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

a) the instantaneous sinusoidal value

b) the number of turns in a transformer

c) the full-cycle mean value only

d) the resistance of the circuit only

2 / 50

2. Two sinusoidal currents are represented by and . The two currents have the same

a) unit of voltage

b) instantaneous value at every instant only

c) peak value only

d) angular frequency and phase pattern

3 / 50

3. 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 remains maximum and the circuit stays purely resistive

b) current becomes zero and the circuit becomes a transformer

c) current decreases and the circuit becomes inductive

d) current increases and the circuit becomes capacitive

4 / 50

4. 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) zero-current frequencies

d) equal-reactance frequencies

5 / 50

5. In ideal transformer operation, . The relation between secondary and primary currents is

6 / 50

6. The row that correctly identifies a transformer feature and its effect is

Row	Feature	Effect
P	Step-up transformer	Raises voltage and lowers current for the same ideal power
Q	Laminated core	Increases eddy current heating
R	Soft iron core	Prevents any flux linkage with the secondary
S	Low-resistance windings	Increase copper loss deliberately

a) Row P

b) Row R

c) Row Q

d) Row S

7 / 50

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

8 / 50

8. In , the argument must represent an angle. This is consistent because

a) is a current and must be measured in

b) has unit

c) both and are measured in

d) has unit and has unit

9 / 50

9. The opposition offered by an ideal inductor to sinusoidal is called

a) resistance

b) conductance

c) capacitive reactance

d) inductive reactance

10 / 50

10. For the equation , the voltage is zero whenever

11 / 50

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

a) zero current for the same real power

b) larger current for the same real power

c) no change in current under any condition

d) smaller current for the same real power

12 / 50

12. A tuning circuit with very high is not always desirable for receiving a signal with a range of useful side frequencies because

a) high removes the capacitor from the circuit

b) high changes the signal into steady

c) high makes the response very narrow

d) high makes the resistance infinite in all cases

13 / 50

13. If a series circuit has and impedance , the rms current is

14 / 50

14. A voltage is written as . At the instant when , the voltage is

15 / 50

15. 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 voltage and current are in phase

c) the current remains zero during the whole cycle

d) the inductor permanently dissipates all supplied energy

16 / 50

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

a) close to

b) greater than

c) exactly equal to

d) close to

17 / 50

17. A claim says: “The rms value of an voltage is the same as the voltage at every instant.” This claim is

a) unsuitable, because rms values are used only for

b) suitable, because is another name for

c) suitable, because voltage has no peak value

d) unsuitable; varies with time

18 / 50

18. A series circuit has maximum current at resonance. At a half-power frequency, the current is closest to

19 / 50

19. An electric current is called alternating current when it

a) flows only in one direction with constant magnitude

b) changes only its magnitude but never reverses direction

c) exists only in a circuit containing a capacitor

d) changes magnitude and direction periodically

20 / 50

20. The source voltage magnitude in a series circuit can be written as

21 / 50

21. A step-up transformer has . Its secondary is connected to a load. If , the primary current in ideal operation is

22 / 50

22. The impedance of a series circuit is given by

23 / 50

23. Study the table and select the suitable phasor interpretation.

Row	Phasor feature	Physical meaning
P	Length	Amplitude scale, such as peak value or rms value by convention
Q	Angular speed	Resistance of the wire
R	Projection	Frequency in
S	Angular separation	Peak-to-peak voltage only

a) Row Q

b) Row R

c) Row S

d) Row P

24 / 50

24. 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, Q, and R

c) P and R only

d) P and Q only

25 / 50

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

a) leads current and lags current

b) the inductor and capacitor always have equal voltages

c) the resistor voltage cancels both of them

d) the same current cannot pass through both and

26 / 50

26. 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 false, but Reason is true

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 true, but Reason is false

27 / 50

27. In notation, is different from because refers to

a) the instantaneous voltage only at

b) the maximum possible voltage in a cycle

c) the heating-equivalent voltage

d) the number of voltage cycles completed per second

28 / 50

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

29 / 50

29. A sinusoidal current has peak current . At one instant . This instant corresponds to

a) negative peak

b) rms value only

c) zero crossing

d) positive peak

30 / 50

30. The set of suitable statements for an ideal transformer is:
I.
II.
III. A step-up transformer has

a) I and II only

b) I, II, and III

c) I only

d) II and III only

31 / 50

31. 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

32 / 50

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

33 / 50

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

a) a pure capacitor

b) a real battery

c) a pure inductor

d) a pure resistor with fixed

34 / 50

34. A student says: “A step-up transformer increases voltage, so it also increases power.” The statement is unsuitable because an ideal step-up transformer

a) has zero secondary voltage

b) works only when no secondary coil is present

c) increases voltage while decreasing current

d) increases both voltage and current without any limit

35 / 50

35. In an circuit, the instantaneous voltage and current at a certain instant are and . The instantaneous power at that instant is

36 / 50

36. If and in a pure resistor, the instantaneous power is

37 / 50

37. For an ideal transformer with , a load is connected across the secondary. The effective resistance seen at the primary is

38 / 50

38. 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) above the horizontal reference line

b) opposite to the resistor voltage

c) along the horizontal line only

d) below the horizontal reference line

39 / 50

39. For an ideal transformer with , , and , the primary current is

40 / 50

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

a) a pure capacitor

b) a pure inductor

c) a pure resistor

d) a short copper wire only

41 / 50

41. 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:

42 / 50

42. The loss that is reduced by laminating the iron core of a transformer is mainly

a) loss due to zero secondary turns

b) eddy current loss

c) copper loss

d) loss due to absence of alternating flux

43 / 50

43. If the voltage across a pure capacitor is , a suitable expression for the current is

44 / 50

44. 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) resistance

b) inductive reactance

d) capacitive reactance

45 / 50

45. Consider the following statements about sinusoidal values.
I. is the maximum magnitude of current.
II. is the value of current at a particular instant.
III. is equal to for a symmetric sinusoidal current.

a) I, II, and III

b) I only

c) II and III only

d) I and II only

46 / 50

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

a) ,

b) ,

c) ,

d) ,

47 / 50

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

a) equal to the maximum current

c) zero

d) of the maximum current

48 / 50

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

49 / 50

49. 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 S

b) Row Q

c) Row P

d) Row R

50 / 50

50. At , a series circuit has , , and . The phase angle satisfies

a) , current leads voltage

b) , current lags voltage

c) , current lags voltage

d) , current leads voltage

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Alternating Current Mock Test – Class 12 Physics

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