MCQ’s on AC Fundamentals| Alternating Current Objective questions

1. An a.c. current given by i = 14.14 sin (ωt +π/6) has an r.m.s value of — amperes.

(a) 10

(b) 14.14

(c) 1.96

(d) 7.07

and a phase of — degrees.

(e) 180

(f) 30

(g) − 30

(h) 210

2. If e1 = A sin ωt and e2 = B sin (ωt − φ), then (a) e1 lags e2 by θ

(b) e2 lags e1 by θ

(c) e2 leads e2 by θ

(d) e1 is in phase with e2

3. From the two voltage equations eA = Em sin 100πt and eB = Em sin (100πt + π/6), it

is obvious that

(a) A leads B by 30°

(b) B achieves its maximum value 1/600 second before A does.

(c) B lags behind A

(d) A achieves its zero value 1/600 second before B.

4. The r.m.s. value of a half-wave rectified current is 10A, its value for full-wave rectification would be — amperes.

(a) 20

(b) 14.14

(c) 20/π

(d) 40/π

5. A resultant current is made of two components : a 10 A d.c. component and a sinusoidal

component of maximum value 14.14

A. The average value of the resultant current

is — amperes.

(a) 0 (b) 24.14

(c) 10 (d) 4.14

and r.m.s. value is — amperes.

(e) 10 (f) 14.14

(g) 24.14 (h) 100

6. The r.m.s. value of sinusoidal a.c. current is equal to its value at an angle of — degree

(a) 60 (b) 45 (c) 30 (d) 90

7. Two sinusoidal currents are given by the equations : i2 = 10 sin (ωt + π/3) and i2 = 15

sin (ωt − π/4). The phase difference

between them is — degrees.

(a) 105

(b) 75

(c) 15

(d) 60

8. As sine wave has a frequency of 50 Hz. Its angular frequency is — radian/second.

(a) 50/π

(b) 50/2 π

(c) 50 π

(d) 100 π

9. An a.c. current is given by i = 100 sin 100. It will achieve a value of 50 A after — second.

(a) 1/600

(b) 1/300

(c) 1/1800

(d) 1/900

10. The reactance offered by a capacitor to alternating current of frequency 50 Hz is 10Ω. If frequency is increased to 100 Hz reactance

becomes—ohm.

(a) 20 (b) 5

(c) 2.5 (d) 40

11. A complex current wave is given by i = 5 + 5 sin 100 πt ampere. Its average value is — ampere.

(a) 10 (b) 0

(c) 50 (d) 5

Fig. 11.67

12. The current through a resistor has a waveform as shown in Fig. 11.67. The reading

shown by a moving coil ammeter will be ampere.

(a) 5/ 2 (b) 2.5/ 2

(c) 5/π (d) 5

ANSWERS

1. a, f 2. b 3. b 4. b 5. c, f 6. b 7. a 8. d 9. a 10. b 11. d 12. c