Alternating Current Mock Test

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Quiz: Alternating Current – Progressive Test
Total questions: 400
Questions in this round: 50
Time allotted: 70 minutes
Pass score: 60%
Total rounds: 8
Current round: 1^st
Rounds passed: 0 / 8
Weakest rounds: None
Rounds attempted: 0

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Quiz: Alternating Current – Certificate Challenge
Total questions: 400
Questions to attempt: 100 random
Time allotted: 100 minutes
Certificate pass score: 70%
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Certificate: Yes
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Progressive Test — Guest First Round

Alternating Current – Progressive Test

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1 / 50

1. A current through an ideal inductor is momentarily constant. At that instant, the magnitude of is

a) equal to

b) zero

c) maximum

d) equal to

2 / 50

2. For in a series circuit, the current

a) is always in phase with source voltage

b) becomes zero at every instant

c) leads the source voltage

d) lags the source voltage

3 / 50

3. Use the graph description below.

For a pure inductor, the instantaneous power-time graph has equal positive and negative regions over one complete cycle.

The physical meaning of this graph is that

a) the current remains zero during the whole cycle

b) the voltage and current are in phase

c) energy is stored and later returned

d) the inductor permanently dissipates all supplied energy

4 / 50

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

a) and must always be equal in an circuit

b) is the frequency of the supply

c) is the instantaneous voltage and is the peak voltage

d) is the peak voltage and is the instantaneous voltage

5 / 50

5. If the voltage across a pure inductor is , a suitable expression for the current is

6 / 50

6. A resistor is supplied with and carries . Its resistance is

7 / 50

7. A pure resistor of resistance is connected to an source with . The peak current is

8 / 50

8. A load takes the same real power from an supply at two different power factors. If is fixed, a lower power factor requires

a) no change in current under any condition

b) zero current for the same real power

c) larger current for the same real power

d) smaller current for the same real power

9 / 50

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

10 / 50

10. The angular frequency of an alternating quantity is related to frequency by

11 / 50

11. Series resonance in an circuit occurs when

12 / 50

12. Use the graph description below.

For a series circuit, an -frequency graph has a maximum current at the resonant frequency . At two frequencies on either side of , the current becomes .

The two side frequencies are called

a) equal-reactance frequencies

b) zero-current frequencies

c) peak-current frequencies

d) half-power frequencies

13 / 50

13. Given , , and for a series circuit, the inductance is

14 / 50

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

15 / 50

15. A tuning circuit based on series resonance has and . Its bandwidth is

16 / 50

16. 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

c) only

17 / 50

17. The peak factor for a sinusoidal alternating current is defined as . Its value is

18 / 50

18. Read the passage and answer the question.

An alternating current is described by . During one interval, the sine factor is positive. During the next equal interval, the sine factor is negative.

What changes between these two intervals?

a) The amplitude becomes zero

b) The unit of current changes

c) The chosen reference direction disappears

d) The current direction reverses

19 / 50

19. The root mean square value of an alternating current is best understood as

a) the current value exactly at every zero crossing

b) the equal-heating current

c) the maximum value reached by current in the positive half cycle

d) the algebraic average of current over one full cycle

20 / 50

20. At the instant when the capacitor charge is maximum in an ideal oscillator, the current in the inductor is

a) equal to at all such instants

b) zero

c) equal to

d) maximum

21 / 50

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

22 / 50

22. A pure inductor is connected first to and then to , with the same rms voltage in both cases. The rms current in the second case becomes

a) unchanged

b) half the first value

c) four times the first value

d) twice the first value

23 / 50

23. 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

a) , because its voltage can have a fixed rating

b) , because the current direction reverses periodically

c) , because it can operate a lamp

d) , because every household device must contain a capacitor

24 / 50

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

25 / 50

25. Assertion: An ideal pure capacitor consumes zero average power in sinusoidal steady-state .
Reason: In a pure capacitor, current leads voltage by .

a) Assertion is false, but Reason is true

b) Assertion is true, but Reason is false

c) Both Assertion and Reason are true, but Reason does not explain Assertion

d) Both Assertion and Reason are true, and Reason explains Assertion

26 / 50

26. A choke coil has high inductance and very small resistance. When connected to , its power factor is expected to be

a) greater than

b) close to

c) close to

d) exactly equal to

27 / 50

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

a) capacitance changes sign every half cycle

b) resistance dissipates energy as heat

c) energy conservation fails even in the ideal model

d) inductance becomes zero after the first oscillation

28 / 50

28. Use the graph description below.

A graph of current against time is a smooth wave. It rises to a positive maximum, returns to zero, reaches an equal negative maximum, and then returns to zero again in a repeating pattern.

