Physics 112
Exam I
Summer 2013
Name_________________
Physics 112
Summer 2013
Exam 1
Monday, July 1
Directions:
This 60-minute exam consists of twenty multiple-choice questions. This test is worth
20% of your final grade. (One point is equal to 1% of the final grade.)
The questions on this test are not in order of difficulty.
You must mark all of your answers on both your test and answer sheet.
In marking the multiple choice bubble sheet use a number 2 pencil. Do not use ink. If
you did not bring a pencil, ask for one. Fill in the appropriate circles completely. If you
need to change any entry, you must completely erase your previous entry.
Carefully read each question and its five possible answers. Select one and only one
answer for each question. Choose the answer that is closest to the correct one.
When you are finished with the exam, return the bubble sheet, the exam itself, and
scratch paper that you used for the exam.
Good luck!
Page 1 of 7
Physics 112
Exam I
Summer 2013
1. Two charged particles exert force F on each other. What will be the force if the
distance between the particles is doubled?
A) 4F
B) 2F
C) F
D) F/2
E) F/4
2. A  4.70 C and a  3.50 C charge are placed 18.5 cm apart. Where can a third
charge be placed so that it experiences no net force?
4.7 C
A) 116 cm to the right of the negative charge
B) 58 cm to the left of the negative charge
C) 8 cm to the right of the negative charge
D) 116 cm to the right of the positive charge
E) 58 cm to the right of the positive charge
+
–3.5 C
d
–
3. Three positive particles of equal charge, 11.0 C, are located at the corners of an
equilateral triangle of side 15.0 cm. Calculate the magnitude of electric field at the
center of the triangle.
A) 83.7 N/C
B) 7.6 N/C
C) 3.8 N/C
D) 0.69 N/C
E) 0
4. Calculate the magnitude of electric field at one corner of a square 1.00 m on a side if
the other three corners are occupied by 2.25 10 6 C charges.
A) 1.8  10 4 N / C
B) 3.9  10 4 N / C
C) 7.8  10 4 N / C
D) 4.5  10 5 N / C
E) 6.5  10 5 N / C
Page 2 of 7
Physics 112
Exam I
Summer 2013
5. The field just outside a 3.50-cm-radius metal ball is 2.75102 N C and points toward
the ball. What the field at 3.0 cm from the center of the ball?
A) 2.75102 N C and points toward the center
B) 2.75102 N C and points from the center
C) 1.98  10 2 N C and points toward the center
D) 1.98  10 2 N C and points from the center
E) 0
6. What is the net flux through the cube of side 10 cm if an electric charge of  2.0 C
is placed at 20 cm from the center of the cube?
A)  2.3  1011 Vm
B)  2.3  1011 Vm
C)  4.6  1011 Vm
D)  4.6  1011 Vm
E) 0
7. Two point charges are arranged at the corners of an equilateral triangle of side L.
What is the potential at the third corner, taking V  0 ?
Q
A) V  k
L
Q
B) V  2k
L
Q
C) V  k 2
L
Q
D) V  2k 2
L
E) 0
8. How strong is the electric field between the plates of a 0.80-F air-gap capacitor if
they are 2.0 mm apart and each has a charge of 72 C?
A) 2.5  10 4 V / m
B) 3.0  10 4 V / m
C) 3.5  10 4 V / m
D) 4.5  10 4 V / m
E) 5.0  10 4 V / m
Page 3 of 7
Physics 112
Exam I
Summer 2013
9. How much energy is stored by the electric field between two square plates, 8.0 cm on
a side, separated by a 1.5-mm air gap? The charges on the plates have opposite signs
and are of equal magnitude 420 C.
A) 1.3  10 5 J
B) 7.8  10 4 J
C) 2.3  10 3 J
D) 4.6  10 2 J
E) 1.2  10 2 J
10. Capacitances of 10 μF and 20 μF are connected in parallel, and this pair is then
connected in series with a 30-μF capacitor. What is the equivalent capacitance of this
arrangement?
A) 10 μF
B) 15 μF
C) 25 μF
D) 60 μF
E) 66 μF
11. An electron starts from rest 32.5 cm from a fixed point charge with Q  0.125 C.
How fast will the electron be moving when it is very far away?
A) 4.6  10 5 m / s
B) 8.3  10 6 m / s
C) 3.5  10 7 m / s
D) 2.3  10 8 m / s
E) 1.2  10 9 m / s
12. Determine the voltage across 680 resistor.
A) 5.3 V
B) 7.2 V
C) 9.0 V
D) 12 V
E) 0
Page 4 of 7
Physics 112
Exam I
Summer 2013
13. A 120-V hair dryer has two settings: 850 W and 1250 W. At which setting do you
expect the resistance to be higher?
A) 850 W
B) 1250 W
C) 850 W for small current, and 1250 W big current
D) 1250 W for small current, and 850 W big current
E) The same
14. Eight 7.0-W Christmas tree lights are connected in series to each other and to a 110-V
source. What is the resistance of each bulb?
A) 432
B) 216
C) 108
D) 54
E) 27
15. Calculate the terminal voltage for a battery with an internal resistance of 1.0  and
an emf of 9.0 V when the battery is connected in series with a 14.0- resistor.
A) 9.0V
B) 8.8 V
C) 8.4 V
D) 8.0 V
E) 7.8 V
16. Calculate the peak current in a 2.2-k resistor connected to a 220-V rms ac source.
A) 140 A
B) 100 A
C) 10 A
D) 0.14 A
E) 0.10 A
Page 5 of 7
Physics 112
Exam I
Summer 2013
17. Kirchhoff's junction rule is an example of
A) conservation of energy
B) conservation of charge
C) conservation of linear momentum
D) conservation of angular momentum
E) none of the given answers
18. Which of the equations here is valid for the circuit shown? (Current I is in amperes)
A) 2 - I1 - 2I2 = 0
B) 2 - 2I2 - 4I3 = 0
C) 4 - I1 + 4I3 = 0
D) 2 - I1 - 2I3 = 0
E) 6 - I1 - 2I2 = 0
19. The relaxation time of the RC circuit is  . The initial current is 10 mA.
What current will be after 3 seconds?
A) 3.7 mA
B) 3.0 mA
C) 2.5 mA
D) 1.8 mA
E) 0.5 mA
20. A 4.0-MΩ resistor is connected in series with a 0.50-μF capacitor. The capacitor is
initially uncharged. The RC combination is charged by a 9.0-V battery. What is the
change in voltage between t = RC and t = 3RC?
A) 11 V
B) 7.6 V
C) 5.7 V
D) 2.9 V
E) 1.3 V
Page 6 of 7
Physics 112
Exam I
Summer 2013
Record Sheet
You may fill in this sheet with your choices, detach it and take it with you after the exam
for comparison with the posted answers
1
11
2
12
3
13
4
14
5
15
6
16
7
17
8
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9
19
10
20
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