physics MCQs - 12th class Chapter 04 Mcqs

1

The phenomenon of producing an induced emf due to the change in magnetic flux is called?

A

Electromagnetic Induction

B

Mutual Induction

C

Self-Induction

D

Motional EMF

2

Induced emf in a circuit lasts as long as the...

A

current is changing

B

magnetic flux is changing

C

resistance is constant

D

circuit is closed

3

The SI unit of mutual inductance and self-inductance is?

A

Weber

B

Tesla

C

Henry

D

Farad

4

Lenz's law is a consequence of the law of conservation of?

A

Mass

B

Charge

C

Energy

D

Momentum

5

The formula for energy stored in an inductor is given by?

A

E = ½ CV²

B

E = ½ LI²

C

E = I²R

D

E = VIt

6

An AC generator is a device that converts?

A

electrical energy into mechanical energy

B

mechanical energy into electrical energy

C

chemical energy into electrical energy

D

heat energy into electrical energy

7

The emf induced by the motion of a conductor across a magnetic field is known as?

A

Static EMF

B

Back EMF

C

Motional EMF

D

Variable EMF

8

The magnitude of motional emf is given by the formula?

A

ε = vBLcosθ

B

ε = vB/L

C

ε = ILBsinθ

D

ε = vBLsinθ

9

According to Faraday's law, the induced emf is equal to the negative rate of change of?

A

Electric Current

B

Electric Flux

C

Magnetic Flux

D

Magnetic Field

10

A transformer works on the principle of?

A

Self-Induction

B

Mutual Induction

C

Electrolysis

D

Motional EMF

11

In a step-up transformer, the number of turns in the secondary coil (Ns) is?

A

less than the primary (Np)

B

equal to the primary (Np)

C

greater than the primary (Np)

D

zero

12

The self-induced emf in a coil is also known as?

A

Forward emf

B

Motional emf

C

Primary emf

D

Back emf

13

To reduce power loss due to eddy currents, the core of a transformer is?

A

made of a single solid block

B

laminated

C

made of copper

D

kept in oil

14

In an ideal transformer, what quantity is conserved from primary to secondary?

A

Voltage

B

Current

C

Power

D

Magnetic Flux

15

The function of split rings in a DC generator is to?

A

act as slip rings

B

act as a commutator

C

reduce friction

D

increase magnetic field

16

The back emf in a DC motor increases as the?

A

load increases

B

speed of the motor increases

C

applied voltage decreases

D

resistance increases

17

Who discovered the phenomenon of electromagnetic induction in 1831?

A

Oersted

B

Ampere

C

Maxwell

D

Faraday and Henry

18

If a coil with N turns is used, the induced emf, according to Faraday's law, is given by?

A

ε = -ΔΦ/Δt

B

ε = -N(ΔΦ/Δt)

C

ε = N(Δt/ΔΦ)

D

ε = ΔΦ/(NΔt)

19

One henry is defined as the inductance in which a current change of one ampere per second results in an induced emf of?

A

one millivolt

B

one microvolt

C

one volt

D

ten volts

20

The energy in an inductor is stored in the form of a/an?

A

electric field

B

gravitational field

C

magnetic field

D

heat

21

The maximum emf produced by an AC generator is given by the formula?

A

ε₀ = NωA/B

B

ε₀ = NωAB

C

ε₀ = NAB/ω

D

ε₀ = NωB/A

22

For a DC motor, the current drawn is given by the formula?

A

I = (V+ε)/R

B

I = V/R

C

I = ε/R

D

I = (V-ε)/R

23

The current in a motor is largest when it is?

A

running at full speed

B

just starting up

C

running at half speed

D

switched off

24

A step-down transformer converts?

A

low voltage, high current to high voltage, low current

B

high voltage, low current to low voltage, high current

C

AC to DC

D

DC to AC

25

Hysteresis loss in a transformer is the energy used to?

A

heat the coils

B

overcome friction

C

magnetize and demagnetize the core

D

produce eddy currents

26

The product of induced current I and resistance R in a closed loop remains constant and is equal to?

A

induced power

B

induced charge

C

induced emf

D

magnetic force

27

For motional emf, the electric force qE is balanced by the magnetic force?

A

qB/v

B

qvL

C

qvB

D

qE/B

28

The term ΔI/Δt represents the?

A

change in inductance

B

rate of change of current

C

total current

D

change in time

29

In an AC generator, the induced current is sinusoidal and reverses its direction f times per...?

A

minute

B

rotation

C

second

D

hour

30

The assembly of coils wound around an iron cylinder in a generator or motor is called a/an?

A

commutator

B

slip ring

C

armature

D

stator

31

What device is used to make the output of a generator unidirectional?

A

Slip rings

B

A rheostat

C

A split-ring commutator

D

A capacitor

32

The back motor effect in a generator produces a?

A

counter torque

B

forward torque

C

constant speed

D

zero force

33

The windings of an electromagnet in a motor are called?

A

armature coils

B

primary coils

C

field coils

D

secondary coils

34

For a transformer, the ratio Vs/Vp is equal to?

A

Ip/Is

B

Is/Ip

C

Np/Ns

D

Ns/Np

35

The main reason to use high voltage for long-distance power transmission is to?

A

increase power

B

reduce current and power loss

C

increase resistance

D

reduce voltage drops

36

The changing magnetic flux associated with the primary coil is also linked with the secondary coil in which phenomenon?

A

Self-Induction

B

Mutual Induction

C

Capacitance

D

Resistance

37

In an AC circuit, inductors behave like?

A

capacitors

B

diodes

C

resistors

D

batteries

38

The energy density (energy per unit volume) in a solenoid is proportional to?

A

B

1/B

C

B²

D

1/B²

39

The angular speed ω of an AC generator is related to its frequency f by?

A

ω = 2π/f

B

ω = f/2π

C

ω = 2πf

D

ω = πf

40

If the magnetic field is parallel to the velocity of a conductor, the motional emf will be?

A

maximum

B

minimum

C

zero

D

infinite

41

A metal rod of length L is moving at speed v perpendicular to a magnetic field B. The induced emf is?

A

B²vL

B

Bv²L

C

BvL

D

BvL²

42

If a magnet is pushed into a coil, the induced current's magnetic field will?

A

attract the magnet

B

repel the magnet

C

have no effect

D

be parallel to the magnet's field

43

The constant of proportionality 'M' in the mutual induction formula depends on?

A

current only

B

voltage only

C

geometrical factors of the coils

D

resistance of the coils

44

The self-inductance L of a coil can be increased by inserting a core made of?

A

wood

B

plastic

C

air

D

ferromagnetic material

45

A DC motor is a device which converts electrical energy into?

A

mechanical energy

B

chemical energy

C

sound energy

D

light energy

46

If the secondary circuit of a transformer is open, the current in the primary is?

A

very large

B

zero

C

maximum

D

very small

47

The formula ε = NωABsin(ωt) describes the emf for a/an?

A

DC Motor

B

Transformer

C

DC Generator

D

AC Generator

48

What happens to the induced current in a loop if its resistance is doubled while the speed of motion is kept constant?

A

It is doubled

B

It is halved

C

It remains the same

D

It becomes zero

49

The direction of induced current in a conductor moving in a magnetic field can be found using?

A

Left-hand rule

B

Right-hand rule

C

Ohm's law

D

Kirchhoff's law