1
PHY108
Fall 2010
EXAM 2
October
23,
9:00 – 11:00 a.m.
Circle your instructor’s name
:
Prof. Ia Iashvili
(
T,Th 12:301:45 pm)
Prof. Athos Petrou
(
M,W,F 2:002:50 pm)
PRINT YOUR NAME
LAST NAME
FIRST NAME
SIGN YOUR NAME
STUDENT ID NUMBER
Useful Constants
o
= 8.85
10
12
C
2
/N.m
2
k
= 8.99
10
9
kg.m
3
.s
2
.C
2
e
= 1.60
10
19
C
m
p
= 1.67
10
27
kg
m
n
= 1.67
10
27
kg
m
e
= 9.11
10
31
kg
N
A
= 6.02
10
23
atoms/mol
INSTRUCTIONS
This is a closed book exam except that you are allowed one 8.5”x11” sheet with
whatever you wish to write on it.
There are 4 problems – you must attempt them all.
Allow approximately 20 minutes for each problem.
You must show ALL your work to receive full credit.
Numerical answers must have SI units and the appropriate number of
significant figures.
Use the back of the problem page if you need more space and mark OVER on
the front side to indicate that there is material at the back side.
Enter your answers in the box at the bottom of each page.
PROBLEM
NUMBER
MAXIMUM
SCORE
YOUR SCORE
GRADER
1
25
2
25
3
25
4
25
TOTAL
100
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P1.
Consider the square shown in the figure that has side length
a
=14.0 cm.
A charge
1
2.00
C
q
is placed at point (0 cm, 0 cm).
A charge
2
3.00
C
q
is placed at point
(14.0 cm, 0 cm).
A charge
3
5.00
C
q
is placed at point(0 cm, 14.0 cm).
a.
(7)
Calculate the electric potential
A
V
at point A (14.0 cm. 14.0 cm).
b.
(7)
Calculate the potential energy
U
of the three charges.
c.
(3)
Did an external agent have to do work to assemble the three charges or not?
Explain briefly.
d.
(5)
A charge
1.00
C
Q
is moved by an external agent from infinity to point A.
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 Fall '08
 IASHVILI
 Electrostatics, Energy, Electric charge, Permittivity, Wext

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