Physics 121 Sample Common Exam 2 Rev2
NOTE: ANSWERS ARE ON PAGE 7
Name (Print): _______________________________
4 Digit ID:________ Section: ______
Instructions:
Answer all 27 multiple choice questions. You may need to do some calculation. Answer each question on the
Scantron sheet using #2 pencil. You may use backs of the question papers for extra space.
There are more problems in this sam[ple test than you would find on a real exam
1. A charge Q is placed on an isolated, hollow metal rectangular solid with closed ends as shown. How will this charge
be distributed after a while?
Q
A) The charge will be distributed uniformly over the volume of the solid.
B) The charge will continuously move along the surface, creating a constant current.
C) The charge will be concentrated as a point charge at the center of the solid.
D) The charge will be distributed over the outer surface of the solid.
E) The charge will be distributed over the outer and inner surfaces of the solid.
2. A negative charge Q = - 18 nC is placed inside an electrically neutral spherical conducting shell with the inner radius a
and the outer radius b. What charges will be induced on the inner and outer surfaces of the shell?
A.
B.
C.
D.
E.
Inner
Inner
Inner
Inner
Inner
charge
charge
charge
charge
charge
=
=
=
=
=
0 nC. Outer charge = 0 nC
–18 nC. Outer charge = +18 nC
+18 nC. Outer charge = -18 nC
0 nC. Outer charge = +18 nC
–18 nC. Outer charge = 0 nC
Q
3. The same negative charge Q = -18nC is placed on the same conducting shell as in the problem above, but now an
extra negative charge of – 40 nC is placed on the inner surface of the conductor. Now what will the charges be on the
inner and outer surfaces of the shell after a short time has passed for rearrangement?
A)
B)
C)
D)
E)
Inner charge = 0 nC. Outer charge = -40 nC
Inner charge = –18 nC. Outer charge = +18 nC
Inner charge = +18 nC. Outer charge = -18 nC
Inner charge = +18 nC. Outer charge = - 58 nC
Inner charge = –18 nC. Outer charge = 40 nC
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4. A point charge of 2.0 nano-coulombs is at the center of an (unbroken) egg-shell. What is the total electric flux
through the surface of the shell?
8.85 x 10-12 N⋅m2/C
9x109 N⋅m2/C
A)
D)
B) 226 N⋅m2/C
C) 0 N⋅m2/C
E) Answer depends on the diameter of the egg.
5. An electron moves from point i to point f, in the direction of a
uniform electric field. During this displacement:
i
A)
B)
C)
D)
E)
the
the
the
the
the
field
field
field
field
field
does
does
does
does
does
f
positive work, the potential energy of the electron does not change
positive work, the potential energy of the electron increases
negative work, the potential energy of the electron increases
positive work, the potential energy of the electron decreases
negative work, the potential energy of the electron decreases
6. The figure shows the electric potential as a function of the
distance x. In which region would the magnitude of the
electric field be the largest?
A)
B)
C)
D)
E)
Region 1
Region 2
Region 3
Region 4
Region 5
7. Three identical point charges have the same charge equal to +Q= +2 µC. The fourth charge has -Q = - 2 µC. They
are located at the corners of the diamond as shown in the diagram. Each side has length a = 2 m, with a 600 angle
located as shown. What is the electric potential at point E, the center of the diamond shape? The potential at infinity is
defined as the zero reference level.
Q
A) Zero Volts
0
4
60
B) 1.04 x 10 Volts
a
a
4
C) 2.08 x 10 Volts
4
D) 3.6 x 10 Volts
4
Q
-Q
E
E) 5.68 x 10 Volts
.
a
a
Q
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8. Which of the following statements about equipotential surfaces is false:
A)
B)
C)
D)
E)
An equipotential surface can be an imaginary surface.
An equipotential surface can be a real, physical surface.
Adjacent points that have the same electric potential form an equipotential surface.
The electric field lines are tangent to the equipotential surface at the point where the field is measured.
When a charged particle moves from one point to another on the same equipotential surface, the net work done is
equal to zero.
9. An extremely large nonconducting sheet creates equipotential surfaces, which are planes. The potential difference
between every two planes that are 2 mm apart is 1000 volts. What is the surface charge density
A)
B)
C)
D)
E)
σ on the sheet?
4.43 µC/m2
8.85 µC/m2
17.70 µC/m2
4.43 nC/m2
17.70 nC/m2
10. Which of the following statements is false?
The electric field E inside a parallel plate capacitor is uniform and equals - ∆V/∆x.
The plates of a capacitor are equipotential surfaces.
The plates of a capacitor have equal and opposite charges Q = CV on them.
The capacitance measures how much charge must be on the plates to produce some particular potential difference
across them.
E) The capacitance C = Q/V depends on the potential difference between the plates.
A)
B)
C)
D)
11. When a capacitor is connected to a 6 volt battery, 24
capacitance of the capacitor?
6
A) .25x10 µF
B) +144 µF
C) -144 µF
D) -4.0 µF
E) +4.0 µF
µC of charge appears on its negative plate. What is the
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12. If the plate separation of an isolated parallel-plate capacitor is decreased to one third of its original value:
A)
B)
C)
D)
E)
the capacitance is tripled
the capacitance remains the same
the capacitance is one third of its former value
none of the above
all of the above
13. Four identical capacitors are connected in series. In a separate circuit, three more capacitors, all identical to those in
the first group, are connected in parallel. What is the ratio of the equivalent capacitance for the series combination to the
equivalent capacitance of the parallel combination?
