CBSE Class 12th Physics Electromagnetic Induction 100 MCQs

Physics – Electromagnetic Induction

Class 12 Physics (Chapter 6) • 100 Multiple Choice Questions

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Question 1

What is the SI unit of magnetic flux?

Correct Answer: Weber

Question 2

Magnetic flux is a:

Correct Answer: Scalar quantity

Question 3

The dimensional formula for magnetic flux is:

Correct Answer: [M L² T⁻² A⁻¹]

Question 4

Electromagnetic induction is the phenomenon of producing an induced EMF by changing:

Correct Answer: Magnetic flux

Question 5

Faraday's law of electromagnetic induction gives the:

Correct Answer: Magnitude of induced EMF

Question 6

Lenz's law gives the:

Correct Answer: Direction of induced current

Question 7

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

Correct Answer: Energy

Question 8

The formula for induced EMF according to Faraday's law is:

Correct Answer: E = -dΦ/dt

Question 9

Motional EMF induced in a straight conductor of length L moving with velocity v perpendicular to magnetic field B is:

Correct Answer: E = BLv

Question 10

If a conductor moves parallel to the magnetic field, the induced EMF is:

Correct Answer: Zero

Question 11

The direction of induced current in a straight conductor moving in a magnetic field is given by:

Correct Answer: Fleming's Right Hand Rule

Question 12

Induced EMF can be produced by:

Correct Answer: All of the above

Question 13

1 Weber is equal to:

Correct Answer: 1 Tesla · meter²

Question 14

Eddy currents are also known as:

Correct Answer: Foucault currents

Question 15

Eddy currents are produced when:

Correct Answer: A metal is kept in a varying magnetic field

Question 16

Which of the following is NOT an application of eddy currents?

Correct Answer: X-ray crystallography

Question 17

Eddy currents in the core of transformers are minimized by:

Correct Answer: Using laminated iron core

Question 18

Self-induction is the property of a coil by which it opposes:

Correct Answer: Any change in the current flowing through itself

Question 19

The SI unit of self-inductance is:

Correct Answer: Henry

Question 20

One Henry is equivalent to:

Correct Answer: 1 Volt · second / Ampere

Question 21

Self-inductance of a long solenoid is proportional to:

Correct Answer: N²

Question 22

The formula for self-inductance (L) of an air-cored solenoid of length l, area A and N turns is:

Correct Answer: L = μ₀ N² A / l

Question 23

Energy stored in a current-carrying inductor is in the form of:

Correct Answer: Magnetic field

Question 24

The expression for energy (U) stored in an inductor of inductance L carrying current I is:

Correct Answer: U = 1/2 L I²

Question 25

If a soft iron core is inserted in a current-carrying solenoid, its self-inductance:

Correct Answer: Increases

Question 26

Mutual inductance of two coils depends on:

Correct Answer: Their geometry, separation, and orientation

Question 27

When two coils are placed far apart, their mutual inductance is:

Correct Answer: Minimum (almost zero)

Question 28

Mutual inductance between two coils is maximum when they are:

Correct Answer: Wound over each other (coaxial)

Question 29

Coefficient of coupling (k) for two tightly coupled coils is approximately:

Correct Answer: 1

Question 30

If two coils of inductances L₁ and L₂ are perfectly coupled, their mutual inductance M is:

Correct Answer: M = √(L₁ L₂)

Question 31

An AC generator converts:

Correct Answer: Mechanical energy into electrical energy

Question 32

An AC generator works on the principle of:

Correct Answer: Electromagnetic induction

Question 33

The peak value of EMF (E₀) induced in an AC generator coil is given by:

Correct Answer: NBAω

Question 34

If the angular speed (ω) of the armature of an AC generator is doubled, the peak induced EMF will:

Correct Answer: Double

Question 35

EMF induced in a coil rotating in a uniform magnetic field is maximum when:

Correct Answer: Plane of coil is parallel to B (Flux is 0, but dΦ/dt is maximum)

Question 36

EMF induced in a coil rotating in a uniform magnetic field is zero when:

Correct Answer: Plane of coil is perpendicular to B (Flux is max, but dΦ/dt is 0)

