadrons, are classified further into 2 types Baryons and Mesons

Quarks Six quarks

Up, Down, Top, Bottom, Strange, and Charm

Up, Charm, and Top all have +2/3e charge Down, Strange, and Bottom all have -1/3e charge

They all have different masses

Baryons Baryons are comprised (made of) three

quarks The total charge for any baryon is the net

charge of the three quarks together (-1, 0, +1, +2)

Examples: uud = +2/3, +2/3, -1/3 = +1 = proton udd = +2/3, -1/3, -1/3 = 0 = neutron

Mesons Mesons are comprised of a quark and its

antiquark

Antimatter Particles that have the same mass but opposite

charge of their matter partner Have same symbol as matter but with added bar

above symbol Up quark, u up antiquark, ū

Leptons Leptons are separated into six flavours

Electron, Muon, and Tau all have -1 charge Electron neutrino, muon neutrino, and tau

neutrino all have 0 charge

Annihilation When matter and antimatter particles collide,

they annihilate each other and produce energy

E=mc2

kg J (use equation) u eV (use conversion on Reference Tables)

Fundamental Forces Strong Force

Force that holds nucleons (protons and neutrons) together

Short range

Weak Force Associated with radioactive decay Short Range

Fundamental Forces Gravitational Force

Attractive only Long distance range (think planets)

Electromagnetic Force Attractive and repulsive force on charged particles Long range (think stars)

Mass Defect and Binding Energy Mass Defect

Difference between the actual mass of the atom and the sum of the individual masses of the protons, neutrons, and electrons.

Binding Energy The amount of energy that must be supplied to a

nucleus to completely separate its nuclear particles

Mass defect converted to energy, E=mc2

Mass-Energy Conversion E=mc2

Kg J u eV

1 u = 1.4924 x 10-10 J

1 u = 9.31 x 108 eV = 931 MeV