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972 ⏐⏐⏐ TRANSFORMERS
+
Vg = 20 V
–
+
V g
–
I p
N p
36 �
+
–
N s
FIG. 21.58
Problem 13.
I p
I L
FIG. 21.57
Problems 8 through 12.
R p
4 �
V g = 120 V ∠0°
Z L
X p
8 �
+
V L
–
Z s = R = 4 �
4 : 1
Ideal transformer
SECTION 21.4 Reflected Impedance and Power
8. For the iron-core transformer of Fig. 21.57:
a. Find the magnitude of the current IL and the voltage
VL if a � 1/5, Ip � 2 A, and ZL � 2-� resistor.
b. Find the input resistance for the data specified in
part (a).
9. Find the input impedance for the iron-core transformer of
Fig. 21.57 if a � 2, Ip � 4 A, and Vg � 1600 V.
10. Find the voltage Vg and the current Ip if the input impedance
of the iron-core transformer of Fig. 21.57 is 4 �,
and VL � 1200 V and a � 1/4.
11. If VL � 240 V, ZL � 20-� resistor, Ip � 0.05 A, and Ns �
50, find the number of turns in the primary circuit of the
iron-core transformer of Fig. 21.57.
12. a. If Np � 400, Ns � 1200, and Vg � 100 V, find the
magnitude of Ip for the iron-core transformer of Fig.
21.57 if ZL � 9 ��j 12 �.
b. Find the magnitude of the voltage VL and the current
IL for the conditions of part (a).
SECTION 21.5 Impedance Matching, Isolation,
and Displacement
13. a. For the circuit of Fig. 21.58, find the transformation
ratio required to deliver maximum power to the
speaker.
b. Find the maximum power delivered to the speaker.
SECTION 21.6 Equivalent Circuit
(Iron-Core Transformer)
14. For the transformer of Fig. 21.59, determine
a. the equivalent resistance Re. b. the equivalent reactance Xe. c. the equivalent circuit reflected to the primary.
d. the primary current for Vg � 50 V �0°.
e. the load voltage VL. f. the phasor diagram of the reflected primary circuit.
g. the new load voltage if we assume the transformer to
be ideal with a 4 : 1 turns ratio. Compare the result
with that of part (e).
X s
2 �
FIG. 21.59
Problems 14 through 16, 30, and 31.
R s
1 �
R L
+
20 � VL –