Explanation by photon theory The result cant be explained by classical theory An electron is ejected from the metal by a collision (inelastic)with a single photon photon electron(be absorbed energy Minimum energy to get out: work function Wo hf=e +w k max Photoelectric equation
Explanation by photon theory 11 The result can’t be explained by classical theory An electron is ejected from the metal by a collision (inelastic) with a single photon. photon energy electron (be absorbed) Minimum energy to get out: work function W0 k max 0 hf E W Photoelectric equation
Compare with experiment E k max High intensity / Low intensity 1) Intensity of light keep! m, f doesnt change 2)E k max near relationship 3)f<f
Compare with experiment 12 k max 0 hf E W 1) Intensity of light ↗ n ↗ , f doesn’t change 2) Ek max 0 hf W linear relationship 3) 0 0 ? W f f h
Energy of photon Example3: The threshold wavelength for a metal surface is 350 nm. What is the ekmax when the wavelength changes to(a)280 nm,(b )380 nm? Solution: hf=E k max tn 0 10=hc/0 hc hc E k max (a)x=280m, EK=1.4×10J=0.89e (b)n=380nm>350nm No ejected electrons 13
Energy of photon 13 Example3: The threshold wavelength for a metal surface is 350 nm. What is the Ekmax when the wavelength changes to (a) 280 nm, (b) 380 nm? Solution: max 0 , h k f E W max 0 k hc hc E 19 max 1.4 10 Ek J (a) 280nm, W0 0 0 hf h c (b) 380nm 350nm No ejected electrons! 0.89eV
Compton effect Comptons x-ray scattering experiment(Nobel 1927) Scattering: light Lead shelter detector Monochromatic propagate in 0 □9 Graphite target different direction X-ray source EM waves: forced vibration> f(n=no) 八,A∵A
Compton effect 14 Compton’s x-ray scattering experiment (Nobel 1927) Scattering: light propagate in different direction EM waves: forced vibration → same f (=0)