photoelectric effect = release of electrons from metal by light classical theory can explain it by...
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Photoelectric effect = Release of electrons from metal by light
• Classical theory can explain it by the force on the electrons by the oscillating electric and magnetic field in
light • But it cannot explain
1. for a given metal, the frequency of light wave must be greater than a threshold value
2. electrons are promptly emitted even with very low intensity light
3. the maximum kinetic energy of the electrons does not depend on the intensity of light
Photoelectric Effect
W
K
Kmax
hf
Bound electrons
Free electrons
W=work function of metal
K=kinetic energy of photoelectron
hf=W+Kmax
hfthreshold =W
photoelectric effect
The miracle year 1905
• During this year, Einstein was a clerk in a Swiss pattern office. He published papers on
• 1. the photoelectric effect
• 2. special theory of relativity
• 3. Brownian motion
Garage Door Opener
Charge Couple Device
Photovoltaic cell
Wave Particle Duality
double slit experiment simulation
Matter Wave (de Broglie)
p
h
mp 2
2
1c
mp
50g Tennis ball at 20m/s , λ=6.63×10-34mWave nature cannot be detected
Electron of kinetic energy 50eV, λ=3.9×10-10 mCan be detected sending electron beam through crystal
Examples
The uncertainty principle (Heisenberg) • In classical physics,
determination of a particle’s orbit requires knowing precisely its initial position and momentum (Δx=0;Δpx=0)
• In nature, this knowledge can never be obtained because
ΔxΔpx~h ΔyΔpy~h ΔzΔpz~h
The Uncertainty Principle Illustrated
y
x
y
p
p
x
y
p
p
y
Δyθ θ
hpp
hpyp x
xxy
yp
xp
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