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%
Random questions: Yes
Certificate: Yes
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Progressive Test — Guest First Round

Alternating Current – Progressive Test

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1 / 50

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

a) the maximum value of voltage

b) phase difference

c) the unit of current

d) the resistance of a wire

2 / 50

2. The row that correctly compares average values of a sinusoidal quantity is

Row	Interval	Mean value of current
P	Full cycle
Q	Full cycle
R	Positive half cycle
S	Positive half cycle

a) Row P

b) Row R

c) Row Q

d) Row S

3 / 50

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

4 / 50

4. An ideal transformer steps down to . If the primary current is , the secondary current is

5 / 50

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

a) inductance becomes zero after the first oscillation

b) resistance dissipates energy as heat

c) capacitance changes sign every half cycle

d) energy conservation fails even in the ideal model

6 / 50

6. Assertion: In a series circuit, the average power is maximum when voltage and current are in phase.
Reason: The factor becomes when .

a) Assertion is true, but Reason is false

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

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

d) Assertion is false, but Reason is true

7 / 50

7. The capacitive reactance of a capacitor of capacitance at angular frequency is

8 / 50

8. A series resonant circuit has , , and resonant frequency . Taking , its bandwidth is closest to

9 / 50

9. A practical transformer has , , , and . Its efficiency is approximately

10 / 50

10. At resonance in a series circuit, the power factor is

11 / 50

11. 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) energy is stored and later returned

b) the current remains zero during the whole cycle

c) the voltage and current are in phase

d) the inductor permanently dissipates all supplied energy

12 / 50

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

13 / 50

13. A label on an source gives and . From these labels alone, the two reported quantities are

a) peak voltage and angular frequency

b) effective voltage and frequency

c) phase angle and peak current

d) instantaneous voltage and time period

14 / 50

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

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

b) equal primary and secondary turns in all cases

c) no magnetic flux in the core

d) winding resistance, flux leakage, and core losses

15 / 50

15. A pure resistor, pure inductor, and pure capacitor carry currents of the same . The one that certainly dissipates real average power in the ideal model is

a) pure inductor and pure capacitor only

b) pure inductor only

c) pure resistor only

d) pure capacitor only

16 / 50

16. The expression for a sinusoidal voltage refers to

a) average voltage over a full cycle

b) peak-to-peak voltage

c) rms voltage

d) average voltage over a half cycle

17 / 50

17. At very high frequency, the ideal element that tends to offer very small reactance is

a) a pure resistor with fixed

b) a pure capacitor

c) a real battery

d) a pure inductor

18 / 50

18. The equation of an alternating voltage is . The peak-to-peak separation on the voltage axis is

19 / 50

19. At resonance, a series circuit with , , , and has voltage across the capacitor

20 / 50

20. 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) half-power frequencies

b) zero-current frequencies

c) peak-current frequencies

d) equal-reactance frequencies

21 / 50

21. 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

a) opposite to current

b) behind current by

c) along the same direction as current

d) ahead of current by

22 / 50

22. 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 only

b) I, II, and III

c) I and II only

d) II and III only

23 / 50

23. An ideal capacitor is connected to an source with and . The average power consumed by the capacitor is

24 / 50

24. The magnetic energy stored in the inductor of an oscillator is

25 / 50

25. A heater coil has resistance and carries a sinusoidal current with . The average power developed in the coil is approximately

26 / 50

26. 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 true, but Reason is false

b) Assertion is false, but Reason is true

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

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

27 / 50

27. Use the arrangement described below.

In a series circuit phasor diagram, is drawn horizontally to the right. is drawn upward from the end of , and is drawn downward along the same vertical line.

If , the source voltage phasor lies

a) below the horizontal reference line

b) exactly along the horizontal line with no reactive component

c) opposite to the current phasor

d) above the horizontal reference line

28 / 50

28. With , , and in a series circuit, if the rms current is , the source voltage and average power are respectively

a) ,

b) ,

c) ,

d) ,

29 / 50

29. A resistor is connected to a sinusoidal voltage . The current through the resistor is

30 / 50

30. The current in an ideal pure inductor is called wattless mainly because

a) the rms current is always zero

b) the inductive reactance has no unit

c) current flows with zero cycle-average power

d) the voltage across the inductor is always zero

31 / 50

31. If the frequency of the applied is doubled for the same ideal inductor, the inductive reactance

a) becomes zero

b) becomes double

c) becomes half

d) remains unchanged

32 / 50

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

33 / 50

33. A pure inductor with is connected to a supply. Taking , its inductive reactance is approximately

34 / 50

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

35 / 50

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

a) is the peak voltage and is the instantaneous voltage

b) and must always be equal in an circuit

c) is the frequency of the supply

d) is the instantaneous voltage and is the peak voltage

36 / 50

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

37 / 50

37. When in a series circuit and , the source voltage at that frequency is

38 / 50

38. Use the graph description below.

Two sinusoidal graphs have the same time period. Graph P crosses zero with positive slope at . Graph Q crosses zero with positive slope at a later time.

The suitable conclusion is that

a) the two graphs must have zero amplitude

b) the two graphs must have different frequencies

c) Graph Q leads graph P

d) Graph Q lags graph P

39 / 50

39. The SI unit of capacitive reactance is

40 / 50

40. At a half-power frequency of a series circuit, the rms current is

a) zero

c) of the maximum current

d) equal to the maximum current

41 / 50

41. In a pure resistor connected to a sinusoidal source, voltage and current are

a) out of phase by , with current leading

b) always opposite in phase by

c) in phase

d) out of phase by , with current lagging

42 / 50

42. Use the graph description below.

Three opposition-frequency curves are drawn. Curve P is horizontal. Curve Q starts from zero and rises linearly with . Curve R is high at low and falls as increases.

The suitable identification is

a) P: , Q: , R:

b) P: , Q: , R:

c) P: , Q: , R:

d) P: , Q: , R:

43 / 50

43. 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) Kirchhoff’s voltage law fails in

c) the current through and must be zero

d) and are large but nearly opposite in phase

44 / 50

44. Use the graph description below.

Graph P shows and reaching maxima together. Graph Q shows reaching maximum one quarter cycle before . Graph R shows reaching maximum one quarter cycle before .

The suitable identification of P, Q, and R is

a) P: pure , Q: pure , R: pure

b) P: pure , Q: pure , R: pure

c) P: pure , Q: pure , R: pure

d) P: pure , Q: pure , R: pure

45 / 50

45. 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) four times the first value

b) half the first value

c) twice the first value

d) unchanged

46 / 50

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

47 / 50

47. Study the table and identify the suitable row about transformer losses and their reduction.

Row	Loss	Suitable reduction method
P	Eddy current loss	Use a laminated core
Q	Copper loss	Use very high-resistance winding wire
R	Hysteresis loss	Use a hard magnetic material with wide loop
S	Flux leakage	Remove the iron core completely

a) Row Q

b) Row S

c) Row R

d) Row P

48 / 50

48. 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) I, II, and III only

b) II and IV only

c) I, III, and IV only

d) I and II only

49 / 50

49. A graph is plotted with frequency on the horizontal axis and opposition on the vertical axis for ideal elements. The graph that is a horizontal line represents

a) inductive reactance

b) capacitive reactance

c) resistance

50 / 50

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

a) equal to

b) zero

c) equal to

d) maximum

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Alternating Current Mock Test – Class 12 Physics

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