Important MCQs of AC Circuits
In this post, some of the important mcqs of ac circuits are given. It includes emf equation of voltage, unit of frequency, definition of frequency, definition of time period, complex waveform, frequency of harmonics, reciprocal of time period and definition of cycle.
AC Circuit MCQs: 1 to 5
1 The emf equation of an alternating voltage is
( a )V = Vm sin ωt
( b )V = Vm tanωt
( c )V = Vmsin2ωt
( d )V = Vm2sin ωt
Correct Answer ( a ): V = Vm sin ωt
The standard equation of alternating emf is V = Vm sin ωt
V = Vm sin (2πf)t
V = Vm sin (2π/T)t ωt
V = Vm sin θ
2 The unit of frequency is
( a )Revolution / Second
( b )1 / Second
( c )Second
( d )Both ( a ) and ( b )
Correct Answer ( d ): Both ( a ) and ( b )
The unit of frequency is Hz of 1/Time.
3 The time taken by an alternating quantity to complete one cycle is called as
( a )Frequency
( b )Time period
( c )Cycle
( d )Amplitude
Correct Answer ( b ): Time period
Time period is defined as the time required for an alternating quantity to complete one cycle.
4 The number of cycles per second is called as
( a )Frequency
( b )Time period
( c )Cycle
( d )Any of the above
Correct Answer ( a ): Frequency
Frequency is defined as the number of cycle per second.
5 One complete cycle means
( a )π / 4 radian
( b )π / 2 radian
( c )π radian
( d )2π radian
Correct Answer ( d ): 2π radian
One cycle is equal to 2π radian or 360 degree, Half cycle is equal to π radian or 180 degree, One quarter cycle is equal to π/2 radian or 90 degree
AC Circuit MCQs: 6 to 10
6 The frequency of the alternating quantity is
( a )PN / 120
( b )PN / 60
( c )PN / 30
( d )120 / PN
Correct Answer ( a ): PN / 120
Frequency F = PN/120
Where P = Number of poles
N = Speed in RPM
7 Which of the following relation is true?
( a )T = f
( b )T = 1/f
( c )T = 1/f2
( d )None of the above
Correct Answer ( b ): T = 1/f
Time period = 1/ frequency
8 The time period for 50Hz cycle wave is
( a )0.1
( b )0.2
( c )0.02
( d )0.002
Correct Answer ( c ): 0.02
T = 1/f = 1/50 = 0.02 second
9 Which of the following relation is true?
( a )ω = 2πf
( b )ω = 2π / f
( c )ω = 2πT
( d )ω = f / 2π
Correct Answer ( a ): ω = 2πf
10 The complex waveform consists of
( a )Fundamental waveform
( b )Harmonics waveform
( c )Both ( a ) and ( b )
( d )None of the above
Correct Answer ( c ): Both ( a ) and ( b )
AC Circuit MCQs: 11 to 15
11 Which of the following is standard Indian fundamental frequency?
( a )25 Hz
( b )50 Hz
( c )100 Hz
( d )200 Hz
Correct Answer ( b ): 50 Hz
Frequency in Different Countries
12 If the fundamental frequency is 50Hz, the frequency of third harmonic is
( a )25 Hz
( b )50 Hz
( c )150 Hz
( d )250 Hz
Correct Answer ( c ): 150 Hz
The frequency of nth harmonic = nf
Where n = Harmonic Number
13 The two halves of complex waves are not identical when it consists of
( a )Fundamental component
( b )Odd harmonics component
( c )Even harmonics component
( d )Either ( b ) or ( c )
Correct Answer ( c ): Even harmonics component
14 Which of the following harmonics consists of distortion?
( a )3rd
( b )4th
( c )5th
( d )7th
Correct Answer ( b ): 4th
15 The reciprocal of the time period is called as
( a )Frequency
( b )Cycle
( c )Revolution
( d )Either ( a ) or ( b )
Correct Answer ( a ): Frequency
F = 1/T
AC Circuit MCQs: 16 to 20
16 The frequency of the 8 – pole, 50 Hz alternator is
( a )3000 RPM
( b )1500 RPM
( c )750 RPM
( d )600 RPM
Correct Answer ( c ): 750 RPM
Frequency F = PN/120
N = 120F / P = 120 × 50 / 8 = 750 RPM
17 One complete set of positive and negative value of alternating quantity is known as
( a )Frequency
( b )Cycle
( c )Time period
( d )Amplitude
Correct Answer ( b ): Cycle
One cycle is equal to one positive cycle and one negative cycle.
18 The maximum positive or negative value of alternating quantity is known as
( a )Form factor
( b )Peak factor
( c )Amplitude
( d )Either ( b ) or ( c )
Correct Answer ( c ): Amplitude
19 What is phase difference between following waveforms?
V1 = Vm sin ωt and V2 = Vm sin ( ωt – Фo )
( a )π / 2
( b )π
( c )Фo
( d )2Фo
Correct Answer ( c ): Фo
20 What is phase difference between following waveforms?
V1 = Vm sin ( ωt – 30o ) and V2 = Vm sin ( ωt – 90o )
( a )30o
( b )60o
( c )90o
( d )120o
Correct Answer ( b ): 60o
Phase difference is V1 is V2 with respect to X axis = – 30o + 90 o = 60 o
AC Circuit MCQs PDF
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