Quantization of Light Chapter 4

Chapter 4 Homework 4.9, 4.15, 4.23, 4.31 Due Monday 2/24

This week Lecture today Problems, questions Wednesday Quiz and makeup quizzes Friday –Makeups if you qualify –(Do the relevant HW by Wednesday)

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

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”

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

Photoelectric Effect Explained by Einstein E = hf –  Verified by Millikan slope = h E f –– 0

Photoelectric Effect Work function  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

X rays “Braking radiation” from stopped electrons Electromagnetic radiation hf max = K e = Ve – + V X

X rays are Light Uncharged Diffract from crystals

Compton Effect X-rays lose energy scattering from electrons Interpreted as elastic scattering conserving momentum hf 1 hf 2

Photon Momentum E 2 = (mc 2 ) 2 + (pc) 2 (hf) 2 = (pc) 2 hf = pc p = hf/c p = h(c/ )/c p = h/