Announcements
• Reading for Friday: 6.5 – 6.7
• No written HW due this Friday
Today’s class:
Electron interference!
Last Friday we found that if the
electron were a little wave going
around the nucleus its angular
momentum ‘L’ would be
quantized:
L = n
ħ
1
2
3
4
5
6
7
8
9
10
Case shown for n = 10
Can we just repeat light double slit experiment
with electrons?
A. Yes. (If so, what experimental results would
If electrons really are waves, we
should be able to see interference!
Q1
you expect?)
B. No. (If so, why not?)
Interference
Peaks align: ‘Constructive interference’
Interference
Peaks don’t align: ‘Destructive interference’
Doubleslit experiment
Determining the space between bright regions (H)
0.5 mm =D
r
1
r
2
θ
H
L
bright
bright
∆
r = r
2
r
1
Screen far away so
θ
1
~
θ
2
~
θ
& small angle approx. sin
θ
≈
θ
∆
r = D·sin(
θ
)
≈
D
θ
= m
λ
θ
1
θ
D
θ
2
H = L·sin(
θ
)
≈
L
θ
H=mL
λ
D
bright
∆
r = m
λ
(where m=1,2,3…)
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Doubleslit experiment
Determining the space between bright regions (H)
5 x10
4
m = D
r
1
r
2
∆
r = r
2
r
1
θ
H
L
∆
r = m
λ
(where m=1,2,3…)
∆
r=m
λ
= Dsin(
θ
)=
D
θ
=m
λ
H= L
θ
m = 1,
λ
= 500 nm, so angle to first bright portion:
θ
=
λ
/D = 500 x 10
9
/(5 x 10
4
) = 0.001 rad
if L = 3m, then H= 3 m x 0.001 = 3mm.
Calculating pattern for light
So what will pattern look like with electrons?
How figure out?
2. plug into
θ
=
λ
/D = (hc/pc)(1/D), calculate angle (radians)
Steps to predict pattern for debroglie electron wave.
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 Spring '08
 staff
 Physics, Electron, Angular Momentum, Momentum, Photon, Electrons, Wavelength, debroglie electron wave

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