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
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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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Alternating Current – Progressive Test

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1 / 50

1. For in a series circuit, the current

a) is always in phase with source voltage

b) becomes zero at every instant

c) lags the source voltage

d) leads the source voltage

2 / 50

2. In an ideal transformer, the voltage ratio is related to the turns ratio by

3 / 50

3. A fixed , fixed , and fixed are separately connected to the same sinusoidal source. The frequency is increased while is kept constant. The current through , , and respectively

a) remains unchanged, decreases, increases

b) remains unchanged, increases, decreases

c) decreases, remains unchanged, increases

d) increases, decreases, remains unchanged

4 / 50

4. Two alternating quantities are said to be in phase when they

a) reach corresponding values together

b) always have different signs

c) have different frequencies but equal peak values

d) differ in phase by

5 / 50

5. A capacitor of capacitance is connected to an source with . Its capacitive reactance is

6 / 50

6. A pure capacitor has and . The peak current and phase relation are

a) , current leads voltage by

b) , current leads voltage by

c) , current lags voltage by

d) , voltage leads current by

7 / 50

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

8 / 50

8. The phase angle in elementary notation is used to describe

a) the unit of current

b) phase difference

c) the resistance of a wire

d) the maximum value of voltage

9 / 50

9. 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 .

a) II and IV only

b) I, II, and III only

c) I, III, and IV only

d) I and II only

10 / 50

10. A sinusoidal voltage has . Its angular frequency is

11 / 50

11. Study the table and identify the suitable row for a pure inductive circuit.

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

a) Row Q

b) Row S

c) Row R

d) Row P

12 / 50

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

a) the equal-heating current

b) the algebraic average of current over one full cycle

c) the current value exactly at every zero crossing

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

13 / 50

13. The phase angle in a series circuit is given by

14 / 50

14. The SI unit of inductive reactance is

15 / 50

15. In one complete cycle of a sinusoidal alternating voltage, the phase angle changes by

16 / 50

16. 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.

a) I, II, and III only

b) II and IV only

c) I, II, III, and IV

d) I, III, and IV only

17 / 50

17. A pure resistor, pure inductor, and pure capacitor are compared at the same . Their average powers in the ideal model are respectively

a) zero, zero, non-zero

b) zero, non-zero, zero

c) non-zero, zero, zero

d) non-zero, non-zero, non-zero

18 / 50

18. In an ideal pure capacitor connected to a sinusoidal voltage, the current

a) is always in phase with voltage

b) leads voltage by

c) lags voltage by

d) is opposite in phase to voltage by

19 / 50

19. For two sinusoidal quantities of the same frequency, a time difference corresponds to a phase difference

20 / 50

20. In a series circuit, increasing the frequency from well below resonance to well above resonance changes the circuit nature in the order

a) capacitive inductive resistive

b) resistive capacitive inductive

c) capacitive resistive at resonance inductive

d) inductive resistive at resonance capacitive

21 / 50

21. If the frequency of an alternating current is doubled, while the waveform remains sinusoidal, its time period

a) becomes double

b) becomes zero

c) remains unchanged

d) becomes half

22 / 50

22. In a series circuit with , , and , the value of is

23 / 50

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

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

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

c) Assertion is false, but Reason is true

d) Assertion is true, but Reason is false

24 / 50

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

a) no magnetic flux in the core

b) winding resistance, flux leakage, and core losses

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

d) equal primary and secondary turns in all cases

25 / 50

25. Study the table and identify the row that correctly describes resonance sharpness.

Row	Condition	Resonance feature
P	Large	Narrow bandwidth and high selectivity
Q	Large	Wide bandwidth and low selectivity
R	Small	Small
S	Large	Always sharper resonance

a) Row S

b) Row P

c) Row R

d) Row Q

26 / 50

26. Match the transformer quantities and relations.

Column I	Column II
P. Voltage ratio	1.
Q. Current ratio	2.
R. Ideal power relation	3.
S. Efficiency	4.

