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250 ⏐⏐⏐ SERIES-PARALLEL NETWORKS
240 V
R T
I
+
V
–
R 1
3 �
+
R 2
V 3
–
5 �
R 3
8 �
18 V
3 � 6 �
FIG. 7.84
Problem 21.
FIG. 7.86
Problem 23.
R 4
2 �
+
4 � V5 –
FIG. 7.88
Problem 25.
I
20 V
R 6
R5 6 �
1 �
+
V7 R7 2 �
–
I7 S
S P P
*21. For the network of Fig. 7.84:
a. Determine the current I.
b. Calculate the open-circuit voltage V.
*22. For the network of Fig. 7.85, find the resistance R3 if the
current through it is 2 A.
120 V
R 2
FIG. 7.85
Problem 22.
R 1
20 � R 3
12 �
*23. If all the resistors of the cube in Fig. 7.86 are 10 �, what
is the total resistance? (Hint: Make some basic assumptions
about current division through the cube.)
*24. Given the voltmeter reading V � 27 V in Fig. 7.87:
a. Is the network operating properly?
b. If not, what could be the cause of the incorrect reading?
6 k�
E 45 V
36 k�
FIG. 7.87
Problem 24.
V
12 k�
6 k�
2 A
= 27 V
SECTION 7.3 Ladder Networks
25. For the ladder network of Fig. 7.88:
a. Find the current I.
b. Find the current I7. c. Determine the voltages V3, V5, and V7. d. Calculate the power delivered to R7, and compare it to
the power delivered by the 240-V supply.