Review Questions

9.1 Which of the following is not a right way to express the sinusoid A cos ωt?

(a) A cos 2π ft (b) A cos(2πt∕T) (c) A cos ω(t − T) (d) A sin(ωt − 90°)

9.2 A function that repeats itself after fixed intervals is said to be:

(a) a phasor	(b) harmonic
(c) periodic	(d) reactive

9.3 Which of these frequencies has the shorter period?

(a) 1 krad/s (b) 1 kHz

9.4 If v1 = 30 sin(ωt + 10°) and v2 = 20 sin(ωt + 50°), which of these statements are true?
- (a) v1 leads v2 (b) v2 leads v¹ (c) v2 lags v1 (d) v1 lags v²
- (e) v1 and v2 are in phase
9.5 The voltage across an inductor leads the current through it by 90°.

(a) True (b) False

9.6 The imaginary part of impedance is called:
- (a) resistance (b) admittance (c) susceptance (d) conductance
- (e) reactance
9.7 The impedance of a capacitor increases with increasing frequency.

(a) True (b) False

9.8 At what frequency will the output voltage vo(t) in Fig. 9.39 be equal to the input voltage v(t) ?

(a) 0 rad/s	(b) 1 rad/s	(c) 4 rad/s
(d) ∞ rad/s	(e) none of the above

Figure 9.39

For Review Question 9.8.

9.9 A series RC circuit has ∣VR∣ = 12 V and ∣VC∣ = 5 V. The magnitude of the supply voltage is:

(a) −7 V (b) 7 V (c) 13 V (d) 17 V

9.10 A series RCL circuit has R = 30 Ω, XC = 50 Ω, and XL = 90 Ω. The impedance of the circuit is:

(a) 30 + j140 Ω (b) 30 + j40 Ω (c) 30 − j40 Ω (d) −30 − j40 Ω (e) −30 + j40 Ω

Answers: 9.1d, 9.2c, 9.3b, 9.4b,d, 9.5a, 9.6e, 9.7b, 9.8d, 9.9c, 9.10b.

9.1 Given the sinusoidal voltage v(t) = 50 cos (30t + 10°) V, find: (a) the amplitude Vm, (b) the period T, (c) the frequency f, and (d) v(t) at t = 10 ms.
9.2 A current source in a linear circuit has

is = 15 cos (25 π t + 25°) A