1. Quantization of Light
It seemed to be a wave...

2. Black-body Radiation
Does not preferentially absorb or emit any particular frequency
Light in thermal equilibrium with surroundings
Experimentally realized as “Cavity” radiation

3. Black-Body Spectrum
Classically, emission at short wavelengths would be infinite
Planck correctly modeled spectrum by assuming
E = hf
Sharp drop in high-f “photons”

4. Photoelectric Effect Light absorbed by a metal can eject electrons
Energy of photoelectrons did not depend on light intensity P/A (Instead, that determined the current)
Light frequency determined photoelectron energy

5. Photoelectric Effect Explained by Einstein E = hf – f
slope = h E f –f
Verified by Millikan

6. Photoelectric Effect Work function f of metal
property of the metal
potential energy of bound electron
light carries and delivers energy in hf packets (photons)
Light can act as discrete particles, not just continuous waves

7. X rays “Braking radiation” from stopped electrons
Electromagnetic radiation X
– + V
hfmax = Ke = Ve

8. X rays are Light
Uncharged
Diffract from crystals

9. Compton Effect X-rays lose energy scattering from electrons
hf1
hf2
X-rays lose energy scattering from electrons
Interpreted as elastic scattering conserving momentum

10. Photon Momentum
E2 = (mc2)2 + (pc)2 (hf)2 = (pc)2 hf = pc p = hf/c p = h(c/l)/c p = h/l