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PROBLEMS
SECTION 21.2 Mutual Inductance
1. For the air-core transformer of Fig. 21.55:
a. Find the value of Ls if the mutual inductance M is
equal to 80 mH.
b. Find the induced voltages ep and es if the flux linking
the primary coil changes at the rate of 0.08 Wb/s.
c. Find the induced voltages ep and es if the current ip changes at the rate of 0.3 A/ms.
2. a. Repeat Problem 1 if k is changed to 1.
b. Repeat Problem 1 if k is changed to 0.2.
c. Compare the results of parts (a) and (b).
3. Repeat Problem 1 for k � 0.9, Np � 300 turns, and Ns �
25 turns.
SECTION 21.3 The Iron-Core Transformer
4. For the iron-core transformer (k � 1) of Fig. 21.56:
a. Find the magnitude of the induced voltage Es. b. Find the maximum flux �m. 5. Repeat Problem 4 for Np � 240 and Ns � 30.
6. Find the applied voltage of an iron-core transformer if
the secondary voltage is 240 V, and Np � 60 with Ns �
720.
7. If the maximum flux passing through the core of Problem
4 is 12.5 mWb, find the frequency of the input
voltage.
FIG. 21.54
The output file for the analysis indicated in Fig. 21.53.
Ip +
Ep = 25 V
–
f = 60 Hz
i p
N p = 8
L p = 50 mH N s = 80
+
e p
–
N p = 20 L s
k = 0.8
+
e s
–
FIG. 21.55
Problems 1, 2, and 3.
Φ m
Φ m
FIG. 21.56
Problems 4, 5, and 7.
PROBLEMS ⏐⏐⏐ 971
N s = 64
+ Is Es –