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Homework 14 solutions
Physics 204, morning summer 2008
Chapter 29
Problems 8,21,38,43
Chapter 30
Problems 18,15
8.
REASONING AND SOLUTION
The work function of the material (using
λ
= 196 nm) is found from
W
0
=
hf
=
hc
/
= 1.01
×
10
–18
J
The maximum kinetic energy of the ejected electron is (using
= 141 nm)
KE
max
=
hf
−
W
0
=
hc
/
−
W
0
= 3.96
×
10
–19
J
The speed of the electron is then
v
m
==
×
×
=×
−
−
2
2 3 96
10
932 10
19
5
KE
J
9.11 10
kg
m/s
max
31
ch
.
.
21.
REASONING AND SOLUTION
The de Broglie wavelength
is given by Equation 29.8 as
=
h
/
p
,
where
p
is the magnitude of the momentum of the particle.
The magnitude of the momentum is
p
=
mv
,
where
m
is the mass and
v
is the speed of the particle.
Using this expression in Equation 29.8, we find that
=
×⋅
××
h
mv
v
h
m
or
6.63
10
J s
1.67
10
kg
0.282
10
m
141 10 m s
–34
–27
–9
3
.
/
38.
REASONING
The energy of a photon of frequency
f
is, according to Equation 29.2,
Eh
f
=
, where
h
is
Planck's constant.
Since the frequency and wavelength are related by
fc
=
/
(see Equation 16.1), the
energy of a photon can be written in terms of the wavelength as
c
=
/
.
These expressions can be
solved for both the wavelength and the frequency.
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 Spring '09
 rollino
 Physics

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