Question 37

Whenever magnetic flux linked with a closed circuit changes, an EMF is induced. This is:

Correct Answer: Faraday's First Law

Question 38

A magnetic field does NO work on a moving charge because:

Correct Answer: Force is perpendicular to velocity

Question 39

If a magnet is dropped through a vertical copper pipe, its acceleration will be:

Correct Answer: Less than g (Due to opposing Eddy currents)

Question 40

If an unmagnetized iron bar is dropped through a vertical copper pipe, its acceleration will be:

Correct Answer: Equal to g (No flux change, so no eddy currents)

Question 41

A conducting rod of length l rotates with angular speed ω about one end in a uniform magnetic field B parallel to its axis. The induced EMF is:

Correct Answer: 1/2 B ω l²

Question 42

In a coil, if current changes from 5A to 2A in 0.1s, generating 50V, what is its self-inductance L?

Correct Answer: 1.67 H (Since E = L di/dt => 50 = L(3/0.1) => L = 50/30 = 1.67 H)

Question 43

Two coils of self-inductances L₁ and L₂ are in series (assumed far apart). Equivalent inductance is:

Correct Answer: L₁ + L₂

Question 44

Two coils of self-inductances L₁ and L₂ are in parallel (assumed far apart). Equivalent inductance is:

Correct Answer: L₁ L₂ / (L₁ + L₂)

Question 45

A metal ring is kept in a magnetic field. If the field suddenly decreases, the ring will:

Correct Answer: Develop a current that tries to increase the field

Question 46

What is the dimensional formula for self-inductance L?

Correct Answer: [M L² T⁻² A⁻²]

Question 47

What is the dimensional formula for mutual inductance M?

Correct Answer: [M L² T⁻² A⁻²] (Same as Self-Inductance)

Question 48

When a core of high permeability is inserted in a solenoid, its inductance:

Correct Answer: Increases significantly

Question 49

The energy stored in an inductor is proportional to:

Correct Answer: Square of current (I²)

Question 50

Inductance in an electrical circuit is analogous to what in mechanics?

Correct Answer: Inertia (Mass)

Question 51

What happens when a copper plate is moved in and out of a strong magnetic field?

Correct Answer: It experiences a damping force due to eddy currents

Question 52

Flux passing through a coil is Φ = 3t² + 4t + 9. What is the induced EMF at t = 2s?

Correct Answer: -16 V (E = -dΦ/dt = -(6t + 4). At t=2, E = -16V)

Question 53

Which principle is used in an induction stove?

Correct Answer: Eddy currents

Question 54

Why are resistance boxes wound using doubled wire?

Correct Answer: To cancel self-inductance

Question 55

A spark is sometimes seen when a switch is opened. This is due to:

Correct Answer: High induced EMF due to self-inductance

Question 56

Unit of mutual inductance is:

Correct Answer: Henry

Question 57

For two long coaxial solenoids, the mutual inductance is proportional to:

Correct Answer: N₁ × N₂

Question 58

A rectangular loop is pulled out of a uniform magnetic field. The induced current is:

Correct Answer: Such that it opposes the pull

Question 59

When the North pole of a magnet is brought towards a closed coil, the face of the coil towards the magnet becomes a:

Correct Answer: North pole

Question 60

If a coil is open-circuited and flux changes through it, then:

Correct Answer: EMF is induced but no current flows

Question 61

Lenz's Law is essentially based on:

Correct Answer: Law of conservation of energy

Question 62

A magnetic field B is perpendicular to a coil of area A. If it is turned by 180°, the change in flux is:

Correct Answer: 2BA

Question 63

In an AC generator, slip rings are used to:

Correct Answer: Provide an alternating connection to the external circuit

Question 64

Which device uses mutual induction?

Correct Answer: Transformer

Question 65

Total charge induced in a circuit due to change in flux is given by:

Correct Answer: ΔQ = ΔΦ / R

Question 66

Does the induced charge depend on the time interval over which flux changes?

Correct Answer: No, it is independent of time

Question 67

The negative sign in Faraday's law represents:

Correct Answer: Lenz's Law

Question 68

To have a large mutual inductance, the two coils should be:

Correct Answer: Wound tightly over each other on a soft iron core

Question 69

Which of the following is true for an ideal inductor?

