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516 ⏐⏐⏐ INDUCTORS
E
E
E
36 V
24 V
R 1
12 k�
16 V
R 2 4 k� R 4 1.5 k�
R 3
+20 V
– 6 V
3 k�
FIG. 12.79
Problem 24.
i L
L 5 mH
+ vR1 –
R 1
100 �
+
vL –
R2 470 � L 0.6 H
+
vL –
FIG. 12.80
Problem 25.
R 3
–
20 �
vR3 +
FIG. 12.81
Problems 26 and 27.
R 1
4.7 k�
R 3
+
v L
–
i L
2 M�
L 5 H
1 k�
R 2
3.3 k�
(t = 0 s)
FIG. 12.82
Problem 28.
L
i L
i L
2 H
+ –
+
vL –
*24. a. Determine the mathematical expressions for i L and v L
following the closing of the switch in Fig. 12.79.
b. Determine i L and v L after two time constants of the
storage phase.
c. Write the mathematical expressions for the current i L
and the voltage v L if the switch is opened at the
instant defined by part (b).
d. Sketch the waveforms of i L and v L for parts (a) and (c).
*25. For the network of Fig. 12.80, the switch is closed at
t � 0s.
a. Determine v L at t � 25 ms.
b. Find v L at t � 1 ms.
c. Calculate v R1 at t � 1t.
d. Find the time required for the current i L to reach
100 mA.
*26. The switch for the network of Fig. 12.81 has been closed
for about 1 h. It is then opened at the time defined as t �
0s.
a. Determine the time required for the current i R to drop
to 1 mA.
b. Find the voltage v L at t � 1 ms.
c. Calculate v R3 at t � 5t.
27. The network of Fig. 12.81 employs a DMM with an
internal resistance of 10 M� in the voltmeter mode. The
switch is closed at t � 0 s.
a. Find the voltage across the coil the instant after the
switch is closed.
b. What is the final value of the current iL? c. How much time must pass before iL reaches 10 mA?
d. What is the voltmeter reading at t � 12 ms?
*28. The switch in Fig. 12.82 has been open for a long time.
It is then closed at t � 0 s.
a. Write the mathematical expression for the current iL and the voltage vL after the switch is closed.
b. Sketch the waveform of iL and vL from the initial
value to the steady-state level.