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a c fundamentals circuits and circuit theory MCQs

Practise focused a c fundamentals circuits and circuit theory questions with marked answers for exam preparation and subject revision.

a c fundamentals circuits and circuit theory Mcqs
1. The peak value of a sine wave is 200 V. Its average value is___________?
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A. 127.4 V

B. 200V

C. 141.4 V

D. 282.8 V

2. In a series resonant circuit, the impedance of the circuit is___________?
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A. maximum

B. minimum

C. none of the above

D. zero

3. In a highly capacitive circuit the__________?
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A. reactive power is more than the apparent power

B. reactive power is more than the actual power

C. actual power is more than its reactive power

D. apparent power is equal to the actual power

4. The r.m.s. value of a sinusoidal A.C. current is equal to its value at an angle of_______degrees?
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A. 30

B. 90

C. 60

D. 45
5. In a circuit containing R, L and C, power loss can take place in____________?
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A. L only

B. C only

C. all above

D. R only
6. Two waves of the same frequency have opposite phase when the phase angle between them is_________?
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A. 90

B. 360

C. 0

D. 180
7. Power factor of an inductive circuit is usually improved by connecting capacitor to it in____________?
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A. series

B. parallel

C. none of the above

D. either A. or (b)

8. The power consumed in a circuit element will be least when the phase difference between the current and voltage is__________?
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A. 0

B. 60

C. 90

D. 180?

9. Form factor for a sine wave is________?
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A. 1.414

B. 1.11

C. 0.637

D. 0.707

10. For the same peak value which of the following wave will have the highest r.m.s. value?
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A. sine wave

B. triangular wave

C. half wave rectified sine wave

D. square wave
11. For a sine wave with peak value Emax _______ 8.30. the average value is?
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A. 0.434 EWc

B. lAUEmax

C. 0.636 Emax

D. 0.707 Emax

12. The form factor is the ratio of_______?
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A. peak value to r.m.s. value

B. none of the above

C. r.m.s. value to average value

D. average value to r.m.s. value

13. The double energy transient occur in the____________?
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A. R-L-C circuit

B. R-C circuit

C. purely inductive circuit

D. R-L circuit

14. For the same peak value, which of the following wave has the least mean value ?
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A. half wave rectified sine wave

B. sine wave

C. square wave

D. triangular wave

15. Power factor of an electrical circuit is equal to____________?
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A. all of these

B. cosine of phase angle difference be-tween current and voltage

C. ratio of useful current to total current Iw/I

D. R/Z

E. kW/kVA

16. Power factor of the following circuit will be zero__________?
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A. resistance

B. inductance

C. capacitance

D. both B. and C.
17. All the rules and laws of D.C. circuit also apply to A.C. circuit containing_____________?
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A. all above

B. capacitance only

C. resistance only

D. inductance only

18. Pure inductive circuit____________?
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A. does not take power at all from a line

B. none of the above

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. consumes some power on average

19. In a pure inductive circuit___________?
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A. the current lags behind the voltage by 90

B. the current is in phase with the voltage

C. the current can lead or lag by 90

D. the current leads the voltage by 90

20. For a sine wave with peak value Imax the r.m.s. value is_______?
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A. 0.9

B. 0.707

C. 0.5 Imax

D. 1.414 Lmax

21. For a frequency of 200 Hz, the time period will be__________?
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A. 0.005 s

B. 0.5 s

C. 0.0005 s

D. 0.05 s

22. In series resonant circuit, increasing inductance to its twice value and reducing capacitance to its half value__________?
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A. will change the resonance frequency

B. will increase the selectivity of the circuit

C. will change the maximum value of current at resonance

D. will change the impedance at resonance frequency

23. The best place to install a capacitor is___________?
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A. any where

B. across the terminals of the inductive load

C. far away from the inductive load

D. very near to inductive load

24. The product of apparent power and cosine of the phase angle between circuit voltage and current is
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A. volt-amperes

B. true power

C. reactive power

D. instantaneous power

25. 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?
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A. 10

B. 2.5

C. 5

D. 15

26. The time constant of the capacitance circuit is defined as the time during which voltage________?
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A. none of the above

