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. Use the graph description below.

A graph shows rising linearly with frequency and falling with frequency. The two curves cross at one point.

For a series circuit containing the same and , the crossing point represents

a) maximum capacitive reactance only

b) resonance where

c) the condition where current must be zero

d) zero inductance and zero capacitance

2 / 50

2. 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 peak current is

d) the time period is

3 / 50

3. An alternating voltage has frequency . The time taken for one half cycle is

4 / 50

4. 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

5 / 50

5. Given a series circuit with , , and , its impedance is

6 / 50

6. Study the table and identify the row that correctly links net reactance and circuit nature in a series circuit.

Row	Circuit nature	Current behaviour
P	Inductive	Current lags voltage
Q	Inductive	Current lags voltage
R	Capacitive	Current leads voltage
S	Capacitive	Current leads voltage

a) Row P

b) Row S

c) Row R

d) Row Q

7 / 50

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

8 / 50

8. The frequency dependence means that an ideal capacitor offers

a) greater opposition at higher frequency

b) opposition independent of frequency

c) less opposition at higher frequency

d) zero opposition only at

9 / 50

9. The unit is most naturally associated with

a) rms current

b) peak voltage

c) angular frequency

d) time period

10 / 50

10. 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

b) capacitive reactance

c) resistance

d) inductive reactance

11 / 50

11. A series circuit has , , , and . At , the rms current and circuit nature are closest to

a) , inductive

b) , capacitive

c) , capacitive

d) , inductive

12 / 50

12. With current as the reference phasor in a pure capacitive circuit, the voltage phasor should be drawn

a) along the same direction as current

b) opposite to current by

c) behind the current phasor

d) ahead of the current phasor

13 / 50

13. In a power distribution system, a step-down transformer is used near consumers mainly to

a) convert the transformer core into a permanent magnet

b) increase voltage to a very high value for household appliances

c) stop mutual induction completely

d) reduce voltage to a safer and usable level

14 / 50

14. A fixed capacitor is connected to and then to , with the same in both cases. The second rms current is

a) twice the first rms current

b) half the first rms current

c) one fourth of the first rms current

d) equal to the first rms current

15 / 50

15. A series resonant circuit has and bandwidth . Its quality factor is

16 / 50

16. A claim says: “If and , the source must supply at least .” The claim is unsuitable because

a) inductor voltage is not measured in volts

b) series current cannot pass through a capacitor

c) and are in opposite phasor directions

d) capacitor voltage is always zero in

17 / 50

17. If , the correct statement for ideal transformer operation is that it

a) works only with steady

b) steps up voltage and steps down current

c) steps down both voltage and current without changing power

d) steps down voltage and steps up current

18 / 50

18. Use the graph description below.

Two sinusoidal voltage graphs have the same time period. Graph P reaches and . Graph Q reaches and .

Compared with graph P, graph Q has

a) half the peak voltage and double the frequency

b) double the rms value only if its time period is also doubled

c) double the peak voltage and the same frequency

d) the same peak voltage and half the frequency

19 / 50

19. A resistor is connected first to a current and then to a sinusoidal current with . For equal time intervals, the heat produced in the resistor is

a) greater with only

b) greater with only

c) the same in both cases

d) zero with because its mean current is zero

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 resistive at resonance inductive

b) capacitive inductive resistive

c) resistive capacitive inductive

d) inductive resistive at resonance capacitive

21 / 50

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

22 / 50

22. A changing primary current in a transformer produces a secondary emf of the same frequency mainly because

a) the secondary coil is connected directly to the primary wire

b) the same changing flux links both coils

c) the number of secondary turns must equal the number of primary turns

d) the iron core acts as a battery

23 / 50

23. The magnitude form of the voltage-current relation for an ideal inductor in analysis is

24 / 50

24. 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.

