Physics Alternating Current MCQs Chapter 5 Class 12 - PLS Academy

Physics Alternating Current MCQs Chapter 5 Class 12

Physics Alternating Current (AC) is an important chapter of Class 12 Physics and plays a crucial role in free preparations for entry tests and FSC Part-II exams. It is commonly tested in MDCAT, NUMS, AKU, NUST, UET ECAT, and FSC examinations. This chapter covers key topics such as AC voltage and current, RMS and peak values, reactance, impedance, and resonance in AC circuits. Many students rely on entry test MCQs and practice tests to strengthen their understanding of these concepts.

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Created on February 07, 2022 By Ali Durrani

Physics Ch 16 Class 12 Alternating Current

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1 / 73

Which of the following color has the highest energy?

Blue

Green

Violet

Yellow

2 / 73

Consider two capacitors with capacitance 2µF and 4µF. With which type of connection will the 4µF capacitor have a greater amount of stored energy than the 2µF capacitor?

PMC Practice 2
Physics
Alternating Current
Elimination Tool:

A) Series

B) Parallel

C) Either series or parallel

D) Neither series nor parallel

3 / 73

Mutual inductance has a practical role in performance of:

PMC Practice 4
Physics
Alternating Current
Elimination Tool:

A) AC generator

B) Radio choke

C) DC generator

D) Transformer

4 / 73

Power factor of the pure capacitive circuit is?

-1

0.5

5 / 73

The bridge rectifier is preferred to an ordinary two diode full-wave rectifier because?

PMC Practice 2
Physics
Alternating Current
Elimination Tool:

A) It needs a much smaller transformer for the same output

B) No center tap required

C) Less PIV rating per diode

D) All of the above options are correct

6 / 73

In electronic circuits, a PN junction diode is used to convert alternating current into direct current. This process is called:

NTS 2018
Physics
Alternating Current
Elimination Tool:

A) Rectification

B) Amplification

C) Doping

D) Integrated Circuit

7 / 73

The ripple factor of a half-wave rectifier is:

PMC Practice 2
Physics
Alternating Current
Elimination Tool:

A) 1.21

B) 0.8

C) 0.6

D) 0.4

8 / 73

Current that fluctuates periodically with time is ——

PMC Practice 4
Physics
Alternating Current
Elimination Tool:

A) DC current

B) BC current

C) ACcurrent

D) Magnetic current

9 / 73

RLC circuit can be excited by

Both a and b

None of these

10 / 73

The use of a capacitor filter in a rectifier circuit gives satisfactory performance only when the load:

PMC Practice 3
Physics
Alternating Current
Elimination Tool:

A) Current is high

B) Current is low

C) Voltage is high

D) Voltage is low

11 / 73

A full wave rectifier is operating from 50 Hz mains. Fundamental frequency of ripple will be:

PMC Practice 1
Physics
Alternating Current
Elimination Tool:

A) 100 Hz

B) 25 Hz

C) 50 Hz

D) 200 Hz

12 / 73

In a full-wave rectification, the number of diodes used are:

PMC 2020
Physics
Alternating Current
Elimination Tool:

A) 1

B) 2

C) 3

D) 4

13 / 73

Power factor in an AC circuit Is?

cos theta

sin theta

tan theta

None of these

14 / 73

Wavelength of X-rays is of the order of?

Centimeter

Micron

Angstrom (10^-6 m)

Meter

15 / 73

An Inductor of 1H Is connected across a 220V, 50Hz supply. The peak value of current is approximately:

0.5A

0.7A

1.4A

16 / 73

In a step up transformer ________.

NTS 2019
Physics
Alternating Current
Elimination Tool:

A) Vs > Vp while Is > Ip

B) Vs Ip

C) Vs = Vp while Is > Ip

D) Vs > Vp while Is < Ip

17 / 73

Power factor. of RLC circuit at Resonance Is

-1

0.5

18 / 73

Voltage after which in forward bias current start to rise with increase in voltage is called:

PMC Sample 3
Physics
Alternating Current
Elimination Tool:

A) Breakdown voltage

B) Reverse voltage

C) Forward voltage

D) Knee voltage

19 / 73

In a practical transformer mutual induction between primary and secondary coils takes place. In such transformer what can be deduced about the power.

