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A.C. Fundamentals, Circuits and Circuit Theory

Study 109 Electrical Engineering MCQs with correct answers and explanations.

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81Electrical EngineeringMedium

Inductance of a coil Varies________?

Adirectly as square of number of turns

Bdirectly as the cross-sectional area of magnetic core

Cdirectly as the permeability of the core

Dinversely as the length of the iron path

Eas A. to (d)

Correct answer

E. as A. to (d)

Explanation

The correct answer is as A. to (d).

82Electrical EngineeringMedium

If two sinusoids of the same frequency but of different amplitudes and phase angles are subtracted, the resultant is________?

Anot a sinusoid

Ba sinusoid of the same frequency

Ca sinusoid of half the original frequency

Da sinusoid of double the frequency

Correct answer

B. a sinusoid of the same frequency

Explanation

The correct answer is a sinusoid of the same frequency.

83Electrical EngineeringMedium

Capacitors for power factor correction are rated in________?

AkVAR

BkW

CkVA

DkV

Correct answer

A. kVAR

Explanation

The correct answer is kVAR.

84Electrical EngineeringMedium

A pure inductance connected across 250 V, 50 Hz supply consumes 100 W. This consumption can be attributed to________?

Athe current flowing in the inductor

Bthe statement given is false

Cthe reactance of the inductor

Dthe big size of the inductor

Correct answer

B. the statement given is false

Explanation

The correct answer is the statement given is false.

85Electrical EngineeringMedium

Time constant of a capacitive circuit________?

Aincreases with the decrease of capacitance and decrease of resistance

Bincrease with increase of capacitance and increase of resistance

Cincreases with the decrease of capacitance and increase of resistance

Dincreases with the increase of capacitance and decrease of resistance

Correct answer

B. increase with increase of capacitance and increase of resistance

Explanation

The correct answer is increase with increase of capacitance and increase of resistance.

86Electrical EngineeringMedium

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________?

Anone of the above

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

Cthe same heat as produced by A.C. when flowing through the same circuit

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

Correct answer

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

Explanation

The correct answer is the same heat as produced by A.C. when flowing through the same circuit.

87Electrical EngineeringMedium

Power factor of an electrical circuit is equal to________?

AkW/kVA

Bratio of useful current to total cur¬rent Iw/I

CR/Z

Dall of these

Ecosine of phase angle difference be-tween current and voltage

Correct answer

D. all of these

Explanation

The correct answer is all of these.

88Electrical EngineeringMedium

The purpose of a parallel circuit resonance is to magnify________?

Apower

Bvoltage

Cfrequency

Dcurrent

Correct answer

B. voltage

Explanation

The correct answer is voltage.

89Electrical EngineeringMedium

For a sine wave with peak value Emax ________ 8.30. the average value is?

A0.636 Emax

B0.434 EWc

ClAUEmax

D0.707 Emax

Correct answer

A. 0.636 Emax

Explanation

The correct answer is 0.636 Emax.

90Electrical EngineeringMedium

All the rules and laws of D.C. circuit also apply to A.C. circuit containing________?

Aresistance only

Binductance only

Ccapacitance only

Dall above

Correct answer

A. resistance only

Explanation

The correct answer is resistance only.

Time constant of a capacitive circuit________?

Aincreases with the decrease of capacitance and decrease of resistance

Bincrease with increase of capacitance and increase of resistance

Cincreases with the decrease of capacitance and increase of resistance

Dincreases with the increase of capacitance and decrease of resistance

Correct answer

B. increase with increase of capacitance and increase of resistance

Explanation

The correct answer is increase with increase of capacitance and increase of resistance.

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________?

Anone of the above

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

Cthe same heat as produced by A.C. when flowing through the same circuit

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

Correct answer

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

Explanation

The correct answer is the same heat as produced by A.C. when flowing through the same circuit.