Top most asked AC Fundamentals MCQs - SET1

Top most asked AC Fundamentals MCQs - SET1

Q1. The peak value of a sine wave is 200 V. Its average value is 

(a) 127.4 V 

(b) 141.4 V 

(c) 282.8 V 

(d)200V 

Ans: a

Q2. Two waves of the same frequency have opposite phase when the phase angle between them is 

(a) 360° 

(b) 180° 

(c) 90° 

(d) 0° 

Ans: b

Q3. The power consumed in a circuit element will be least when the phase difference between the current and voltage is 

(a) 180″ 

(b) 90° 

(c) 60° 

(d) 0° 

Ans: b

Q4. The phase difference between voltage and current wave through a circuit element is given as 30°. The essential condition is that 

(a) both waves must have same frequency 

(b) both waves must have identical peak values 

(c) both waves must have zero value at the same time 

(d) none of the above 

Ans: a

Q5. The best place to install a capacitor is 

(a) very near to inductive load 

(b) across the terminals of the inductive load 

(c) far away from the inductive load 

(d) any where 

Ans: b

Q6. Power factor of an electrical circuit is equal to

(a) R/Z

(b) Ratio of useful current to total current Iw/I

(c) Cosine of phase angle difference between current and voltage

(d) All of the above

Ans: d

Q7. The time constant of  a series R-C circuit is given by

(a) RC

(b) RC/2

(c) RC2

(d) R2C

Ans: a

Q8. The double energy transient occur in the 

(a) purely inductive circuit 

(b) R-L circuit 

(c) R-C circuit 

(d) R-L-C circuit 

Ans: d

Q9. Pure inductive circuit 

(a) consumes some power on average 

(b) does not take power at all from a line 

(c) takes power from the line during some part of the cycle and then returns back to it during other part of the cycle 

(d) none of the above 

Ans: c

Q10. Inductance affects the direct current flow 

(a) only at the time of turning off 

(b) only at the time of turning on 

(c) at the time of turning on and off 

(d) at all the time of operation 

Ans: c

Q11. A sine wave has a frequency of 50 Hz. Its angular frequency is _______ radian/second.

(a) 100 n

(b) 50 jt

(c) 25 JT

(d) 5 n

Ans: a

Q12. The reactance offered by a capacitor to alternating current of frequency 50 Hz is 20 Q. If frequency is increased to 100 Hz, reactance becomes_____ohms.

(a) 2.5

(b) 5

(c) 10

(d) 15

Ans: c

Q13. The period of a wave is

(a) the same as frequency

(6) time required to complete one cycle

(c) expressed in amperes

(d) none of the above

Ans: b

Q14. The form factor is the ratio of

(a) peak value to r.m.s. value

(6) r.m.s. value to average value

(c) average value to r.m.s. value

(d) none of the above

Ans: b

Q15. The period of a sine wave is _____ seconds.

Its frequency is

(a) 20 Hz

(b) 30 Hz

(c) 40 Hz

(d) 50 Hz

Ans: d

Q16. A heater is rated as 230 V, 10 kW, A.C. The value 230 V refers to

(a) average voltage

(b) r.m.s. voltage

(c) peak voltage

(d) none of the above

Ans: b

Q17. If two sinusoids of the same frequency but of different amplitudes and phase angles are subtracted, the resultant is

(a) a sinusoid of the same frequency

(b) a sinusoid of half the original frequency

(c) a sinusoid of double the frequency

(d) not a sinusoid

Ans: a

Q18. The peak value of a sine wave is 200 V. Its average value is

(a) 127.4 V

(b) 141.4 V

(c) 282.8 V

(d)200V

Ans: a

Q19. If two sine waves of the same frequency have a phase difference of JT radians, then

(a) both will reach their minimum values at the same instant

(b) both will reach their maximum values at the same instant

(c) when one wave reaches its maxi¬mum value, the other will reach its minimum value

(d) none of the above

Ans: c

Q20. The voltage of domestic supply is 220V. This figure represents

(a) mean value

(b) r.m.s. value

(c) peak value

(d) average value

Ans: a

Q21. Two waves of the same frequency have opposite phase when the phase angle between them is

(a) 360°

(b) 180°

(c) 90°

(d) 0°

Ans: b

Q22. The power consumed in a circuit element will be least when the phase difference between the current and voltage is

(a) 180″

(b) 90°

(c) 60°

(d) 0°

Ans: b

Q23. The r.m.s. value and mean value is the same in the case of

(a) triangular wave

(6) sine wave

(c) square wave

(d) half wave rectified sine wave

Ans: c

Q24. For the same peak value which of the following wave will ‘have the highest r.m.s. value ?

(a) square wave

(b) half wave rectified sine wave

(c) triangular wave

(d) sine wave

Ans: a

Q25. For the same peak value, which of the following wave has the least mean value ?

