# 77777 H. Monkhorst PHYSICS DEPARTMENT PHY 2005

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Instructor(s): H. Monkhorst
PHYSICS DEPARTMENT
PHY 2005
Exam 1
Name (print, last first):
January 28, 2005
Signature:
On my honor, I have neither given nor received unauthorized aid on this examination.
YOUR TEST NUMBER IS THE 5-DIGIT NUMBER AT THE TOP OF EACH PAGE.
(2) Print your name on this sheet and sign it also.
(3) Do all scratch work anywhere on this exam that you like. Circle your answers on the test form. At the end of
the test, this exam printout is to be turned in. No credit will be given without both answer sheet and printout with
scratch work most questions demand.
(4) Blacken the circle of your intended answer completely, using a #2 pencil or blue or black ink. Do not
make any stray marks or some answers may be counted as incorrect.
(5) The answers are rounded off. Choose the closest to exact. There is no penalty for guessing.
(6) Hand in the answer sheet separately.
g = 9.8 m/s
2
e = 1.6 &times; 10
−19
Physical Constants:
C constant k in Coulomb’s Law: k = 8.988 &times; 109 N&middot;m2 /C2
1. Two point charges exert a repulsive force of 400 &times; 10−9 N on each other when they are 4.5 m apart. What force will
one exert on the other when they are 2.5 m apart (in N)?
(1) 1.3 &times; 10−6
(2) −5 &times; 10−8
(4) 5 &times; 10−8
(3) 0.0
(5) not enough information
2. The electric field in a certain region is 500 N/C, directed straight downward. A 4-g ball hangs from a thread in this
region. Find the tension in the thread if the charge on the ball is −7.5&micro;C (in N).
(1) 3.545 &times; 10−2
(2) −3.545 &times; 10−2
(3) 4.295 &times; 10−2
(4) 3.545
(5) 42.95
3. An electron with unknown kinetic energy is brought to rest as it falls through a potential difference of 50 V. What
was its kinetic energy? (in Joules)
(1) 8.0 &times; 10−18
(2) −8.0 &times; 10−18
(3) 5.0 &times; 1018
(4) 502.1
(5) 9.0 &times; 10−9
4. What is the equivalent capacitance of 3-&micro;F, 9-&micro;F and 10-&micro;F capacitors when they are connected in series (in &micro;F)?
(1) 1.84
(2) 22.0
(3) −55.2
(4) 2.0
(5) 270
5. The electric field between two parallel plates is 3 &times; 105 V/m. Consider equipotential planes between the plates. We
wish the potential difference between them to be 15 V. How far apart are these two equipotential planes (in cm)?
(1) 5 &times; 10−3
(2) 5 &times; 10−5
(3) 5 &times; 103
(4) not enough information
(5) I do not know
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6. Find the equivalent resistance in the figure between points a and
b (in Ohms).
7Ω
10Ω
5Ω
a
(1) 9.118
(2) 4.625
(3) 22.001
b
(4) 12.002
7. Find the magnitude and direction of currents I1 , I2 , I3 for the
circuit shown (in A). Note: with the indicated directions in
this figure, the current direction is given by its sign.
(5) 0.912
Ω
Ω
15
20
12 V
I1
(1) (−0.6, −0.8, 1.4)
(2) (0.6, −0.8, 1.4)
(3) (−0.6, 0.8, −0.2)
I2
I3
(4) (−0.6, 0.8, −1.5)
(5) (0.6, 0.8, 1.4)
8. A certain electric clothes drier uses 3000 W of power. What current does it draw from a 120 V line (in A)?
(1) 25
(2) 50
(3) not enough information
(4) 0.21
(5) 0.42
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