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1
Physics 316
Solution for quiz 1
Spring 2005
Cornell University
Steve Drasco
I.
EXERCISE 1
We know from Wein’s displacement law that
ν
max
∝
T
. Therefore
T
→
T/
3 means that
ν
max
→
ν
max
/
3 = 117
THz. We know from Stefan’s law that
P
∝
T
4
. Therefore
T
→
T/
3 means that
P
→
P/
81 = 12
.
3 W.
II.
EXERCISE 2
We will use conservation of energy. The total initial energy is only the kinetic energy of the electron
E
i
=
K
e
.
The total Fnal energy is that of the photon plus the potential energy of the now bound electron
E
f
=
hν
max

W
.
Equating
E
i
and
E
f
gives
ν
max
= (
K
e
+
W
)
/h
.
III.
EXERCISE 3
A photon emitted after a change from level
n
i
to
n
f
has energy
hν
∝
n

2
f

n

2
i
. ±or the Frst Balmer line
n
f
= 2
and
n
i
= 3. ±or the Frst Lyman line
n
f
= 1 and
n
i
= 2. So if the frequency of the Frst Lyman line is
ν
L
then
hν
L
hν
B
=
1

1
/
4
1
/
4

1
/
9
=
3
/
4
9
/
36

4
/
36
=
3
4
36
5
=
27
5
,
(3.1)
which means that
ν
L
= (27
/
5)
ν
B
= 2470 THz.
IV.
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This note was uploaded on 09/28/2008 for the course PHYS 316 taught by Professor Hoffstaetter during the Spring '05 term at Cornell University (Engineering School).
 Spring '05
 HOFFSTAETTER
 Physics

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