AP Physics Chp 29

Wave-Particle Theory (Duality) Interference patterns by electrons

Blackbody E=nhf n=0,1,2,…. Quantized h= x Js

Photons E=hf “packet” of energy Photoelectric Effect

The minimum amount of energy needed to remove an electron from a metal surface by “light” is the work function W o hf = KE max + W o

Photons only have KE and no rest mass Use of photoelectric effect Dig Cameras and Safety Devices

Momentum of photons? Compton Effect X-ray scatters electrons and reflects itself

hf incident photon = hf’ photon + KE electron Momentum of photon p= h/λ Wavelenth Shift λ’ – λ = (h/mc) ( 1-cosθ) λ’ is the scattered photon

The work function for Gold is 3.9 eV ( 1ev=1.6x J ) What is the minimum frequency of “light” that will eject an electron?

Wo = 3.9eV x 1.6x J/eV =6.24x J hf = KE + Wo KE = 0 for the minumum hf = Wo f = Wo / h = 6.24x J / x Js f = 9.4x /s

de Broglie Wavelength λ= h/p λ= h/mv

Heisenberg Uncertainty Principle (∆p)(∆y) ≥ h/(4π) (∆E)(∆t) ≥ h/(4π)

What is the wavelength of a baseball (0.145 Kg) thrown at 44.7 m/s? What about an electron traveling 0.8c?

λ= h/mv = 6.626x Js / (0.145Kg)(44.7m/s) = 1.02x m

λ= h/mv = 6.626x Js / (9.11x Kg)(0.8c) = 3.05x m