UHS 2018
Physics
Alternating Current
Work, Power & Energy
Elimination Tool:

A) Power output = Power input

B) Power output > Power input

C) Power output ≥ Power input

D) Power output < Power input

20 / 73

Impedance of a circuit Is calculated as:

Vrms/Irms

Irms/Vrms

IrmsVrms

Vrms/R

21 / 73

Electromagnetic waves are produced due to flow of

Negative charge

Positive charge

Both a and b

None of these

22 / 73

The frequency of AC used in Pakistan is

30c/s

50 c/s

90c/s

180c/s

23 / 73

Reactance of an Inductor Is given by:

1/wL

1/wC

24 / 73

Step up transformer have ________ turns in secondary coil.

PMC Practice 1
Physics
Alternating Current
Elimination Tool:

A) More

B) Less

C) Equal

D) Zero

25 / 73

Transformer is used in rectification to ___________ the supply voltage.

PMC Practice 5
Physics
Alternating Current
Elimination Tool:

A) Step up

B) Step down

C) Equalize

D) None of these options is correct

26 / 73

The process of combining low frequency waves with high frequency is called:

Rectification

Amplification

Modulation

Magnification

27 / 73

Simple oscillating circuit consists of?

Inductor & Capacitor

Resistance & capacitor

Resistance & coil

Inductor and resistance

28 / 73

The principle of a capacitor is based on which of the following facts?

NTS 2011
Physics
Alternating Current
Elimination Tool:

A) potential of a conductor is greatly increased with a decrease in the charge in it increase in the charge in it. affecting the charge in it

B) potential of a conductor is greatly reduced with an increase in the charge in it.

C) potential of a conductor is greatly increased without affecting the charge in it

D) potential of a conductor is greatly reduced without affecting the charge in it

29 / 73

In a step-down transformer, the current in the primary coil is ______ than that in the secondary coil.

PMC 2021 Tested
Physics
Alternating Current
Elimination Tool:

A) None of these

B) More

C) Equal

D) Less

30 / 73

P = Irms Vrms Is applicable for

AC only

DC only

Both a and b

None of these

31 / 73

What is the range of typical band gap in conductors

PMC Sample 3
Physics
Alternating Current
Elimination Tool:

A) 100-1000eV

B) 0.5-10eV

C) 0.01-0.1 eV

D) 10000-10000000eV

32 / 73

In which rectifier is the ripple factor less?

PMC Practice 1
Physics
Alternating Current
Elimination Tool:

A) Full wave

B) Half wave

C) Both A and B

D) None of them

33 / 73

The number of diodes in bridge rectifier is

PMC Sample 3
Physics
Alternating Current
Elimination Tool:

A) 4

B) 3

C) 2

D) 5

34 / 73

If the instantaneous current in a circuit is given by I = A sin (wt) ampere, the RMS value of the current is:

PMC Practice 3
Physics
Alternating Current
Elimination Tool:

A) 2A

B) A/√2

C) 2√2A

D) Zero

35 / 73

What will be the Impedance for V = 10 sin(wt) and I = 20 sln(wt)

200 ohm

2 ohm

0.5 ohm

0.707 ohm

36 / 73

The direction of current through the load resistance of a full-wave rectification circuit:

UHS 2019
Physics
Alternating Current
Elimination Tool:

A) remains constant

B) inverts for positive cycle

C) changes for every cycle

D) inverts for negative cycle

37 / 73

A half wave rectifier is operating from 50 Hz mains, fundamental frequency of ripple will be

PMC Sample 3
Physics
Alternating Current
Elimination Tool:

A) 100 Hz

B) 25 Hz

C) 200Hz

D) 50Hz

38 / 73

In a pure resistive circuit current and voltage are

In phase

Out of phase

Current leads

Voltage leads

39 / 73

In RLC series circuit at resonance, the A.C voltage across Resistance R, Inductance L and capacitance C are 5V, 10V and 10 V respectively. The A.C voltage applied to the circuit will be:

NUMS 2015
Physics
Alternating Current
Elimination Tool:

A) 20 V

B) 10 V

C) 5 V

D) 25 V

40 / 73

PIV stands for :

PMC 2020
Physics
Alternating Current
Elimination Tool:

A) Positive inverse voltage

B) Pawn Bh Integrated voltage

C) Peak inverse voltage

D) Peak integrated voltage

41 / 73

For an ideal step-up transformer Ps ——- Pp.