a) P-1, Q-2, R-3, S-4

b) P-4, Q-2, R-1, S-3

c) P-1, Q-3, R-2, S-4

d) P-2, Q-1, R-3, S-4

27 / 50

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

28 / 50

28. A sinusoidal current lags a voltage by . If the voltage is written as , a suitable current expression is

29 / 50

29. For a series circuit with , , and , the rms source voltage is

30 / 50

30. A practical transformer has input power and efficiency . The power lost inside the transformer is

31 / 50

31. A small resistance is introduced into an oscillator. The most suitable effect is that the oscillations become

a) undamped with constant amplitude forever

b) damped by energy loss as heat

c) faster with infinite frequency

d) impossible because current cannot flow through an inductor

32 / 50

32. A table lists two dimensionless ratios for a sinusoidal waveform.

Row	Ratio	Value
P
Q
R

For a non-zero sinusoidal , the suitable rows are

a) Q and R only

b) P and Q only

c) P and R only

d) P, Q, and R

33 / 50

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

34 / 50

34. A table compares two devices used with .

Row	Device	Main useful action	Key condition
P	Choke coil	Limits current with small real power loss	High , low
Q	Transformer	Changes voltage level by mutual induction	Changing magnetic flux
R	Choke coil	Steps up voltage by turns ratio
S	Transformer	Works continuously on steady	Constant flux

The fully suitable rows are

a) P, Q, R, and S

b) P and Q only

c) P and S only

d) Q and R only

35 / 50

35. Study the table and identify the row that correctly represents power in a series circuit.

Row	Quantity	Suitable expression
P	Average power
Q	Power factor
R	Real power
S	Apparent power

a) Row R

b) Row P

c) Row Q

d) Row S

36 / 50

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

37 / 50

37. A phasor representation of a sinusoidal quantity uses a rotating vector whose projection gives

a) the full-cycle mean value only

b) the number of turns in a transformer

c) the resistance of the circuit only

d) the instantaneous sinusoidal value

38 / 50

38. Real average power in a series circuit is associated with

a) the resistive part of the circuit

b) the arithmetic sum alone

c) the inductive reactance alone

d) the capacitive reactance alone

39 / 50

39. For in a series circuit, the circuit behaves as

a) an open circuit with zero current always

b) purely resistive at all frequencies

c) inductive, with current lagging voltage

d) capacitive, with current leading voltage

40 / 50

40. A sinusoidal current has peak value , instantaneous value , and rms value . At different instants in a cycle, may be

a) always numerically larger than

b) only equal to

c) positive, zero, or negative

d) only equal to

41 / 50

41. Assertion: If the frequency of an alternating current increases, the time period decreases.
Reason: Frequency and time period satisfy .

a) Assertion is false, but Reason is true

b) Assertion is true, but Reason is false

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

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

42 / 50

42. The row that correctly distinguishes mean value and rms value for sinusoidal is

Row	Quantity	Correct interpretation
P	Full-cycle mean	Always equal to
Q		Effective value based on heating effect
R	Half-cycle mean
S		Algebraic average over one complete cycle

a) Row R

b) Row S

c) Row Q

d) Row P

43 / 50

43. A transformer delivers at to a load and has efficiency . If the primary voltage is , the primary current is

44 / 50

44. A voltage is described by . The same source is observed after half a cycle from an instant when the voltage was . The voltage then becomes

45 / 50

45. In an circuit, is called apparent power, while is real average power. The two are equal only when

46 / 50

46. The statement for a sinusoidal voltage means that

a) the rms voltage is greater than the peak voltage

b) the rms voltage is the full-cycle mean voltage

c) the rms voltage is about

d) the peak voltage is half of the rms voltage

47 / 50

47. Use the arrangement described below.

In a series circuit, current is taken along the horizontal reference line. The resistor voltage is drawn along this same line. The inductor voltage is drawn upward, and the capacitor voltage is drawn downward.

If , the resultant source voltage lies

a) along the horizontal line only

b) below the horizontal reference line

c) opposite to the resistor voltage

d) above the horizontal reference line

48 / 50

48. For a sinusoidal alternating current with peak value , the rms value is

49 / 50

49. A sinusoidal current has . Its mean value over a half cycle is approximately

50 / 50

50. A pure inductor has and . The peak current and phase relation are

a) , current lags voltage by

b) , current leads voltage by

c) , voltage lags current by

d) , current lags voltage by

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Alternating Current Mock Test – Class 12 Physics

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