Alternating Current MCQ Questions and Answers for Practice

1. An a.c. supply is 70.7 V, 50 Hz. Which of the following statements is false?

1. The periodic time is 20 ms
2. The peak value of the voltage is 70.7 V
3. The r.m.s. value of the voltage is 70.7 V
4. The peak value of the voltage is 100 V

2. An alternating current completes 100 cycles in 0.1 s. Its frequency is

1. 20 Hz
2. 100 Hz
3. 0.002 Hz
4. 1 kHz

3. An alternating voltage of maximum value 100 V is applied to a lamp. Which of the following directvoltages, if applied to the lamp, would cause the lamp to light with the same brilliance?

1. 100 V
2. 63.7 V
3. 70.7 V
4. 141.4 V

4. State which of the following is false. For a sine wave

1. the peak factor is 1.414
2. the r.m.s. value is 0.707 × peak value
3. the average value is 0.637 × r.m.s. value
4. the form factor is 1.11

5. The number of complete cycles of an alternating current occurring in one second is known as

1. the maximum value of the alternating current
2. the frequency of the alternating current
3. the peak value of the alternating current
4. the r.m.s. or effective value

6. The supply of electrical energy for a consumer is usually by a.c. because

1. transmission and distribution are more easily effected
2. it is most suitable for variable speed motors
3. the volt drop in cables is minimal
4. cable power losses are negligible

7. The value normally stated when referring to alternating currents and voltages is the

1. instantaneous value
2. r.m.s. value
3. average value
4. peak value

8. The value of an alternating current at any given instant is

1. a maximum value
2. a peak value
3. an instantaneous value
4. an r.m.s. value

9. Which of the following statements is false?

1. It is cheaper to use a.c. than d.c.
2. Distribution of a.c. is more convenient than with d.c. since voltages may be readily altered using transformers
3. An alternator is an a.c. generator
4. A rectifier changes d.c. to a.c.