Chapter 26
Capacitance and Dielectrics
Multiple Choice
1.
Determine the equivalent capacitance of the combination shown when C = 12 pF.
C
C
C
2C
a.
b.
c.
d.
e.
2.
48 pF
12 pF
24 pF
6.0 pF
59 pF
Determine the equivalent capacitance of the combination shown when C = 15
mF.
C
C
a.
b.
c.
d.
e.
3.
2C
C
20 mF
16 mF
12 mF
24 mF
75 mF
Determine the equivalent capacitance of the combination shown when C = 12 nF.
a.
b.
c.
d.
e.
2C
C
C
3C
34 nF
17 nF
51 nF
68 nF
21 nF
75
76
4.
CHAPTER 26
Determine the equivalent capacitance of the combination shown when C = 45 μF.
C
2C
C
a.
b.
c.
d.
e.
5.
2C
36 μF
32 μF
34 μF
30 μF
38 μF
If C = 10 μF, what is the equivalent capacitance for the combination shown?
C
8.0 μF
a.
b.
c.
d.
e.
6.
6.0 μF
7.5 μF
6.5 μF
7.0 μF
5.8 μF
13 μF
What is the equivalent capacitance of the combination shown?
12 μF
24 μF
20 μF
12 μF
a.
b.
c.
d.
e.
29 μF
10 μF
40 μF
25 μF
6.0 μF
Capacitance and Dielectrics
7.
What is the equivalent capacitance of the combination shown?
a.
b.
c.
d.
e.
8.
77
20 μF
30 μF
10 μF
30 μF
20 μF
90 μF
22 μF
4.6 μF
67 μF
Determine the equivalent capacitance of the combination shown when C = 45 μF.
C
2C
3C
6C
a.
b.
c.
d.
e.
9.
28 μF
36 μF
52 μF
44 μF
23 μF
Determine the equivalent capacitance of the combination shown when C = 24 μF.
C
2C
2C
2C
2C
a.
b.
c.
d.
e.
20 μF
36 μF
16 μF
45 μF
27 μF
78
10.
CHAPTER 26
Determine the energy stored in C2 when C1 = 15 μF, C2 = 10 μF, C3 = 20 μF, and
V0 = 18 V.
C1
+
V0
C2
–
a.
b.
c.
d.
e.
11.
C3
0.72 mJ
0.32 mJ
0.50 mJ
0.18 mJ
1.60 mJ
Determine the energy stored in C1 when C1 = 10 μF, C2 = 12 μF, C3 = 15 μF, and
V0 = 70 V.
C1
C2
+
C3
–
V0
a.
b.
c.
d.
e.
12.
6.5 mJ
5.1 mJ
3.9 mJ
8.0 mJ
9.8 mJ
Determine the energy stored by C4 when C1 = 20 μF, C2 = 10 μF, C3 = 14 μF,
C4 = 30 μF, and V0 = 45 V.
C2
C3
C1
C4
+
–
V0
a.
b.
c.
d.
e.
3.8 mJ
2.7 mJ
3.2 mJ
2.2 mJ
8.1 mJ
Capacitance and Dielectrics
13.
Determine the charge stored by C1 when C1 = 20 μF, C2 = 10 μF,C3 = 30 μF, and
V0 = 18 V.
C2
C1
C3
+
–
V0
a.
b.
c.
d.
e.
14.
0.37 mC
0.24 mC
0.32 mC
0.40 mC
0.50 mC
What is the total energy stored by C3 when C1 = 50 μF, C2 = 30 μF, C3 = 36 μF,
C4 = 12 μF, and V0 = 30 V?
C1
C2
C3
+
C4
–
V0
a.
b.
c.
d.
e.
15.
6.3 mJ
25 mJ
57 mJ
1.6 mJ
14 mJ
How much energy is stored in the 50-μF capacitor when Va – Vb = 22V?
a
25 μF
50 μF
b
a.
b.
c.
d.
e.
25 μF
0.78 mJ
0.58 mJ
0.68 mJ
0.48 mJ
0.22 mJ
79
80
16.