B. falls to 36.8% of its final steady value

C. rises to 63.2% of its final steady value

D. rises to 38.6% of its final steady value

27. The power factor at resonance in R-L- C parallel circuit is________?
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A. zero

B. 0.08 lagging

C. 0.8 leading

D. unity
28. The square waveform of current has following relation between r.m.s. value and average value?
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A. r.m.s. value of current is less than average value

B. r.m.s. value of current is greater than average value

C. none of the above

D. r.m.s. value is equal to average value
29. The voltage of domestic supply is 220V. This figure represents__________?
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A. peak value

B. mean value

C. r.m.s. value

D. average value

30. When an alternating current passes through an ohmic resistance the electrical power converted into heat is__________?
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A. none of the above

B. reactive power

C. true power

D. apparent power

31. In each of the three coils of a three phase generator, an alternating voltage having an r.m.s. value of 220 V is induced. Which of the following values is indicated by the voltmeters ______?
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A. 220 V

B. 220/V3 V

C. none of the above

D. 220V3V

32. The r.m.s. value of alternating current is given by steady (D.C.) current which when flowing through a given circuit for a given time produces__________?
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A. the same heat as produced by A.C. when flowing through the same circuit

B. the less heat than produced by A.C. flowing through the same circuit

C. the more heat than produced by A.C. when flowing through the same circuit

D. none of the above

33. The period of a wave is___________?
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A. none of the above

B. the same as frequency

C. time required to complete one cycle

D. expressed in amperes

34. A pure capacitor connected across an A.C. voltage consumed 50 W. This is due to________?
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A. the current flowing in capacitor

B. the size of the capacitor being quite big

C. the capacitive reactance in ohms

D. the statement is incorrect
35. The power consumed in a circuit element will be least when the phase difference between the current and voltage is________?
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A. 90

B. 0

C. 180?

D. 60

36. The transient currents are associated with the____________?
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A. applied voltage to the circuit

B. resistance of the circuit

C. impedance of the circuit

D. changes in the stored energy in the inductors and capacitors
37. Poor power factor________?
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A. overloads alternators, transformers and distribution lines

B. results in all above

C. reduces load handling capability of electrical system

D. results in more voltage drop in the line

E. results in more power losses in the electrical system

38. The r.m.s. value and mean value is the same in the case of___________?
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A. triangular wave

B. square wave

C. half wave rectified sine wave

D. sine wave

39. In a pure resistive circuit__________?
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A. current is in phase with the voltage

B. current leads the voltage by 90

C. current can lead or lag the voltage by 90

D. current lags behind the voltage by 90

40. Power factor of the following circuit will be unity
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A. inductance

B. capacitance

C. resistance

D. both A. and B.

41. Form Factor is the ratio of__________?
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A. r.m.s. value/peak value

B. r.m.s. value/average value

C. average value/r.m.s. value

D. average value/peak value

42. If two sine waves of the same frequency have a phase difference of JT radians, then_______?
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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 maximum value, the other will reach its minimum value

D. none of the above

43. Inductance affects the direct current flow__________?
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A. at the time of turning on and off

B. only at the time of turning off

C. at all the time of operation

D. only at the time of turning on

44. If two sinusoids of the same frequency but of different amplitudes and phase angles are subtracted, the resultant is____________?
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A. a sinusoid of the same frequency

B. not a sinusoid

C. a sinusoid of half the original frequency

D. a sinusoid of double the frequency

45. A sine wave has a frequency of 50 Hz. Its angular frequency is ________ radian/second.
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A. 5 n

B. 50 jt

C. 100 n

D. 25 JT

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

47. In a loss-free R-L-C circuit the transient current is__________?
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A. non-oscillating

B. square wave

C. oscillating

D. sinusoidal
48. Inductance of a coil Varies__________?
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A. directly as the cross-sectional area of magnetic core

B. inversely as the length of the iron path

C. directly as square of number of turns

D. directly as the permeability of the core

E. as A. to (d)
49. Capacitors for power factor correction are rated in_________?
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A. kVAR

B. kV

C. kW

D. kVA

50. An A.C. voltage is impressed across a pure resistance of 3.5 ohms in parallel with a pure inductance of impedance of 3.5 ohms?
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A. the current through the resistance is more

B. the current through the resistance is less

C. both resistance and inductance carry equal currents

D. none of the above