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*47. For the network of Fig. 10.107, determine the following
100 ms after the switch is closed:
a. Vab b. Vac c. Vcb d. Vda e. If the switch is moved to position 2 one hour later,
find the time required for vR2 to drop to 20 V.
48. For the circuits of Fig. 10.108, find the voltage across and
charge on each capacitor after each capacitor has charged
to its final value.
48 V
C 1
40 mF
C 1
5 k�
2 k�
C2 0.04 mF
(a)
80 V
(b)
C2 60 mF
6 k�
FIG. 10.108
Problem 48.
0.08 mF
4 k�
4 k�
SECTION 10.14 Energy Stored by a Capacitor
49. Find the energy stored by a 120-pF capacitor with 12 V
across its plates.
50. If the energy stored by a 6-mF capacitor is 1200 J, find
the charge Q on each plate of the capacitor.
*51. An electronic flashgun has a 1000-mF capacitor that is
charged to 100 V.
a. How much energy is stored by the capacitor?
b. What is the charge on the capacitor?
c. When the photographer takes a picture, the flash fires
for 1/2000 s. What is the average current through the
flashtube?
d. Find the power delivered to the flashtube.
e. After a picture is taken, the capacitor has to be
recharged by a power supply that delivers a maximum
current of 10 mA. How long will it take to charge the
capacitor?
52. For the network of Fig. 10.109:
a. Determine the energy stored by each capacitor under
steady-state conditions.
b. Repeat part (a) if the capacitors are in series.
E
100 V
24 V
1
R 2
6 k�
2
d
40 k�
R 1
20 k�
C 2
FIG. 10.107
Problem 47.
4 k�
3 k�
FIG. 10.109
Problem 52.
PROBLEMS ⏐⏐⏐ 433
C 1
a
c
12 mF C3 b
8 mF
6 mF 12 mF
12 mF