This graph most directly represents

a) a current with no direction reversal

b) zero current at all instants

c) sinusoidal

d) steady

29 / 50

29. For a pure capacitor, and . The instantaneous power changes sign during a cycle because

a) the rms voltage changes sign every half cycle

b) phase difference is

c) capacitance becomes zero during the negative half cycle

d) voltage and current are always in phase

30 / 50

30. In a series circuit, the source voltage is , the current is , and the average power is . The power factor is

31 / 50

31. A circuit is to select one radio-frequency signal from many nearby signals. The desirable resonance curve should be

a) narrow and sharply peaked

b) highest at zero frequency only

c) broad and flat

d) horizontal for all frequencies

32 / 50

32. Read the passage and answer the question.

A transformer has and . The primary is connected to a alternating supply. Losses are neglected.

The secondary voltage is closest to

33 / 50

33. Use the energy description below.

In an ideal circuit, Stage P has maximum charge on the capacitor and zero current. Stage Q has zero charge on the capacitor and maximum current through the inductor.

The suitable energy identification is

a) Stage P and Stage Q: only heat energy is present

b) Stage P: magnetic energy maximum; Stage Q: electric energy maximum

c) Stage P and Stage Q: both energies zero

d) Stage P: electric energy maximum; Stage Q: magnetic energy maximum

34 / 50

34. The notation is used instead of in an equation when the voltage value is meant to be

a) instantaneous voltage

b) the time period of the supply

c) the maximum voltage only

d) the number of cycles per second

35 / 50

35. An ideal circuit has and . Its angular frequency of oscillation is

36 / 50

36. The inductive reactance of an inductor of inductance at angular frequency is

37 / 50

37. An electric current is called alternating current when it

a) flows only in one direction with constant magnitude

b) exists only in a circuit containing a capacitor

c) changes only its magnitude but never reverses direction

d) changes magnitude and direction periodically

38 / 50

38. Study the table and identify the suitable row for a pure capacitive circuit.

Row	Feature	Pure capacitor result
P	Phase relation	Current leads voltage by
Q	Reactance
R	Frequency effect	increases as increases
S	Average power	Always equal to

a) Row Q

b) Row S

c) Row R

d) Row P

39 / 50

39. A meter method averages the signed value of a pure sinusoidal current over a full cycle. The reading expected from this averaging alone is

40 / 50

40. At very low frequency approaching steady , the ideal element that tends to offer very large reactance is

a) a short copper wire only

b) a pure inductor

c) a pure capacitor

d) a pure resistor

41 / 50

41. At a half-power frequency of a series circuit, and . The rms current and average power at that frequency are

a) ,

b) ,

c) ,

d) ,

42 / 50

42. For a series resonant circuit, if the half-power frequencies are and , the bandwidth is

43 / 50

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

44 / 50

44. A waveform is described by the readings , , , , and in sequence over one cycle. The value that changes from instant to instant is

45 / 50

45. A data sheet lists a current as . The statement means that

a) the current is at every instant

b) the phase angle is

c) the time period is

d) the peak current is

46 / 50

46. Near resonance in a series circuit, high voltages may appear across and even when the source voltage is modest. The safest interpretation is that

a) the resistor voltage is always greater than both and

b) and are large but nearly opposite in phase

c) the current through and must be zero

d) Kirchhoff’s voltage law fails in

47 / 50

47. 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.

a) I and II only

b) I, II, and III

c) I only

d) II and III only

48 / 50

48. A sinusoidal voltage has . Its angular frequency is

49 / 50

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

a) no winding resistance, no flux leakage, and no core loss

b) winding resistance, flux leakage, and core losses

c) no magnetic flux in the core

d) equal primary and secondary turns in all cases

50 / 50

50. A transformer core is laminated into thin insulated sheets. This construction mainly reduces heating caused by

a) direct current flowing through the dielectric

b) resistance of the external load only

c) absence of magnetic flux in the secondary coil

d) circulating currents induced inside the core

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Alternating Current Mock Test – Class 12 Physics

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