A)
4
B) 12
C) 3/4
D) 1/12
E) 4/3
14. Each of the three identical capacitors in the sketch has capacitance C = 1000 µF. Initially they are uncharged. The
potential difference supplied by the battery is V = 240 Volts. When the switch is closed, how many Coulombs of charge
flow through the meter A until the capacitors are fully charged?
A)
B)
C)
D)
E)
0.16 Coulombs
0.24 Coulombs
0.40 Coulombs
0.48 Coulombs
0.64 Coulombs
C
+
C
C
A
15. A network of current-carrying conductors is set up as shown
in the diagram. How many coulombs of charge pass through
the ammeter in 1 minute?
A)
B)
C)
D)
E)
150
900
200
1200
250
10 A.
4 A.
5 A.
4 A.
A
i
8 A.
3 A.
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16. Two wires are made of the same material and have the same length but different radii. They are joined end-to-end
and a potential difference is maintained across the combination. Of the following, the quantity that is the same for both
wires is:
A) potential difference across each wire
B) current inside each wire
C) current density inside each wire
D) resistance of each wire
E) electric field inside each wire
17. A wire that will be used in making an electric heater is 3.0 m long and 2.25 mm2 in cross-sectional area. It carries a
current of 4.5 A when a 3.0 V potential difference is applied between its ends. Calculate the resistivity
the wire.
A)
B)
C)
D)
E)
5.0 x
5.0 x
1.1 x
0.67
2.0 x
-7
10
-5
10
-6
10
Ω*m
+6
10
ρ of the metal in
Ω*m
Ω*m
Ω*m
Ω*m
18. A wire with a length of 1.5 m and a radius of 0.15 m carries a current of 2.0 A. The current density is about:
A)
B)
C)
D)
E)
0.28 A/m2
0.49 A/m
0.89 A/m2
1.3 A/m
28 A/m2
19. Which of the following graphs depicts the current versus voltage relationship for a device that obeys Ohm's Law?
A)
i
B)
i
V
C)
i
V
D)
E)
i
V
i
V
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V
20. If a piece of wire is stretched by 3 times what happens to the resistance (assume that the volume remains
constant)?
A.
B.
C.
D.
E.
Increases 3 times
Increases 9 times
Decreases 3 times
Decreases 9 times
Does not change
21. A physics professor "improving" the wiring in his house wants to put in a new circuit operating at 120 Volts that can
handle up to 25 light bulbs of 60 watts in parallel, which would consume a total power of 1500 W. What is the minimum
capacity, in Amperes, that he should use in deciding which kind of wire and fuse to install?
A)
B)
C)
D)
E)
0.5 Amps.
2.0 Amps.
10 Amps
15 Amps.
960 Amps
22. How much power is expended in a 1.0 kΩ resistor when it is connected across a 120-V voltage source?
A) 0.12 kW
B) 14.4 W
C) 1.2 W
D) 0.0012 W
E) 0.144 W
23. Find the equivalent resistance of the circuit shown in the sketch below.
A) 4.0 Ω
B) 4.5 Ω
C) 6
 .0 Ω
D) 3.0 Ω E) 2.5 Ω
1Ω
Req
5Ω
1Ω
4Ω
2Ω
1Ω
2Ω
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24. In the sketch, all bulbs have equal resistances. The brightness of bulbs B and C added together, compared with the
brightness of bulb A, is
A)
B)
C)
D)
E)
four times as large
twice as large.
the same.
half as large.
impossible to tell
25. The Kirchoff loop rule tells us that
A)
B)
C)
D)
E)
The sum of the electric fields around a closed loop equals zero
The sum of the currents around a closed loop equals zero
The sum of the electric charges around a closed loop equals zero
The sum of the emf's and potential differences around a closed loop equals zero
The sum of the resistances around a closed loop equals zero
26. A current of 2 A is flowing from point a to point b.
The potential difference Vb – Va is
A) –14 V
B) -8 V
C) -2 V
D) +4 V
E) +14 V
+
a
4Ω
2A
2V
2Ω
+
b
6V
27. The figure shows a plastic rod of length L = 50 cm, total positive charge Q = 1 µC., and uniform charge density λ ,
lying on an x axis. With V = 0 at infinity, find the electric potential (in volts) at point P1 on the axis, at distance d = 25
cm. to the left of one end of the rod.
Select the closest answer.
A)
B)
C)
D)
E)
zero
1
20,000
2
10,000
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Answers to Physics 121 Sample Common Exam 2 Rev 2
1.
2.
3.
4.
5.
6.
7.
8.
D
Charge distributed over the outer surface of the solid
C
D
B
C
B
C
D
Inner charge = +18 nC. Outer charge = -18 nC
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
21.
22.
23.
24.
25.
B
E
E
A
D
A
D
B
A
E
C
B
D
B
E
D
D
26.
27.
B
C
Inner charge = +18 nC. Outer charge = - 58 nC
226
N.m2/C
the field does negative work, the PE increases
Region 2
2.08 x 104 Volts
The field lines are tangent to equipotentials surface
at the point where the field is measured.
8.85 µC/m2
The capacitance C = Q/V depends on ∆V between plates.
+4.0 µF
the capacitance is tripled
1/12
0.16 Coulombs
1200
current inside each wire
5.0 x 10 -7 Ω*m
28 A/m2
straight line, positive slope
increases 9 times
15 Amps
14.4 Watts
2.5 Ω
half as large
The sum of potential differences around a
closed loop equals zero
-8 V
20,000
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