Correct Answer: It has zero resistance

Question 70

An inductor stores energy in its:

Correct Answer: Magnetic field

Question 71

If current I is doubled, energy stored in an inductor:

Correct Answer: Becomes four times

Question 72

Magnetic energy density (Energy per unit volume) in a magnetic field B is given by:

Correct Answer: B² / (2μ₀)

Question 73

In a given coil, back EMF is maximum when:

Correct Answer: Rate of change of current is maximum

Question 74

A train moves at constant speed from East to West. Will an EMF be induced across its axle?

Correct Answer: Yes, due to vertical component of Earth's field

Question 75

A 1m long conducting rod rotates with 50 rad/s in a B field of 0.2 T. Induced EMF between ends is:

Correct Answer: 5 V (E = 1/2 B ω L² = 0.5 × 0.2 × 50 × 1 = 5V)

Question 76

Which of these doesn't use electromagnetic induction?

Correct Answer: Electric Bulb

Question 77

When current in a coil changes from 10A to 5A in 0.1s, induced EMF is 10V. Find L:

Correct Answer: 0.2 H (10 = L * (5/0.1) => 10 = 50L => L = 0.2H)

Question 78

Which of the following is equivalent to Volt?

Correct Answer: Weber / second

Question 79

In a given coil, the induced charge depends on:

Correct Answer: Total change in flux and resistance (ΔQ = ΔΦ/R)

Question 80

Two closely wound coils have a mutual inductance of 1.5H. If current in one changes from 0 to 20A in 0.5s, the EMF induced in the second is:

Correct Answer: 60 V (E = M di/dt = 1.5 × 20/0.5 = 60V)

Question 81

As an iron core is placed inside a coil connected to an AC source, its inductive reactance:

Correct Answer: Increases

Question 82

What is the shape of the graph between induced EMF and rate of change of flux?

Correct Answer: Straight line passing through origin

Question 83

A 10H inductor carries a steady current of 2A. How much energy is stored?

Correct Answer: 20 J

Question 84

Which law is primarily used to find the direction of eddy currents?

Correct Answer: Lenz's Law

Question 85

A magnetic field in a region is increasing. A conducting ring in this region will experience:

Correct Answer: A tendency to contract (to reduce area and flux)

Question 86

A metallic plate is dropped in a magnetic field. It falls with:

Correct Answer: Acceleration < g

Question 87

A metallic coil has N turns and area A. If magnetic field changes by ΔB in time Δt, the average EMF is:

Correct Answer: -NA (ΔB/Δt)

Question 88

Induced EMF is independent of:

Correct Answer: Resistance of the circuit

Question 89

Which instrument is used to detect the presence of induced current?

Correct Answer: Galvanometer

Question 90

Induction heating works on the principle of:

Correct Answer: Eddy currents

Question 91

What is the EMF induced if a 2H inductor has a current changing at 5 A/s?

Correct Answer: 10 V

Question 92

When a magnet is moved into a coil, the magnitude of induced EMF depends upon:

Correct Answer: The speed with which the magnet is moved

Question 93

A varying magnetic flux through a coil produces:

Correct Answer: Both an induced EMF and an induced current (if closed)

Question 94

If a loop is rotated in a uniform magnetic field with angular velocity ω, the induced EMF frequency is:

Correct Answer: ω / 2π

Question 95

Self-inductance of a coil does not depend on:

Correct Answer: Current flowing through it

Question 96

Which of these demonstrates electromagnetic induction?

Correct Answer: Sparking in a switch (due to self-induction)

Question 97

A bicycle wheel has 10 metallic spokes. It rotates in a magnetic field parallel to its axis. The EMF induced across all spokes is:

Correct Answer: Same as EMF of one spoke (Spokes are in parallel)

Question 98

A copper ring is held horizontally and a bar magnet is dropped through it. The magnet's acceleration while passing through is:

Correct Answer: Less than g

Question 99

If the number of turns in a coil is doubled, its self-inductance becomes:

Correct Answer: Four times

Question 100

If a circuit has large self-inductance, turning off the switch:

Correct Answer: May cause a spark across the switch