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MCQ on AC Circuits

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1. A current is said to be direct current when its




2. A current is said to be alternating when it changes in




3. The standard supply frequency in India is




4. The angular frequency of an alternating quantity is a mathematical quantity obtained by multiplying the frequency f of the alternating quantity by a factor




5. A constant current of 2.8 A exists in a resistor. The RMS value of current is




6. The ratio of effective value to average value is called the …. factor.




7. The RMS value of a sine wave is 100 A. Its peak value is




8. When the two quantities are in quadrature the phase angle between them will be




9. In ac circuits the power curve is a sine wave having




10. Electrical power converted into heat due to the flow of an alternating current through an ohmic resistance is called the …….. power.




11. Average power in a purely resistive circuit is equal to




12. If an alternating triangular voltage is applied to a resistor, the shape of the current waveform will be ……. waveform.




13. The purely inductive circuit takes power from the ac mains when




14. Which of the following statements associated with a purely capacitive circuit is not true?




15. A two-terminal black box contains a series combination of a resistor and an unknown two-terminal linear device. As soon as the battery is connected to the black box the current is found to be zero. The device is




16. The reactance offered by a capacitor to alternating current of frequency 50 Hz is 10 Ω. If the frequency is increased to 100 Hz, reactance becomes:




17. The apparent power and active power is drawn are equal for an ac circuit of:




18. When a sinusoidal voltage is applied across R-L series circuit having R = XL, the phase angle will be:




19. In a series R-L circuit




20. In an ac circuit, the applied voltage and current drawn are represented as v = Vmax sin ωt and i = Imax sin (ωt + ϕ). The pf of the circuit is




21. Q-factor of a coil is the measure of its




22. In a series R-C circuit current …….. with the increase in frequency.




23. A 100 W, 100 V bulb is to be supplied from 220 V, 50 Hz supply. Which of the following arrangements is preferable?




24. The source in the circuit shown is a sinusoidal source. The supply voltage across various elements is marked in the figure. The input voltage is




25. If a series RLC circuit is excited by a voltage e = E sin ωt where LC < 1/ω2




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




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




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




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




30. 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:




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




32. 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




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




34. A series-resonant circuit implies




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




36. A parallel resonant circuit can be employed




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




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




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




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




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




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




43. 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