CHAPTER 26
What is the total energy stored in the group of capacitors shown if the charge on
the 30-μF capacitor is 0.90 mC?
30 μF
20 μF
15 μF
a.
b.
c.
d.
e.
17.
29 mJ
61 mJ
21 mJ
66 mJ
32 mJ
What is the potential difference across C2 when C1 = 5.0 μF, C2 = 15 μF, C3 = 30 μF,
and V0 = 24 V?
C1
C2
C3
+
–
V0
a.
b.
c.
d.
e.
21 V
19 V
16 V
24 V
8.0 V
Capacitance and Dielectrics
18.
What total energy is stored in the group of capacitors shown if the potential
difference Vab is equal to 50 V?
50 μF
a
10 μF
b
20 μF
a.
b.
c.
d.
e.
19.
48 mJ
27 mJ
37 mJ
19 mJ
10 mJ
Determine the energy stored in the 60-μF capacitor.
25 μF
50 V
40 μF
a.
b.
c.
d.
e.
20.
60 μF
2.4 mJ
3.0 mJ
3.6 mJ
4.3 mJ
6.0 mJ
Determine the energy stored in the 40-μF capacitor.
25 μF
50 V
40 μF
a.
b.
c.
d.
e.
2.4 mJ
1.6 mJ
2.0 mJ
2.9 mJ
4.0 mJ
60 μF
81
82
21.
CHAPTER 26
If VA – VB = 50 V, how much energy is stored in the 36-μF capacitor?
36 μF
A
B
72 μF
54 μF
a.
b.
c.
d.
e.
22.
50 mJ
28 mJ
13 mJ
8.9 mJ
17 mJ
If VA – VB = 50 V, how much energy is stored in the 54-μF capacitor?
36 μF
A
B
72 μF
54 μF
a.
b.
c.
d.
e.
23.
A 3.0-μF capacitor charged to 40 V and a 5.0-μF capacitor charged to 18 V are
connected to each other, with the positive plate of each connected to the negative
plate of the other. What is the final charge on the 3.0-μF capacitor?
a.
b.
c.
d.
e.
24.
50 mJ
13 mJ
28 mJ
8.9 mJ
17 mJ
11 μC
15 μC
19 μC
26 μC
79 μC
A 6.0-μF capacitor charged to 50 V and a 4.0-μF capacitor charged to 34 V are
connected to each other, with the two positive plates connected and the two
negative plates connected. What is the total energy stored in the 6.0-μF capacitor
at equilibrium?
a.
b.
c.
d.
e.
6.1 mJ
5.7 mJ
6.6 mJ
7.0 mJ
3.8 mJ
Capacitance and Dielectrics
25.
A 25-μF capacitor charged to 50 V and a capacitor C charged to 20 V are
connected to each other, with the two positive plates connected and the two
negative plates connected. The final potential difference across the 25-μF
capacitor is 36 V. What is the value of the capacitance of C?
a.
b.
c.
d.
e.
26.
1.0 mJ
4.4 mJ
3.2 mJ
1.4 mJ
1.7 mJ
A 15-μF capacitor and a 30-μF capacitor are connected in series, and charged to a
potential difference of 50 V. What is the resulting charge on the 30-μF capacitor?
a.
b.
c.
d.
e.
29.
20 mC
8.0 mC
10 mC
12 mC
230 mC
When a capacitor has a charge of magnitude 80 μC on each plate the potential
difference across the plates is 16 V. How much energy is stored in this capacitor
when the potential difference across its plates is 42 V?
a.
b.
c.
d.
e.
28.
43 μF
29 μF
22 μF
58 μF
63 μF
A 4.0-mF capacitor initially charged to 50 V and a 6.0-mF capacitor charged to
30 V are connected to each other with the positive plate of each connected to the
negative plate of the other. What is the final charge on the 6.0-mF capacitor?
a.
b.
c.
d.
e.
27.
83
0.70 mC
0.80 mC
0.50 mC
0.60 mC
0.40 mC
A 15-μF capacitor and a 25-μF capacitor are connected in parallel, and charged to
a potential difference of 60 V. How much energy is then stored in this capacitor
combination?
a.
b.
c.
d.
e.
