Alternating Current Mock Test – Class 12 Physics

1. For a series circuit with and resonant frequency , the two half-power frequencies are symmetric approximately around . The approximate separation between them is

2. A circuit draws from a supply at power factor . The current component in phase with the voltage is

3. In a pure inductive circuit, the element that mainly opposes a change in current is

4. An ideal circuit has . If the maximum energy in the inductor is , the maximum current is

5. A resistor is connected to an supply of . The average power dissipated is

6. A damped oscillator shows decreasing peak charge on the capacitor. The best reason is that

7. A supply is marked , . Treating as the peak voltage would be unsuitable because practical voltage ratings usually give

8. Consider the following statements about an ideal transformer.
I. It changes voltage according to the turns ratio.
II. It changes the frequency of the supplied .
III. It transfers energy through changing magnetic flux.
IV. Its output power is equal to its input power.

9. In an ideal pure inductor, electrical energy supplied by the source is mainly

10. For a pure resistor, pure inductor, and pure capacitor, the opposition that is independent of frequency is

11. A series circuit has resonant frequency and quality factor . If the maximum power at resonance is , the approximate power at either half-power frequency is

12. In a pure resistor carrying sinusoidal , the instantaneous power is never negative because

13. A pure inductor has and is connected to an source with . The rms current is

14. For a pure resistive circuit, the set of suitable statements is:
I.
II. Voltage and current are in phase.
III. Average power over a cycle is zero.

15. A fixed pure inductor and a fixed pure capacitor have equal reactances at one frequency. If the frequency is increased, then

16. Assertion: The average value of a sinusoidal over a full cycle is zero.
Reason: The rms value of a sinusoidal is also zero over a full cycle.

17. The unit is most naturally associated with

18. In a pure inductive circuit, the voltage phasor is drawn ahead of the current phasor. If current is taken as the reference phasor, the voltage phasor is drawn

19. A sinusoidal alternating voltage has . Its mean value over the positive half cycle is approximately

20. A sinusoidal voltage is represented by a phasor of fixed length. If the convention says the phasor length represents peak value, then the length should be proportional to

21. An source is connected to a series circuit with , , and . The peak current is closest to

22. A transformer takes from the primary supply and delivers to the load. Its efficiency is

23. The same power is transmitted through wires of resistance first at voltage and then at voltage . If power factor effects are ignored, the line loss in the second case becomes

24. Use the arrangement described below.

The instantaneous current represented by this projection is

25. Use the graph description below.

This graph most directly represents

26. The unit of impedance in a series circuit is

27. A sinusoidal voltage has . Its peak voltage is approximately

28. For , , and in a series circuit, the impedance is

29. Use the graph description below.

The most suitable interpretation is that the capacitor

30. A sinusoidal current has zero mean over a full cycle. It can still heat a resistor because heating depends on

31. Use the graph description below.

Compared with graph P, graph Q has

32. Given , , and for a series circuit, its power factor is

33. At resonance, a series circuit with , , , and has the ratio

34. The quality factor of a series resonant circuit is related to resonant frequency and bandwidth by

35. A voltage waveform has maximum value and minimum value . Its peak-to-peak voltage is

36. For a circuit with , , and , the average power is

37. Assertion: A choke coil can reduce current without wasting as much power as a series resistor.
Reason: A choke coil uses inductive reactance, and its average power loss is small when its resistance is small.

38. Study the table and select the row that correctly compares a resistor and a choke coil used for reducing current.

39. A cell connected to a lamp gives a current in one fixed direction, while a mains supply drives current that reverses direction repeatedly. The mains supply is best described as

40. Taking , the resonant frequency of a series circuit with and is approximately

41. Match the quantities with their usual units.

42. A transformer is designed with . A load connected to the secondary receives in ideal operation. The primary current is

43. Consider the following statements about a non-zero sinusoidal alternating current.
I. Its full-cycle mean value is zero.
II. Its rms value is zero.
III. Its half-cycle mean value is .
IV. Its rms value is .

44. Use the arrangement described below.

If , the resultant source voltage lies

45. A record of an alternating voltage gives at one instant and . The best interpretation is that

46. A domestic supply value is commonly stated as . In elementary circuit calculations, this value normally refers to

47. Flux leakage in a transformer means that

48. A practical transformer is made with a laminated soft iron core and low-resistance copper windings. The most complete reason for these choices is to

49. A transformer works on the principle of

50. A practical transformer differs from an ideal transformer because practical transformers have