(a) half wave rectified sine wave

(b) triangular wave

(c) sine wave

(d) square wave

Ans: a

Q26. For a sine wave with peak value Imax the r.m.s. value is

(a) 0.5 Imax

(b) 0.707

(c) 0.9

(d) 1.414 Lmax

Ans: b

Q27. Form Factor is the ratio of

(a) average value/r.m.s. value

(b) average value/peak value

(e) r.m.s. value/average value

(d) r.m.s. value/peak value

Ans: c

Q28. Form factor for a sine wave is

(a) 1.414

(b) 0.707

(c) 1.11

(d) 0.637

Ans: c

Q29. For a sine wave with peak value Emax______8.30. the average value is

(a) 0.636 Emax

(b) 0.707 Emax

(c) 0.434 EWc

(d) lAUEmax

Ans: a

Q30. For a frequency of 200 Hz, the time period will be

(a) 0.05 s

(b) 0.005 s

(c) 0.0005 s

(d) 0.5 s

Ans: b

Q31. The phase difference between voltage and current wave through a circuit element is given as 30°. The essential condition is that

(a) both waves must have same frequency

(b) both waves must have identical peak values

(c) both waves must have zero value at the same time

(d) none of the above

Ans: a

Q32. The r.m.s. value of a sinusoidal A.C. current is equal to its value at an angle of______degrees.

(a) 90

(b) 60

(c) 45

(d) 30

Ans: c

Q33. Capacitive reactance is more when

(a) capacitance is less and frequency of supply is less

(b) capacitance is less and frequency of supply is more

(c) capacitance is more and frequency of supply is less

(d) capacitance is more and frequency of supply is more

Ans: a

Q34. In a series resonant circuit, the impedance of the circuit is

(a) minimum

(b) maximum

(c) zero

(d) none of the above

Ans: a

Q35. Power factor of an electrical circuit is equal to

(a) R/Z

(b) cosine of phase angle difference be-tween current and voltage

(c) kW/kVA

(d) all above

Ans: d

Q36. The best place to install a capacitor is

(a) very near to inductive load

(b) across the terminals of the inductive load

(c) far away from the inductive load

(d) any where

Ans: b

Q37. Poor power factor

(a) reduces load handling capability of electrical system

(b) results in more power losses in the electrical system

(c) overloads alternators, transformers and distribution lines

(d) results in more voltage drop in the line

(e) results in all above

Ans: e

Q38. Capacitors for power factor correction are rated in

(a) kW

(b) kVA

(c) kV

(d) kVAR

Ans: d

Q39. In series resonant circuit, increasing inductance to its twice value and reducing capacitance to its half value

(a) will change the maximum value of current at resonance

(6) will change the resonance frequency

(c) will change the impedance at resonance frequency

(d) will increase the selectivity of the circuit

Ans: d

Q40. Pure inductive circuit

(a) consumes some power on average

(b) does not take power at all from a line

(c) takes power from the line during some part of the cycle and then returns back to it during other part of the cycle

(d) none of the above

Ans: c

Q41. Inductance affects the direct current flow

(a) only at the time of turning off

(b) only at the time of turning on

(c) at the time of turning on and off

(d) at all the time of operation

Ans: c

Q42. Inductance of a coil Varies

(a) directly as the cross-sectional area of magnetic core

(b) directly as square of number of turns

(c) inversely as the length of the iron path

(d) as (a) to (c)

Ans: d

Q43. All the rules and laws of D.C. circuit also apply to A.C. circuit containing

(a) capacitance only

(b) inductance only

(c) resistance only

(d) all above

Ans: c

Q44. Time constant of an inductive circuit

(a) increases with increase of inductance and decrease of resistance

(b) increases with the increase of inductance and the increase of resistance

(c) increases with decrease of inductance and decrease of resistance

(d) increases with decrease of inductance and increase of resistance

Ans: a

Q45. Power factor of an inductive circuit is usually improved by connecting capacitor to it in

(a) parallel

(b) series

(c) either (a) or (b)

(d) none of the above

Ans: a

Q46. In a highly capacitive circuit the

(a) apparent power is equal to the actual power

(b) reactive power is more than the apparent power

(c) reactive power is more than the actual power

(d) actual power is more than its reactive power

Ans: c

Q47. Power factor of the following circuit will be zero

(a) resistance

(b) inductance

(c) capacitance

(d) both (b) and (c)

Ans: d

Q48. Power factor of the following circuit will be unity

(a) inductance

(b) capacitance

(c) resistance

(d) both (a) and (b)

Ans: c

Q49. Power factor of the system is kept high

(a) to reduce line losses

(b) to maximize the utilization of the capacities of generators, lines and transformers

(c) to reduce voltage regulation of the line

(d) due to all above reasons

Ans: d

Q50. The time constant of the capacitance circuit is defined as the time during which voltage

(a) falls to 36.8% of its final steady value

(b) rises to 38.6% of its final steady value

(c) rises to 63.2% of its final steady value

(d) none of the above

Ans: c

for more questions visit : Top most asked AC Fundamentals MCQs - SET 2

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These are most asked AC Fundamentals mcqs with answers and most important AC fundamental  interview and Viva question.

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