50 mJ
18 mJ
32 mJ
72 mJ
45 mJ
84
30.
CHAPTER 26
A 20-μF capacitor charged to 2.0 kV and a 40-μF capacitor charged to 3.0 kV are
connected to each other, with the positive plate of each connected to the negative
plate of the other. What is the final charge on the 20-μF capacitor after the two
are so connected?
a.
b.
c.
d.
e.
31.
A 15-μF capacitor is charged to 40 V and then connected across an initially
uncharged 25-μF capacitor. What is the final potential difference across the 25-μF
capacitor?
a.
b.
c.
d.
e.
32.
15 V
24 V
18 V
21 V
40 V
A capacitor of unknown capacitance C is charged to 100 V and then connected
across an initially uncharged 60-μF capacitor. If the final potential difference
across the 60-μF capacitor is 40 V, determine C.
a.
b.
c.
d.
e.
34.
12 V
18 V
15 V
21 V
24 V
A 30-μF capacitor is charged to 40 V and then connected across an initially
uncharged 20-μF capacitor. What is the final potential difference across the 30-μF
capacitor?
a.
b.
c.
d.
e.
33.
53 mC
27 mC
40 mC
80 mC
39 mC
49 μF
32 μF
40 μF
90 μF
16 μF
A 30-μF capacitor is charged to 80 V and then connected across an initially
uncharged capacitor of unknown capacitance C. If the final potential difference
across the 30-μF capacitor is 20 V, determine C.
a.
b.
c.
d.
e.
60 μF
75 μF
45 μF
90 μF
24 μF
Capacitance and Dielectrics
35.
A 30-μF capacitor is charged to an unknown potential V0 and then connected
across an initially uncharged 10-μF capacitor. If the final potential difference
across the 10-μF capacitor is 20 V, determine V0.
a.
b.
c.
d.
e.
36.
13 V
27 V
20 V
29 V
60 V
A parallel plate capacitor of capacitance C0 has plates of area A with separation d
between them. When it is connected to a battery of voltage V0, it has charge of
magnitude Q0 on its plates. It is then disconnected from the battery and the
plates are pulled apart to a separation 2d without discharging them. After the
plates are 2d apart, the magnitude of the charge on the plates and the potential
difference between them are
a.
b.
c.
d.
e.
37.
85
1
1
Q0, V0
2
2
1
Q0, V0
2
Q0, V0
Q0, 2V0
2Q0, 2V0
A parallel plate capacitor of capacitance C0 has plates of area A with separation d
between them. When it is connected to a battery of voltage V0, it has charge of
magnitude Q0 on its plates. It is then disconnected from the battery and the plates
are pulled apart to a separation 2d without discharging them. After the plates are
2d apart, the new capacitance and the potential difference between the plates are
a.
b.
c.
d.
e.
1
1
C0, V0
2
2
1
C0, V0
2
1
C0, 2V0
2
C0, 2V0
2C0, 2V0
86
38.
CHAPTER 26
A parallel plate capacitor of capacitance C0 has plates of area A with separation d
between them. When it is connected to a battery of voltage V0, it has charge of
magnitude Q0 on its plates. The plates are pulled apart to a separation 2d while
the capacitor remains connected to the battery. After the plates are 2d apart, the
magnitude of the charge on the plates and the potential difference between them
are
a.
b.
c.
d.
e.
39.
A parallel plate capacitor of capacitance C0 has plates of area A with separation d
between them. When it is connected to a battery of voltage V0, it has charge of
magnitude Q0 on its plates. The plates are pulled apart to a separation 2d while
the capacitor remains connected to the battery. After the plates are 2d apart, the
capacitance of the capacitor and the magnitude of the charge on the plates are
a.
b.
c.
d.
e.
40.
1
1
Q0, V0
2
2
1
Q0, V0
2
Q0, V0
2Q0, V0
2Q0, 2V0
1
1
C0, Q0
2
2
1
C0, Q0
2
C0, Q0
2C0, Q0
2C0, 2Q0
A parallel plate capacitor of capacitance C0 has plates of area A with separation d
between them. When it is connected to a battery of voltage V0, it has charge of
magnitude Q0 on its plates. While it is connected to the battery the space between
the plates is filled with a material of dielectric constant 3. After the dielectric is
added, the magnitude of the charge on the plates and the potential difference
between them are
a.
b.
c.
d.
e.
