MCQ on AC Circuits (Part-2)

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MCQ on AC Circuits

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MCQ on AC Circuits (Part-1)

Multiple Choice Questions

Q.1. A small capacitance is added to a highly inductive circuit,

  • the angle between voltage and current will increase
  • the pf will increase
  • the pf will decrease
  • the power drawn will decrease

Answer: the pf will increase

Q.2. In a series R-L-C circuit, R = 100 ohms, XL = 300 ohms and Xc = 200 ohms. The phase angle ϕ of the circuit is:

  • 0 degrees
  • 90 degrees
  • 45 degrees
  • -45 degrees

Answer: 45 degrees

Q.3. Under the condition of resonance in the RLC series circuit, the power factor of the circuit is

  • 0.5 lagging
  • 0.5 leading
  • unity
  • zero

Answer: unity

Q.4. When a sinusoidal voltage is applied across the R-L parallel circuit so that R = XL, the phase angle will be:

  • 45° lag
  • 45° leading
  • 90° lag
  • 90 leading

Answer: 45° leading

Q.5. The power factor of an inductive circuit is usually improved by adding a capacitor to it in:

  • series
  • parallel
  • either in series or parallel
  • none of these

Answer: either in series or parallel

Q.6. The operator j has a numerical value of

  • \sqrt{-1}
  • \sqrt{+1}
  • -1
  • 1

Answer: \sqrt{-1}

Q.7. The quantity (12 + j9) represents the resistive and reactive components of the current drawn by an ac circuit. The phase angle between the applied voltage and the current is:

  • 41.4°
  • 53.13°
  • 36.87°
  • 48.6°

Answer: 36.87°

Q.8. The Parallel R-C circuit behaves as a purely capacitive circuit at ………… frequencies.

  • very low
  • low
  • high
  • very high

Answer: very high

Q.9. The current read by the ammeter A in the ac circuit shown in the given figure is

  • 9 A
  • 5 A
  • 3 A
  • 1 A

Answer: 5 A

Q.10. Consider the following statements with respect to a series R-L-C circuit under resonance condition:

  1. All the applied voltage appears across R.
  2. There is no voltage across either L or C.
  3. The voltage across L and C equal and equal to their maximum values.

Of these statements

  • 1 alone is correct.
  • 2 alone is correct.
  • 1 and 3 are correct.
  • 1 and 2 are correct.

Answer: 1 alone is correct.

Q.11. In a series R-L-C circuit, the magnitude of resonance frequency can be changed by changing the value of

  • R only.
  • L only.
  • C only.
  • L or C.
  • R, L or C.

Answer: L or C

Q.12. A series-resonant circuit implies

  • zero pf and maximum current
  • unity pf and maximum current
  • unity pf and minimum current
  • zero pf and minimum current

Answer: unity pf and maximum current

Q.13. In an R-L-C parallel circuit, the line current at resonance is

  • minimum at unity power factor
  • minimum at lagging pf
  • maximum at leading pf
  • maximum at lagging pf

Answer: minimum at unity power factor

Q.14. The dynamic resistance of a parallel resonant circuit is given by

  • \frac{LC}{R_{L}}
  • LCR_{L}
  • \frac{C}{LR_{L}}
  • \frac{L}{CR_{L}}

Answer: \frac{L}{CR_{L}}

Q.15. A parallel resonant circuit can be employed

  • as a high impedance
  • to reject a small band of frequencies
  • to amplify certain frequencies
  • to amplify voltage
  • both high impedance and reject a small band of frequencies

Answer: both high impedance and reject a small band of frequencies

Q.16. In a 3-phase system, the EMFs are

  • 30° apart
  • 40° apart
  • 90° apart
  • 120° apart

Answer: 120° apart

Q.17. The relationship between the line and phase voltage of a delta-connected circuit is given by

  • V_{L}=V_{P}
  • V_{L}=\sqrt{3}V_{P}
  • V_{L}=\frac{V_{P}}{\sqrt{2}}
  • V_{L}=\frac{2}{\Pi }V_{P}

Answer: V_{L}=V_{P}

Q.18. In the case of a delta connected load, if one resistor is removed, the power will become

  • zero
  • one-third
  • two-third
  • none of these

Answer: two-third

Q.19. A 3-phase 6.6/0.4 kV transformer is to supply a load at 230 V. Its secondary should be connected in

  • star
  • delta
  • open-delta
  • series
  • parallel

Answer:  star

Q.20. In the balanced 3-phase voltage system generated by a star connected alternator, VYB lags ER by

  • 90 degrees
  • 120 degrees
  • 60 degrees
  • 30 degrees

Answer: 90 degrees

Q.21. A 3-phase, star-connected symmetrical load consumes P watts of power from a balanced supply. If the same load is connected in delta to the same supply, the power consumption will be

  • P
  • \sqrt{3}P
  • 3P
  • P/3

Answer: 3P

Q.22. In the 2 WM method of power measurement, one of the W.M. will show negative reading when the load pf angle is strictly

  • less than 30°
  • less than 60°
  • greater than 30°
  • greater than 60°

Answer: greater than 60°

Q.23. While measuring power in a three-phase load by 2 WM method. The reading of two wattmeters are equal and opposite, when

  • pf is unity
  • load is balanced
  • phase angle is between 60° and 30°
  • the load is purely inductive

Answer: the load is purely inductive

Q.24. A lamp load is given a supply from 3-phase, 4-wire 230/400 V, A.C. supply system. If a 3- phase motor is now switched on across the same supply, then neutral current will

  • increase
  • decrease
  • remain unchanged
  • be unpredictable

Answer: decrease

Q.25. A set of 3 equal resistors, each of value Rx connected in star across RYB in place of load as shown in the given figure consumes the same power as the unbalanced delta connected load. The value of Rx is

  • 33.33 Ω
  • 100 Ω
  • 173.2 Ω
  • 300 Ω   

Answer: 100 Ω

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