LIGHT BEHAVES LIKE
WAVE - DIFRACTION EXPERIMENT
and
PARTICLE – PHOTOELECTRIC
EFFECT
de Broglie
WHAT WE CONSIDER PARTICLES
CAN BEHAVE LIKE BOTH ALSO.
CAN A PARTICLE (ELECTRON)
BEHAVE LIKE WAVE?
1
de Broglie
YES
WITH WAVELENGTH GIVEN BY
h
λ=
P
P = momentum= mv
2
DAVISSON GERMER EXPERIMENT
ELECTRONS WITH KNOW ENERGY
ARE FIRED AT CRYSTAL TARGET.
3
MEASURE NUMBER OF
ELECTRONS AT DETECTOR AS
FUNCTION OF ANGLE FOR
DIFFERENT ENERGIES.
4
AT 500 LARGE NUMBER ARRIVE
AT DETECTOR.
WHY?
WAVES CAN INTERFER
CONSTRUCTIVELY!
BUT PARTICLES?
AT 54 eV MORE ELECTRONS.
5
IF de BROGLIE CORRECT WHAT
WILL BE WAVELENGTH FOR 54eV
ELECTRONS?
1 2
−19 J
)
KE = mv = (54eV )(1.6 x10
2
eV
SOLVE FOR v
2(54eV )(1.6 x10
v=
−19
J
)
eV
m
6
m
v = 4.36 x10
s
6
m
p = mv = (9.1x10 kg)(4.36x10 )
s
−31
p = 3.97 x10
− 24
6
m
kg
s
7
deBroglie
−34
6.63x10 Js
h
λ= =
P 3.97 x10−24 kg m
s
λ = 1.66 x10
−10
m
8
FOR “WAVES” REFLECTED OFF
LATTICE
nλ = d sin Θ
WHERE d SPACING BETWEEN
LATTICE SITES
and
n IS THE NUMBER OF THE PEAK
9
nλ = d sin Θ
USE
n =1
λ = 1.66 x10
d = 2.15 x10
−10
−10
m
m
WHICH IS THE SPACING FOR
NICKEL
10
(1)(1.66 x10−10 m) = (2.15x10−10 m) sin Θ
(1.66 x10 −10 m)
sin Θ =
= 0.77
−10
(2.15 x10 m)
THUS
Θ = 50
0
11