Circuits and Circuit Theory

71.The inductance of a coil can be increased by

1. increasing core length
2. decreasing the number of turns
3. decreasing the diameter of the former
4. choosing core material having high relative permeability

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72.The input of an A.C. circuit having power factor of 0.8 lagging is 40 kVA The power drawn by the circuit is

1. 12 kW
2. 22 kW
3. 32 kW
4. 64 kW

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73.The peak value of a sine wave is 200 V. Its average value is

1. 127.4 V
2. 141.4 V
3. 282.8 V
4. 200V

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74.The period of a sine wave is _________ seconds. Its frequency is

1. 20 Hz
2. 30 Hz
3. 40 Hz
4. 50 Hz

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75.The period of a wave is

1. the same as frequency
2. time required to complete one cycle
3. expressed in amperes
4. none of the above

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

1. both waves must have same frequency
2. both waves must have identical peak values
3. both waves must have zero value at the same time
4. none of the above

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77.The phosphors for which of the following pair are 180° out of phase for VL, VC and VR?

1. Vc and VR
2. VL and VR
3. Vc and VL
4. none of the above

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78.The power consumed in a circuit element will be least when the phase difference between the current and voltage is

1. 180"
2. 90°
3. 60°
4. 0°

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

1. zero
2. 0.08 lagging
3. 0.8 leading
4. unity

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80.The power factor of a D.C. circuit is always

1. less than unity
2. unity
3. greater than unity
4. zero

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