1
1
Q0, V0
3
3
1
Q0, V0
3
Q0, V0
3Q0, V0
3Q0, 3V0
Capacitance and Dielectrics
41.
A parallel plate capacitor of capacitance C0 has plates of area A with separation d
between them. When it is connected to a battery of voltage V0, it has charge of
magnitude Q0 on its plates. While it is connected to the battery, the space
between the plates is filled with a material of dielectric constant 3. After the
dielectric is added, the magnitude of the charge on the plates and the new
capacitance are
a.
b.
c.
d.
e.
42.
1
1
Q0, C0
3
3
1
Q0, C0
3
Q0, C0
3Q0, C0
3Q0, 3C0
The equivalent capacitance of the circuit shown below is
a
C
2C
C
b
a.
b.
c.
d.
e.
43.
0.2 C.
0.4 C.
1 C.
4 C.
5 C.
The equivalent capacitance of the circuit shown below is
a
a.
b.
c.
d.
e.
44.
87
C
2C
C
b
0.2 C.
0.4 C.
1 C.
4 C.
5 C.
The equivalent capacitance of the circuit shown below is
a
2C
C
b
a.
b.
c.
d.
e.
0.50 C.
1.0 C.
1.5 C.
2.0 C.
2.5 C.
C
88
45.
CHAPTER 26
Which of the following is not a capacitance?
a.
ε0A
b.
κε 0 A
c.
d.
e.
46.
d
ab
k e (b − a)
A
2k e ln(b a)
k eε 0 A
d
A parallel plate capacitor of capacitance C0 has plates of area A with separation d
between them. When it is connected to a battery of voltage V0, it has charge of
magnitude Q0 on its plates. It is then disconnected from the battery and the space
between the plates is filled with a material of dielectric constant 3. After the
dielectric is added, the magnitudes of the charge on the plates and the potential
difference between them are
a.
b.
c.
d.
e.
47.
d
1
1
Q0 , V0 .
3
3
1
Q0 , V0 .
3
Q0 , V0 .
Q0 , 3V0 .
3Q0 , 3V0 .
A parallel plate capacitor of capacitance C0 has plates of area A with separation d
between them. When it is connected to a battery of voltage V0, it has charge of
magnitude Q0 on its plates. It is then disconnected from the battery and the space
between the plates is filled with a material of dielectric constant 3. After the
dielectric is added, the magnitudes of the capacitance and the potential
difference between the plates are
a.
b.
c.
d.
e.
1
1
C0 , V0 .
3
3
1
C0 , V0 .
3
C0 , V0 .
1
3C0 , V0 .
3
3C0 , 3V0 .
Capacitance and Dielectrics
48.
An initially uncharged parallel plate capacitor of capacitance C is charged to
potential V by a battery. The battery is then disconnected. Which statement is
correct?
a.
b.
c.
d.
e.
49.
1.33 V
7.34 V
8.67 V
1,330 V
8,670 V
A 0.16 pF parallel-plate capacitor is charged to 10 V. Then the battery is
disconnected from the capacitor. When 1.00 × 10 7 electrons are now placed on
the negative plate of the capacitor, the voltage between the plates changes by
a.
b.
c.
d.
e.
51.
There is no charge on either plate of the capacitor.
The capacitor can be discharged by grounding any one of its two plates.
Charge is distributed evenly over both the inner and outer surfaces of the
plates.
The magnitude of the electric field outside the space between the plates is
approximately zero.
The capacitance increases when the distance between the plates increases.
A 0.120 pF parallel-plate capacitor is charged to a potential difference of 10.0 V
and then disconnected from the battery. A cosmic ray burst creates 1.00 × 10 6
electrons and 1.00 × 10 6 positive charges between the plates. If the charges do
not recombine, but reach the oppositely charged plates, by how much is the
potential difference between the capacitor plates reduced?
a.
b.
c.
d.
e.
50.
89
−8.9 V .
