Last updated: September 16, 2008
PHY 2054 Discussion – Fall ‘08
Practice Exam Problems (Chapter 16)
1.
A uniform electric field, with a magnitude of 600 N/C, is directed paralledlt ot the positive x-axis. If
the potential at x = 3.0 m is 1 000 V, what is the potential at x = 1.0 m? (Electric Potential)
V
2.
b. 1 600 V
c. 2 200 V
a. 400
d. 2 500 V
Four point charges are on the rim of a circle of radius 10 cm. The charges are (in μC) +0.50, +1.5,
-1.0, -0.50. If the electrical potential at the circle’s center due to the +0.5 charge alone is 4.5×104 V,
what is the total potential at the center due to the four charges combined? (Electric potential due to
Point Charges)
3.
a. 18×104 V
b. 4.5×104 V
c. zero
d. -4.5×104 V
Two point charges of values +3.4 and +6.6 μC, respectively, are separated by 0.20 m. What is the
potential energy of this 2-charge system? (Potential Energy due to Point Charges)
-0.75 J
4.
c. +1.0 J
a. +0.34 J
b.
d. -3.4 J
There is a hollow, conducting uncharged sphere with a negative charge inside the sphere. Consider
the electrical potential at the inner and outer surfaces of the sphere. Which of the following is true?
(Potential in a Conductor)
the outer surface is greater.
a. The potential on the inner surface is greater.
b. The potential on
c. The potentials on both surfaces are zero.
d. The potentials on
both surfaces are equal but not zero.
5.
An electron with velocity v = 1.0×106 m/s is sent between the plates of a capacitor where the electric
field is E = 500 V/m. If the distance the electron travels through the field is 1.0 cm, how far is it
deviated (Y) in its path when it emerges from the electric field? (Kinematics in a Uniform Field)
a. 2.2 mm
b. 4.4 mm
c. 2.2 cm
d. 4.4 cm
1 cm
Y
v
6.
A parallel-plate capacitor has a capacitance of 20 µF. What potential difference across the plates is
required to store 7.2  104 C on this capacitor? (Capacitance)
1.4×10-8 V
d. 68 V
a.
36 V
b. 2.2×10-2 V
c.
7.
If the distance between two isolated parallel plates that are oppositely charged is doubled, the
electric field between the plates is essentially unchanged. However the: (Parallel Plate Capacitor)
a. potential difference between the plates will double.
b. charge on each plate will double.
force on a charged particle halfway between the plates will get twice as small.
c.
d. force on a
charged particle halfway between the plates will get four times as small.
8.
Three capacitors of 1.0, 1.5, and 2.0 μF are connected in series. Find the combined capacitance.
a. 4.5 μF
(Capacitors in Series)
9.
b. 2.0 μF
c. 2.2 μF
d. 0.47 μF
Two capacitors with capacitances of 1.5 and 0.25 μF, respectively, are connected in parallel. The
system is connected to a 50-V battery. What charge accumulates on the 1.5-μF capacitor?
(Capacitors in Parallel)
a.
100 μC
b. 75 μC
c. 50 μC
d. 33 μC
10. If C = 36 μF, determine the equivalent capacitance of the combination shown. (Equivalent
Capacitance)
a. 36 μF
b. 32 μF
c. 28 μF
d. 24 μF
2C
C
C
2C
11. Using a 1-mF capacitor, a 2-mF capacitor, and a 3-mF capacitor, which of the following
capacitances cannot be made by a combination that use all three? (Combinations of Capacitors)
6 mF
b. 6/11 mF
c. 11/3 mF
a.
d. 5/11 mF
12. Two capacitors with capacitances of 1.0 μF and 0.50 μF, respectively, are connected in series. The
system is connected to a 100-V battery. What electrical potential energy is stored in the 1.0-μF
capacitor? (Energy Stored in Capacitors)
a. 0.065×10-3 J
b. 4.3×10-3 J
c. 0.80×10-3 J
d.
-4
5.6×10 J
13. Inserting a dielectric material between two charged parallel conducting plates, originally separated
by air and disconnected from a battery, will produce what effect on the capacitor? (Properties of
Dielectrics)
a. increase charge
b. increase voltage
c. increase capacitance
d. decrease
capacitance
14. A capacitor is made by taking two sheets of aluminum foil, each 0.022 mm thick and placing
between them a sheet of paper which comes from a ream of 500 sheets, the ream being 5.5 cm thick
with sheets measuring 216 mm by 279 mm (the usual 8½ by 11). What is the capacitance of the
capacitor made this way if the dielectric constant of the paper is 3.7? (Capacitors with Dielectrics)
a. 24 nF
Answers: 1-c
b. 48 nF
2-b
3-c
c. 18 nF
4-d
5-b
d. 1.3 nF
6-a
7-a
8-d
9-b
10-d
11-d
12-d
13-c
14-c