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PHYS1200
PHYSICS II
SPRING 2005
HOMEWORK SOLUTIONS
CLASS 22.
38.10, 38.19, 38.28, 38.68; Q38.09, Q38.13
38.10.
a)
The rate of solar energy (or solar power) that strikes the panel is,
P = IA =
(1.39 kW/m²)(2.60 m²)
P
= 3.61 kW
b)
The rate at which solar photons are absorbed by the panel is,
m/s)
10
s)(3.0
J
10
(6.63
m)
10
W)(550
10
61
.
3
(
8
34
9
3
×
⋅
×
×
×
=
=
=
=


hc
P
hf
P
E
P
R
photon
λ
R
= 9.98 ×10
21
s
1
c)
Avogadro’s number is the number of photons in one mole, so the time to collect one
mole of photons is,
1

21
23
s
10
98
.
9
10
02
.
6
×
×
=
=
R
N
t
A
t
= 60.3 s
38.19.
a)
K
max
= hf
–
φ
=
eV
20
.
4
m
10
00
2
m/s)
10
s)(3.0
eV
10
(4.14
9
8
15

×
×
⋅
×
=



hc
K
max
=
2.01 eV
b)
The least energetic electron that escapes has just enough energy to get out, so it has no
kinetic energy.
K
min
=
0
c)
The stopping potential is given by,
eV = K
max
. So,
C
10
1.6
J/eV)
10
eV)(1.6
01
.
2
(
19
19
max


×
×
=
=
e
K
V
V
= 2.01 V
d)
The cutoff wavelength is given by,
=
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 Spring '06
 Stoler
 Energy, Power, Work, Photon

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