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

25 / 50

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

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

b) the algebraic average of current over one full cycle

c) the equal-heating current

d) the current value exactly at every zero crossing

26 / 50

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

a) , current leads voltage by

b) , voltage leads current by

c) , current leads voltage by

d) , current lags voltage by

27 / 50

27. A statement about a pure capacitor says: “Since the average power is zero, the capacitor has no energy at any instant.” This statement is unsuitable because

a) a capacitor can store only magnetic field energy

b) temporary electric-field storage can occur

c) zero average power means zero instantaneous energy at all times

d) current and voltage are always in phase in a capacitor

28 / 50

28. At resonance, a series circuit with and has rms current

29 / 50

29. A transformer supplies at on the secondary side. If it is ideal and the primary voltage is , the primary current is

30 / 50

30. A sinusoidal voltage has the same heating effect in a given resistor as a source. The rms voltage of the source is

31 / 50

31. A phasor diagram is drawn using rms convention instead of peak convention. For a sinusoidal voltage with , the voltage phasor length should be

32 / 50

32. With current as the horizontal reference in a series circuit, , , and are drawn respectively as

a) downward, upward, horizontal

b) horizontal, downward, upward

c) horizontal, upward, downward

d) upward, horizontal, downward

33 / 50

33. 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) peak-current frequencies

c) equal-reactance frequencies

d) zero-current frequencies

34 / 50

34. In a series phasor diagram, current is commonly chosen as the reference because

a) the capacitor voltage is always equal to the resistor voltage

b) the source voltage is always zero

c) current is different in the three elements

d) the same current flows through , , and

35 / 50

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

36 / 50

36. The opposite directions of and in a series phasor diagram occur because

a) the same current cannot pass through both and

b) the resistor voltage cancels both of them

c) the inductor and capacitor always have equal voltages

d) leads current and lags current

37 / 50

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

a) a real battery

b) a pure inductor

c) a pure capacitor

d) a pure resistor with fixed

38 / 50

38. The time period of an alternating quantity describes

a) the maximum value reached by current

b) the time taken to complete one full cycle

c) the heating-equivalent value of voltage

d) the angle between voltage and current phasors only

39 / 50

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

a) undamped with constant amplitude forever

b) impossible because current cannot flow through an inductor

c) faster with infinite frequency

d) damped by energy loss as heat

40 / 50

40. For , the voltage has its negative peak when

d) only

41 / 50

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

a) remains unchanged

b) becomes double

c) becomes half

d) becomes zero

42 / 50

42. Use the graph description below.

A voltage-time graph and a current-time graph for a circuit cross zero together, reach positive maxima together, and reach negative maxima together.

The circuit behaviour most directly shown by these two graphs is

a) transformer action

b) pure resistive behaviour

c) pure inductive behaviour

d) pure capacitive behaviour

43 / 50

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

44 / 50

44. The SI unit of inductive reactance is

45 / 50

45. A sinusoidal alternating current is given by . In this equation, the factor that sets the largest possible magnitude of current is

46 / 50

46. A series circuit starts at resonance. The supply frequency is then increased slightly while , , , and remain fixed. The current and circuit nature change as

a) current decreases and the circuit becomes inductive

b) current increases and the circuit becomes capacitive

c) current remains maximum and the circuit stays purely resistive

d) current becomes zero and the circuit becomes a transformer

47 / 50

47. 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, III, and IV

b) I, III, and IV only

c) I, II, and III only

d) II and IV only

48 / 50

48. A pure capacitor has and is connected to a source with . The rms current is

49 / 50

49. Consider the following statements about phase difference in .
I. Phase difference may be expressed in radians.
II. A phase difference of means the two quantities are in phase.
III. If current leads voltage, current reaches corresponding maxima earlier than voltage.

a) I and III only

b) I, II, and III

c) II and III only

d) I and II only

50 / 50

50. Given , , and in a series circuit, the rms source voltage is

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Alternating Current Mock Test – Class 12 Physics

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Alternating Current – Progressive Test

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