Review Questions

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Review Questions

7.1 An RC circuit has R = 2 Ω and C = 4 F. The time constant is:

(a) 0.5 s (b) 2 s (c) 4 s (d) 8 s 15 s

7.2 The time constant for an RL circuit with R = 2 Ω and L = 4 H is:

(a) 0.5 s (b) 2 s (c) 4 s (d) 8 s 15 s

7.3 A capacitor in an RC circuit with R = 2 Ω and C = 4 F is being charged. The time required for the capacitor voltage to reach 63.2 percent of its steadystate value is:

(a) 2 s (b) 4 s (c) 8 s (d) 16 s none of the above

7.4 An RL circuit has R = 2 Ω and L = 4 H. The time needed for the inductor current to reach 40 percent of its steady-state value is:

(a) 0.5 s (b) 1 s (c) 2 s (d) 4 s none of the above

Problems 299

• 7.5 In the circuit of Fig. 7.79, the capacitor voltage just before t = 0 is:
  • (a) 10 V (b) 7 V (c) 6 V (d) 4 V 0 V

Figure 7.79

For Review Questions 7.5 and 7.6.

7.6 In the circuit in Fig. 7.79, v(∞) is:

(a)

$$10 \text{ V}$$

(b) $7 \text{ V}$ (c) $6 \text{ V}$
(d) $4 \text{ V}$ 0 V

7.7 For the circuit in Fig. 7.80, the inductor current just before t = 0 is:

(a) 8 A (b) 6 A (c) 4 A (d) 2 A 0 A

Figure 7.80

For Review Questions 7.7 and 7.8.

7.8 In the circuit of Fig. 7.80, i(∞) is:

(a) 10 A (b) 6 A (c) 4 A (d) 2 A 0 A

7.9 If vs changes from 2 V to 4 V at t = 0, we may express vs as:

(a) δ(t) V (b) 2u(t) V (c) 2u(−t) + 4u(t) V (d) 2 + 2u(t) V 4u(t) − 2 V

7.10 The pulse in Fig. 7.116(a) can be expressed in terms of singularity functions as:

(a) 2u(t) + 2u(t − 1) V	(b) 2u(t) − 2u(t − 1) V
(c) 2u(t) − 4u(t − 1) V	(d) 2u(t) + 4u(t − 1) V

Answers: 7.1d, 7.2b, 7.3c, 7.4b, 7.5d, 7.6a, 7.7c, 7.8e , 7.9c,d, 7.10b.