PMC Practice 8
Physics
Alternating Current
Elimination Tool:

A) Equal to

B) Greater than

C) Less than

D) None of these

42 / 73

Voltage Is current In RC circuit.

Leading

Lagging

In Phase

None of these

43 / 73

Alternating Current Generators use:

PMC Practice 5
Physics
Alternating Current
Elimination Tool:

A) Coiled rings

B) Split rings

C) Slip rings

D) Solenoid rings

44 / 73

What is the instantaneous power dissipated through a resistor of resistance 10 ohm if it is connected to an AC source of frequency 15 Hz at 1/180 sec if peak value is 20 V?

UHS 2018
Physics
Alternating Current
Elimination Tool:

A) 10 W

B) 100 W

C) 40 W

D) Cannot be determined

45 / 73

If a half wave rectifier is used to convert 50Hz AC into DC, then the number of pulses present in rectified voltage is:

PMC Sample 1
Physics
Alternating Current
Elimination Tool:

A) 25

B) 50

C) 100

D) 75

46 / 73

Power of RCL circuit at resonance Is?

Zero

Minimum

Maximum

None of these

47 / 73

The rectifier is a device which converts?

PMC Practice 3
Physics
Alternating Current
Elimination Tool:

A) AC to DC

B) DC to AC

C) AC to triangular current

D) DC to triangular current

48 / 73

At resonance, the RLC circuit behaves like:

Pure Inductive

Pure Resistive

Pure Capacitive

All of these

49 / 73

Half wave voltage multipliers can provide what degree of voltage multiplication?

PMC Practice 4
Physics
Alternating Current
Elimination Tool:

A) Any doubler

B) Any tripler

C) Any multiplication

D) None of them

50 / 73

The frequency of applied AC is 2 kHz. Its time period will be:

PMC Practice 3
Physics
Alternating Current
Elimination Tool:

A) 0.5 x 10-3 sec

B) 0.5 second

C) 5 sec

D) 2 sec

51 / 73

Impedance in RLC series circuit Is given by

52 / 73

Which of the following are component of half wave rectifier?

PMC Practice 1
Physics
Alternating Current
Elimination Tool:

A) Transformer

B) Load resistance

C) Power supply

D) All of the above

53 / 73

In case of half wave rectification the resistance of diode during negative half of A.C is:

UHS 2018
Physics
Alternating Current
Elimination Tool:

A) Very high

B) Very low

C) A few ohms

D) Negative

54 / 73

The principle of an AC generator is.

NTS 2019
Physics
Alternating Current
Elimination Tool:

A) Lenz's law

B) Faraday's Law

C) Self-induction

D) Ampere's law

55 / 73

Which of the following remains unchanged in a transformer.

PMC Sample 3
Physics
Alternating Current
Elimination Tool:

A) Voltage

B) Current

C) Power

D) Capacitance

56 / 73

The angle made by the coil of an AC generator at a time Interval 3T/4 is?

2ℼ

2/ℼ

3ℼ/2

ℼ

57 / 73

If a half-wave rectifier is used to convert 50 Hz AC into DC, then the number of pulses present in the rectifier voltage is:

PMC Practice 2
Physics
Alternating Current
Elimination Tool:

A) 25

B) 50

C) 100

D) 75

58 / 73

An alternating voltage source is connected to a resistor R, and a capacitor C, then which of the following statements about phase angle between voltage V and current I is correct?

NUMS 2019 Cancelled
Physics
Alternating Current
Elimination Tool:

A) In the resistor, I leads V by 90 degrees – In the capacitor, I leads V by 90 degrees

B) In the resistor, I lags V by 90 degrees – In the capacitor, I leads V by 90 degrees

C) In the resistor, I and V are in phase – In the capacitor, I leads V by 90 degrees

D) In the resistor, I and V are in phase – In the capacitor, I lags V by 90 degrees

59 / 73

A diode works in _______ bias for rectification.

