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Physics 112
Exam I
Summer 2012
Name_________________
Physics 112
Summer 2012
Exam 1
Monday, Jun 25
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, place all exam materials, including the bubble
sheet, the exam itself, and scratch paper that you used for the exam, in your folder and
return the folder.
Good luck!
Page 1 of 7
Physics 112
Exam I
Summer 2012
1. Two charged spheres are 8.45 cm apart. They are moved, and the force on each of
them is found to have been tripled. How far apart are they now?
A) 2.88 cm
B) 3.88 cm
C) 4.88 cm
D) 5.88 cm
E) 6.88 cm
2. A charge of 6.00 mC is placed at each corner of a square 0.100 m
on a side. Determine the magnitude of the force on each charge.
A) 6.2x107 N
B) 3.2x107 N
C) 2.1x107 N
D) 1.0x107 N
E) 0.5x107 N
F42
F43
Q1
Q4
F41
d
Q3
Q2
3. If a solid metal sphere and a hollow metal sphere of equal diameters are each given
the same charge, the electric field (E) midway between the center and the surface is
A) Greater for the solid sphere than for the hollow sphere.
B) Greater for the hollow sphere than for the solid sphere.
C) Zero for both.
D) Nonzero, equal in magnitude for both.
E) Equal in magnitude for both, but one is opposite in direction from the other.
4. A styrofoam ball of mass 0.120 g is placed in an electric field of 6000 N/C pointing
downward. What charge must be placed on the ball for it to be suspended?
A) -16.0 nC
B) -57.2 nC
C) -125 nC
D) -196 nC
E) +16.0 nC
Page 2 of 7
Physics 112
Exam I
Summer 2012
5. Is it possible to have a zero electric field value between a negative and positive
charge along the line joining the two charges?
A) Yes, if the two charges are equal in magnitude.
B) Yes, regardless of the magnitude of the two charges.
C) No, a zero electric field cannot exist between these two charges.
D) Cannot be determined without knowing the separation between the two charges
E) Cannot be determined without knowing the magnitude of the two charges
6. A small charged ball is accelerated from rest to a speed v by a 500 V potential
difference. If the potential difference is changed to 2000 V, what will the new speed
of the ball be?
A) v
B) 2v
C) 4v
D) 16v
E) 24v
7. A negative charge is moved from point A to point B along an equipotential surface.
A) The negative charge performs work in moving from point A to point B.
B) Work is required to move the negative charge from point A to point B.
C) Work is both required and performed in moving the negative charge from point A to
point B.
D) Work is required if the equipotential surface is a sphere.
E) No work is required to move the negative charge from point A to point B.
8. A parallel-plate capacitor has a capacitance of C. If the area of the plates is doubled
and the distance between the plates is halved, what is the new capacitance?
A) C/4
B) C/2
C) C
D) 2C
E) 4C
Page 3 of 7
Physics 112
Exam I
Summer 2012
9. A battery charges a parallel-plate capacitor fully and then is removed. The plates are
immediately pulled apart. (With the battery disconnected, the amount of charge on
the plates remains constant.) What happens to the potential difference between the
plates as they are being separated?
A) It increases.
B) It decreases.
C) It remains constant.
D) It is zero.
E) Cannot be determined from the information given
10. Three identical capacitors are connected in parallel to a battery. If a total charge of Q
flows from the battery, how much charge does each capacitor carry?
A) 9Q
B) 3Q
C) Q
D) Q/3
E) Q/9
11. Two parallel plates, separated by 0.20 m, are connected to a 12-V battery. An
electron released from rest at a location 0.10 m from the negative plate. When the
electron arrives at a distance 0.050 m from the positive plate, what is the speed of the
electron?
A) 5.0 × 105 m/s
B) 1.0 × 106 m/s
C) 5.0 × 106 m/s
D) 1.0 × 107 m/s
E) Zero
12. The length of a wire is doubled and the radius is doubled. By what factor does the
resistance change?
A) Four times as large
B) Twice as large
C) Half as large
D) Quarter as large
E) The same
Page 4 of 7
Physics 112
Exam I
Summer 2012
13. A 1.0-mm diameter copper wire (resistivity 1.68×10-8 Ω∙m) carries a current of 15A.
What is the potential difference between two points 100 m apart?
A) 12 V
B) 23 V
C) 32 V
D) 41 V
E) 48 V
14. What is the nominal resistance of a 100-W light bulb designed to be used in a 120-V
circuit?
A) 1.2 Ω
B) 6 Ω
C) 12 Ω
D) 83 Ω
E) 144 Ω
15. A 500-W device is connected to a 120-V ac power source. What peak current flows
through this device?
A) 4.2 A
B) 5.9 A
C) 20 A
D) 120 A
E) 170 A
16. You obtain a 100-W light bulb and a 50-W light bulb. Instead of connecting them in
the normal way, you devise a circuit that places them in series across normal
household voltage. Which statement is correct?
A) Both bulbs glow at the same reduced brightness.
B) Both bulbs glow at the same increased brightness.
C) Both bulbs glow at the same brightness.
D) The 100-W bulb glows brighter than the 50-W bulb.
E) The 50-W bulb glows more brightly than the 100-W bulb.
17. A 22-A current flows into a parallel combination of a 4.0-Ω, 6.0-Ω, and 12-Ω
resistor. What current flows through the 4.0-Ω resistor?
A) 18 A
B) 11 A
C) 7.3 A
D) 3.7 A
E) 2.3 A
Page 5 of 7
Physics 112
Exam I
Summer 2012
18. What is the total resistance of the circuit in Fig.?
A) 80 Ω
B) 55 Ω
C) 50 Ω
D) 35 Ω
E) 20 Ω
19. 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
20. A 2.0-μF capacitor is charged through a 50-kΩ resistor. How long does it take for the
capacitor to reach 90% of full charge?
A) 0.90 s
B) 0.23 s
C) 2.2 s
D) 2.3 s
E) 1.2 s
Page 6 of 7
Physics 112
Exam I
Summer 2012
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
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