## MCQ on AC Circuits

MCQ on AC Circuits, Alternating Current MCQ, MCQ on Alternating Current, Multiple Choice Questions on MCQ on AC Circuits, Engineering MCQ, Basic Electrical Engineering MCQ

### 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, X_{L} = 300 ohms and X_{c} = 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 = X_{L}, 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:

- All the applied voltage appears across R.
- There is no voltage across either L or C.
- 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, V_{YB} lags E_{R} 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 R_{x} connected in star across R_{YB} in place of load as shown in the given figure consumes the same power as the unbalanced delta connected load. The value of R_{x} is

- 33.33 Ω
- 100 Ω
- 173.2 Ω
- 300 Ω

**Answer:** 100 Ω