Top most asked AC Fundamentals MCQs - SET2

 

Top most asked AC Fundamentals MCQs - SET2

Q1. In a loss-free R-L-C circuit the transient current is

(a) oscillating

(b) square wave

(c) sinusoidal

(d) non-oscillating

Ans: c

Q2. 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

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

(b) the same heat as produced by A.C. when flowing through the same circuit

(c) the less heat than produced by A.C. flowing through the same circuit

(d) none of the above

Ans: b

Q3. The square waveform of current has following relation between r.m.s. value and average value.

(a) r.m.s. value is equal to average value

(b) r.m.s. value of current is greater than average value

(c) r.m.s. value of current is less than average value

(d) none of the above

Ans: a

Q4. 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

Q5. The transient currents are associated with the

(a) changes in the stored energy in the inductors and capacitors

(b) impedance of the circuit

(c) applied voltage to the circuit

(d) resistance of the circuit

Ans: a

Q6. The power factor at resonance in R-L- C parallel circuit is

(a) zero

(b) 0.08 lagging

(c) 0.8 leading

(d) unity

Ans: d

Q7. In the case of an unsymmetrical alternating current the average value must always be taken over

(a) unsymmetrical part of the wave form

(b) the quarter cycle

(c) the half cycle

(d) the whole cycle

Ans: d

Q8. In a pure resistive circuit

(a) current lags behind the voltage by 90°

(b) current leads the voltage by 90°

(c) current can lead or lag the voltage by 90°

(d) current is in phase with the voltage

Ans: d

Q9. In a pure inductive circuit

(a) the current is in phase with the voltage

(b) the current lags behind the voltage by 90°

(c) the current leads the voltage by 90°

(d) the current can lead or lag by 90°

Ans: b

Q10. In a circuit containing R, L and C, power loss can take place in

(a) C only

(b) L only

(c) R only

(d) all above

Ans: c

Q11. Inductance of coil

(a) is unaffected by the supply frequency

(b) decreases with the increase in supply frequency

(c) increases with the increase in supply frequency

(d) becomes zero with the increase in supply frequency

Ans: c

Q12. In any A.C. circuit always

(a) apparent power is more than actual power

(b) reactive power is more than apparent power

(c) actual power is more than reactive power

(d) reactive power is more than actual power

Ans: a

Q13. Which of the following circuit component opposes the change in the circuit voltage ?

(a) Inductance

(b) Capacitance

(c) Conductance

(d) Resistance

Ans: a

Q14. In a purely inductive circuit

(a) actual power is zero

(b) reactive power is zero

(c) apparent power is zero

(d) none of above is zero

Ans: a

Q15. Power factor of electric bulb is

(a) zero

(b) lagging

(c) leading

(d) unity

Ans: d

Q16. Pure inductive circuit takes power from the A.C. line when

(a) applied voltage decreases but current increases

(b) applied voltage increases but current decreases

(c) both applied voltage and current increase

(d) both applied voltage and current decrease

Ans: a

Q17. Time constant of a circuit is the time in seconds taken after the application of voltage to each

(a) 25% of maximum value

(b) 50% of maximum value

(c) 63% of maximum value

(d) 90% of the maximum value

Ans: c

Q18. 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 the decrease of inductance and decrease of resistance

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

Ans: a

Q19. Time constant of a capacitive circuit

(a) increases with the decrease of capacitance and decrease of resistance

(b) increases with the decrease of capacitance and increase of resistance

(c) increases with the increase of capacitance and decrease of resistance

(d) increase with increase of capacitance and increase of resistance

Ans: d

Q20. Magnitude of current at resonance in R-L-C circuit

(a) depends upon the magnitude of R

(b) depends upon the magnitude of L

(c) depends upon the magnitude of C

(d) depends upon the magnitude of R, Land C

Ans: a

Q21. In a R-L-C circuit

(a) power is consumed in resistance and is equal to I R

(b) exchange of power takes place between inductor and supply line

(c) exchange of power takes place between capacitor and supply line

(d) exchange of power does not take place between resistance and the supply line

(e) all above are correct

Ans: e

Q22. In R-L-C series resonant circuit magnitude of resonance frequency can be changed by changing the value of

(a) R only

(b) L only

(c)C only

(d)LorC

Ans: d

Q23. In a series L-C circuit at the resonant frequency the

(a) current is maximum

(b) current is minimum

(c) impedance is maximum

(d) voltage across C is minimum

Ans: a

Q24. The time constant of a series R-C circuit is given by

(a) R/C

(b) RC2

(c) RC

(d) R2C

Ans: c

Q25. If resistance is 20 Q. and inductance is 27 in a R-L series circuit, then time constant of this circuit will be

(a) 0.001 s

(b) 0.1 s

(c) 10 s

(d) 100 s

Ans: b

Q26. Which of the following coil will have large resonant frequency ?