PMC Practice 6
Physics
Alternating Current
Elimination Tool:

A) Forward

B) Reverse

C) Mid

D) Positive

60 / 73

The AC generator is similar to:

PMC 2021 Tested
Physics
Alternating Current
Elimination Tool:

A) Transformer

B) None of these

C) Inductor

D) Capacitor

61 / 73

An alternation voltage V (in volts) is represented by the equation:
V = 300 sin (100πt)
What is the value of “f” for this voltage?

UHS 2019
Physics
Alternating Current
Elimination Tool:

A) 100 Hz

B) 50 Hz

C) 25 H

D) 200 Hz

62 / 73

If an AC voltage of rms value of 10 volts is applied as input of a half-wave rectifier, then the voltage value of the DC output will be:

PMC Practice 4
Physics
Alternating Current
Elimination Tool:

A) 10 V

B) 10.3 V

C) 10.7 V

D) 9.3 V

63 / 73

The maximum instantaneous value measured from zero value is known as?

PMC Sample 3
Physics
Alternating Current
Elimination Tool:

A) peak value

B) peak to peak value

C) cycle

D) period

64 / 73

X-rays have frequency greater than

Visible light

Ultraviolet

Microwaves

All of these

65 / 73

In a half wave rectifier, the diode conducts during:

NUMS 2019 Reconduct
Physics
Alternating Current
Elimination Tool:

A) One half of the input cycle

B) A portion of the positive half of the input cycle

C) A portion of the negative half of the input cycle

D) Both halves of the input cycles

66 / 73

If the peak voltage is 9V, calculate the peak to peak voltage.

PMC Practice 8
Physics
Alternating Current
Elimination Tool:

A) 9V

B) 18V

C) 4.5V

D) 0V

67 / 73

The maximum efficiency of a half-wave rectifier is:

PMC Practice 3
Physics
Alternating Current
Elimination Tool:

A) 80.6 %

B) 40.6 %

C) 70 %

D) 50 %

68 / 73

Resistance of RCL series circuit at resonance Is?

Xi R Xc

69 / 73

In a bridge type full-wave rectifier, if Vm is the peak voltage across the secondary coil of the transformer, the maximum voltage coming across each reverse biased diode is:

PMC Practice 5
Physics
Alternating Current
Elimination Tool:

A) Vm

B) Vm/√2

C) 2Vm

D) Vm3

70 / 73

Identify the factor on which mutual inductance does not depend:

PMC Practice 3
Physics
Alternating Current
Elimination Tool:

A) Relative orientation

B) Relative separation of two coils

C) Reciprocity

D) Permeability of the core material

71 / 73

that the supply for the potentiometer is taken?

PMC Practice 8
Physics
Alternating Current
Elimination Tool:

A) From a source which is not the same as the unknown voltage

B) From a battery

C) From the same source as the unknown voltage

D) Any of the above

72 / 73

The output voltage of a rectifier is:

PMC Practice 4
Physics
Alternating Current
Elimination Tool:

A) Smooth

B) Pulsating

C) Perfectly direct

D) Alternating

73 / 73

A circuit that adds positive or negative D.C. voltage to an input sine wave is called:

PMC Practice 4
Physics
Alternating Current
Elimination Tool:

A) Clamper

B) Clipper

C) Diode clamp

D) Limiter

Your score is

The average score is 55%

Importance of Alternating Current MCQs

Understanding Alternating Current helps students analyze AC circuits and solve related numerical problems. Moreover, exam questions frequently focus on formula application, phase relationships, and resonance conditions. Practicing topic-wise MCQs and short tests improves speed, accuracy, and confidence. As a result, students can handle tricky AC questions efficiently in competitive exams.

Effective Strategy for Free Preparations

Students should revise formulas, understand key concepts, and attempt chapter-wise MCQs regularly. In addition, solving free tests and past papers helps identify frequently asked questions and repeated patterns. PLS Academy provides structured resources that support free entry test preparations for Physics Alternating Current and other Class 12 Physics chapters.

JazakAllah.