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Electrical Engineering
A.C Fundamentals, Circuits And Circuit Theory
Quiz 1
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Q.1
In a pure inductive circuit
The current is in phase with the voltage
The current lags behind the voltage by 90°
The current leads the voltage by 90°
The current can lead or lag by 90°
Q.2
In a pure resistive circuit
Current lags behind the voltage by 90°
Current leads the voltage by 90°
Current can lead or lag the voltage by 90°
Current is in phase with the voltage
Q.3
For a sine wave with peak value Emax ___________ 8.30. the average value is
0.636 Emax
0.707 Emax
0.434 EWc
lAUEmax
Q.4
The series and parallel resonance on L-C circuit' differs in that
Series resistance needs a low-resistance source for sharp rise in current
Series resonance needs a high-resistance source for sharp increase in current
Parallel resonance needs a low-resistance source for a sharp increase in impedance
Parallel resonance needs a low-resistance source for a sharp rise in line current
Q.5
At very low frequencies a series R-C circuit behaves as almost purely
Resistive
Inductive
Capacitive
None of the above
Q.6
In a series L-C circuit at the resonant frequency the
Current is maximum
Current is minimum
Impedance is maximum
Voltage across C is minimum
Q.7
In a circuit containing R, L and C, power loss can take place in
C only
L only
R only
All above
Q.8
Capacitors for power factor correction are rated in
kW
kVA
kV
kVAR
Q.9
The power consumed in a circuit element will be least when the phase difference between the current and voltage is
180°
90°
60°
0°
Q.10
Ohm is unit of all of the following except
Inductive reactance
Capacitive reactance
Resistance
Capacitance
Q.11
If resistance is 20 Q. and inductance is 27 in a R-L series circuit, then time constant of this circuit will be
0.001 s
0.1 s
10 s
100 s
Q.12
In a loss-free R-L-C circuit the transient current is
Oscillating
Square wave
Sinusoidal
Non-oscillating
Q.13
In an A.C. circuit power is dissipated in
Resistance only
Inductance only
Capacitance only
None of the above
Q.14
The input of an A.C. circuit having power factor of 0.8 lagging is 40 kVA
The power drawn by the circuit is
12 kW
22 kW
32 kW
64 kW
Q.15
The best place to install a capacitor is
Very near to inductive load
Across the terminals of the inductive load
Far away from the inductive load
Any where
Q.16
All definitions of power factor of a series R-L-C circuit are correct except
Ratio of net reactance and impedance
Ratio of kW and kVA
Ratio of J and Z
Ratio of W and VA
Q.17
The frequency of an alternating current is
The speed with which the alternator runs
The number of cycles generated in one minute
The number of waves passing through a point in one second
The number of electrons passing through a point in one second
Q.18
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,
The current through the resistance is more
The current through the resistance is less
Both resistance and inductance carry equal currents
None of the above
Q.19
Poor power factor
Reduces load handling capability of electrical system
Results in more power losses in the electrical system
Overloads alternators, transformers and distribution lines
Results in all above
Q.20
Which of the following statements pertains to resistors only?
Can dissipate considerable amount of power
Can act as energy storage devices
Connecting them in parallel increases the total value
Oppose sudden changes in voltage
Q.21
Wire-wound resistors are unsuitable for use at high frequencies because they
Create more electrical noise
Are likely to melt under excessive eddy current heat
Consume more power
Exhibit unwanted inductive and capacitive effects
Q.22
Form factor for a sine wave is
1.414
0.707
1.11
0.637
Q.23
The frequency of domestic power supply in India is
200 Hz
100 Hz
60 Hz
50 Hz
Q.24
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.
2.5
5
10
15
Q.25
Time constant of a circuit is the time in seconds taken after the application of voltage to each
25% of maximum value
50% of maximum value
63% of maximum value
90% of the maximum value
Q.26
Pure inductive circuit
Consumes some power on average
Does not take power at all from a line
Takes power from the line during some part of the cycle and then returns back to it during other part of the cycle
None of the above
Q.27
When an alternating current passes through an ohmic resistance the electrical power converted into heat is
Apparent power
True power
Reactive power
None of the above
Q.28
The r.m.s. value of a sinusoidal A.C. current is equal to its value at an angle of ________ degrees.
90
60
45
30
Q.29
The peak value of a sine wave is 200 V. Its average value is
127.4 V
141.4 V
282.8 V
200 V
Q.30
The product of apparent power and cosine of the phase angle between circuit voltage and current is
True power
Reactive power
Volt-amperes
Instantaneous power
0 h : 0 m : 1 s
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