−1.1 V .
0 V.
+1.1 V .
+8.9 V .
A 0.16 pF parallel-plate capacitor is charged to 10 V. Then the battery is
disconnected from the capacitor. When 1.00 × 10 7 positive charges of magnitude
| e | are now placed on the positive plate of the capacitor, the voltage between the
plates changes by
a.
b.
c.
d.
e.
−8.9 V .
−1.1 V .
0 V.
+1.1 V .
+8.9 V .
90
52.
CHAPTER 26
A parallel plate capacitor is charged to voltage V and then disconnected from the
battery. Leopold says that the voltage will decrease if the plates are pulled apart.
Gerhardt says that the voltage will remain the same. Which one, if either, is
correct, and why?
a.
b.
c.
d.
e.
53.
Addition of a metal slab of thickness a between the plates of a parallel plate
capacitor of plate separation d is equivalent to introducing a dielectric with
dielectric constant κ between the plates. The value of κ is
a.
b.
c.
d.
e.
54.
Gerhardt, because the maximum voltage is determined by the battery.
Gerhardt, because the charge per unit area on the plates does not change.
Leopold, because charge is transferred from one plate to the other when the
plates are separated.
Leopold, because the force each plate exerts on the other decreases when the
plates are pulled apart.
Neither, because the voltage increases when the plates are pulled apart.
d−a
.
d
d.
d − a.
d
.
d−a
d
.
a
A parallel plate capacitor is connected to a battery and charged to voltage V.
Leah says that the charge on the plates will decrease if the distance between the
plates is increased while they are still connected to the battery. Gertie says that
the charge will remain the same. Which one, if either, is correct, and why?
a.
b.
c.
d.
e.
Gertie, because the maximum voltage is determined by the battery.
Gertie, because the capacitance of the capacitor does not change.
Leah, because the capacitance decreases when the plate separation is
increased.
Leah, because the capacitance increases when the plate separation is
increased.
Neither, because the charge increases when the plate separation is
increased.
Capacitance and Dielectrics
91
Open-Ended Problems
55.
Is it feasible to construct an air-filled parallel-plate capacitor that has its two
plates separated by 0.10 mm and has a capacitance of 1.0 F?
56.
Regarding the Earth and a cloud layer 800 m above the Earth as the “plates” of a
capacitor, calculate the capacitance if the cloud layer has an area of 1.0 km2. If an
electric field of 2.0 × 106 N/C makes the air break down and conduct electricity
(lightning), what is the maximum charge the cloud can hold?
57.
An electron is released from rest at the negative plate of a parallel plate capacitor.
If the distance between the plates is 5 mm and the potential difference across the
plates is 5 V, with what velocity does the electron hit the positive plate?
(me = 9.1 × 10–31 kg, qe = 1.6 × 10–19 C.)
58.
A 200-volt battery is connected to a 0.50-microfarad parallel-plate, air-filled
capacitor. Now the battery is disconnected, with care taken not to discharge the
plates. Some Pyrex glass is then inserted between the plates, completely filling
up the space. What is the final potential difference between the plates? (The
dielectric constant for Pyrex is κ = 5.6.)
92
CHAPTER 26
Capacitance and Dielectrics
Chapter 26
Capacitance and Dielectrics
1.
d
31.
c
2.
c
32.
b
3.
b
33.
c
4.
d
34.
d
5.
d
35.
b
6.
b
36.
d
7.
a
37.
c
8.
b
38.
b
9.
c
39.
a
10.
d
40.
d
11.
c
41.
e
12.
d
42.
d
13.
b
43.
b
14.
a
44.
b
15.
d
45.
e
16.
d
46.
b
17.
c
47.
d
18.
d
48.
d
19.
b
49.
a
20.
c
50.
d
21.
d
51.
d
22.
b
52.
e
23.
a
53.
d
24.
b
54.
c
25.
c
55.
26.
d
No. Each plate would have an
area of 1.1 × 107 m2
27.
b
56.
11.1 nF, 17.7 C
28.
c
57.
1.33 × 106 m/s
29.
d
58.
36 V
30.
b
93
94
CHAPTER 26