(a) A coil with large resistance

(b) A coil with low resistance

(c) A coil with large distributed capacitance

(d) A coil with low distributed capacitance

Ans: c

Q27. If a sinusoidal wave has frequency of 50 Hz with 30 A r.m.s. current which of the following equation represents this wave ?

(a) 42.42 sin 3141

(b) 60 sin 25 t

(c) 30 sin 50 t

(d) 84.84 sin 25 t

Ans: a

Q28. The safest value of current the human body can carry for more than 3 second is

(a) 4 mA

(b) 9 mA

(c) 15 mA

(d) 25 mA

Ans: b

Q29. A pure inductance connected across 250 V, 50 Hz supply consumes 100 W.

This consumption can be attributed to

(a) the big size of the inductor

(b) the reactance of the inductor

(c) the current flowing in the inductor

(d) the statement given is false

Ans: d

Q30. The input of an A.C. circuit having power factor of 0.8 lagging is 40 kVA

The power drawn by the circuit is

(a) 12 kW

(b) 22 kW

(c) 32 kW

(d) 64 kW

Ans: c

Q31. The effective resistance of an iron-cored choke working on ordinary supply frequency is more than its true resistance because of

(a) iron loss in core

(b) skin effect

(c) increase in temperature

(d) capacitive effect between adjacent coil turns

Ans: a

Q32. In an AC. circuit, a low value of kVAR compared with kW indicates

(a) low efficiency

(b) high power factor

(c) unity power factor

(d) maximum load current

Ans: b

Q33. In AC. circuits, laminated iron is invariably used in order to

(a) reduce eddy current loss

(b) increase heat radiation

(c) make assembly cheap and easier

(d) reduce circuit permeability

Ans: a

Q34. The ratio of active power to apparent power is known as factor.

(a) demand

(b) load

(c) power

(d) form

Ans: c

Q35. All definitions of power factor of a series R-L-C circuit are correct except

(a) ratio of net reactance and impedance

(b) ratio of kW and kVA

(c) ratio of J and Z

(d) ratio of W and VA

Ans: a

Q36. The apparent power drawn by an A.C. circuit is 10 kVA and active power is 8 kW. The reactive power in the circuit is

(a) 4 kVAR

(b) 6 kVAR

(c) 8 kVAR

(d) 16 kVAR

Ans: b

Q37. What will be the phase angle between two alternating waves of equal frequency, when one wave attains maximum value the other is at zero value ?

(a) 0°

(b) 45°

(c) 90°

(d) 180°

Ans: c

Q38. The purpose of a parallel circuit resonance is to magnify

(a) current

(b) voltage

(c) power

(d) frequency

Ans: b

Q39. In an A.C. circuit power is dissipated in

(a) resistance only

(b) inductance only

(c) capacitance only

(d) none of the above

Ans: a

Q40. In a parallel R-C circuit, the current always______the applied voltage

(a) lags

(b) leads

(c) remains in phase with

(d) none of the above

Ans: b

Q41. At very low frequencies a series R-C circuit behaves as almost purely

(a) resistive

(b) inductive

(c) capacitive

(d) none of the above

Ans: c

Q42. Skin effect occurs when a conductor carries current at_____ frequencies.

(a) very low

(b) low

(c) medium

(d) high

Ans: d

Q43. At ______ frequencies the parallel R-L circuit behaves as purely resistive.

(a) low

(b) very low

(c) high

(d) very high

Ans: d

Q44. In a sine wave the slope is constant

(a) between 0° and 90°

(b) between 90° and 180°

(c) between 180° and 270°

(d) no where

Ans: d

Q45. The power is measured in terms of decibles in case of

(a) electronic equipment

(b) transformers

(c) current transformers

(d) auto transformers

Ans: a

Q46. Capacitive susceptance is a measure of

(a) reactive power in a circuit

(b) the extent of neutralisation of reactive power in a circuit

(c) a purely capacitive circuit’s ability to pass current

(d) a purely capacitive circuit’s ability to resist the flow of current

Ans: c

Q47. Which of the following statements pertains to resistors only ?

(a) can dissipate considerable amount of power

(6) can act as energy storage devices

(c) connecting them in parallel in¬creases the total value

(d) oppose sudden changes in voltage

Ans: a

Q48. Which of the following refers to a parallel circuit ?

(a) The current through each element is same

(b) The voltage across element is in proportion to it’s resistance value

(c) The equivalent resistance is greater than any one of the resistors

(d) The current through any one element is less than the source current

Ans: d

Q49. A parallel AC. circuit in resonance will

(a) have a high voltage developed across each inductive and capacitive section

(b) have a high impedance

(c) act like a resistor of low value

(d) have current in each section equal to the line current

Ans: b

Q50. Wire-wound resistors are unsuitable for use at high frequencies because they

(a) create more electrical noise

(b) are likely to melt under excessive eddy current heat

(c) consume more power

(d) exhibit unwanted inductive and capacitive effects

Ans: d

Please go through: Top most asked AC Fundamentals MCQs - SET1

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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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