⚡ Master "Electromagnetic Induction" with 100 MCQs (Set - 3) ⚡
⚡ From Basic to Expert Level! ⚡
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Are you preparing for exams or aiming to strengthen your understanding of Physics – Electromagnetic Induction? Looking for a complete set of 100 high-quality MCQs from basic to expert level to sharpen your concepts and boost your exam confidence?
This carefully curated collection of Multiple Choice Questions (MCQs) covers all major topics of the unit, including:
• Magnetic Flux & Faraday’s Laws
• Lenz’s Law & Induced EMF
• Motional EMF
• Self Induction & Mutual Induction
• Inductance & Energy Stored in an Inductor
• AC Generators & Transformers
• RL Circuits & Time Constant
• Eddy Currents & Magnetic Braking
• Fleming’s Left & Right Hand Rules
• Applications of Electromagnetic Induction
Each MCQ is provided with a clear solution or explanation, helping you:
- Understand concepts step-by-step
- Improve numerical problem-solving skills
- Revise quickly before exams
- Build strong conceptual clarity
Whether you’re revising for school exams, board exams, or competitive entry tests, this comprehensive MCQ set is designed to take your preparation to the next level.
💡 Study Tip: Start with basic questions, move to moderate, and finally challenge yourself with expert-level MCQs for maximum learning and exam readiness.
Are you preparing for exams or aiming to strengthen your understanding of Physics – Electromagnetic Induction? Looking for a complete set of 100 high-quality MCQs from basic to expert level to sharpen your concepts and boost your exam confidence?
This carefully curated collection of Multiple Choice Questions (MCQs) covers all major topics of the unit, including:
• Magnetic Flux & Faraday’s Laws
• Lenz’s Law & Induced EMF
• Motional EMF
• Self Induction & Mutual Induction
• Inductance & Energy Stored in an Inductor
• AC Generators & Transformers
• RL Circuits & Time Constant
• Eddy Currents & Magnetic Braking
• Fleming’s Left & Right Hand Rules
• Applications of Electromagnetic Induction
Each MCQ is provided with a clear solution or explanation, helping you:
- Understand concepts step-by-step
- Improve numerical problem-solving skills
- Revise quickly before exams
- Build strong conceptual clarity
Whether you’re revising for school exams, board exams, or competitive entry tests, this comprehensive MCQ set is designed to take your preparation to the next level.
💡 Study Tip: Start with basic questions, move to moderate, and finally challenge yourself with expert-level MCQs for maximum learning and exam readiness.
What You’ll Get in this post:
Set-1: Basic Level – Perfect for beginners, focusing on fundamentals like Magnetic Flux, Faraday’s Law, Lenz’s Law, and Force on a Current Carrying Conductor.
Set-2: Intermediate Level – Strengthens application skills with Motional EMF, Ampere’s Law, Solenoids, Motion of Charged Particles, and Velocity Selector.
Set-3: Advanced Level – Develops deeper understanding through Torque on a Current-Carrying Coil, Determination of e/m for an Electron, Galvanometer Conversions, and Measurement Instruments (Ammeter, Voltmeter, Avometer).
Set-4: Expert Level – High-level conceptual and numerical MCQs covering the entire Electromagnetic Induction unit, designed to test speed, accuracy, and critical thinking.
Electromagnetic Induction MCQs (Set-1: Basic Level
Set–1 (Basic to Strong Foundation) – MCQs 1–25
MCQ No. 1
Magnetic flux is maximum when angle between magnetic field and area vector is:
a) 30°
b) 45°
c) 60°
d) 0°
Correct answer: d) 0°
Explanation:
Flux Φ = BA cosθ. Maximum when cosθ = 1 → θ = 0°.
MCQ No. 2
If magnetic field is tripled while area is halved, flux becomes:
a) Same
b) 1.5 times
c) 3 times
d) 6 times
Correct answer: b) 1.5 times
Explanation:
New flux = (3B)(A/2) = 3/2 BA = 1.5 BA.
MCQ No. 3
Induced emf is zero when:
a) Flux is large
b) Flux is small
c) Flux is constant
d) Flux is negative
Correct answer: c) Flux is constant
Explanation:
Emf depends on rate of change of flux, not magnitude.
MCQ No. 4
Faraday’s law mathematically is:
a) ε = NΦ
b) ε = −N dΦ/dt
c) ε = Φ/N
d) ε = N/Φ
Correct answer: b) ε = −N dΦ/dt
Explanation:
This is the fundamental law of electromagnetic induction.
MCQ No. 5
The negative sign in Faraday’s law represents:
a) Voltage drop
b) Current direction
c) Opposition to change
d) Resistance
Correct answer: c) Opposition to change
Explanation:
It represents Lenz’s law.
MCQ No. 6
A magnet moved slowly toward a coil produces emf that is:
a) Large
b) Small
c) Zero
d) Infinite
Correct answer: b) Small
Explanation:
Slower motion → smaller rate of change of flux → smaller emf.
MCQ No. 7
If magnet speed doubles, induced emf becomes:
a) Same
b) Half
c) Double
d) Four times
Correct answer: c) Double
Explanation:
Emf ∝ rate of change of flux ∝ speed.
MCQ No. 8
Motional emf depends on all EXCEPT:
a) Magnetic field
b) Length of conductor
c) Velocity
d) Resistance
Correct answer: d) Resistance
Explanation:
ε = Blv; resistance affects current, not emf.
MCQ No. 9
Unit of dΦ/dt is:
a) Tesla
b) Volt
c) Henry
d) Ampere
Correct answer: b) Volt
Explanation:
Rate of change of flux gives induced emf (Volt).
MCQ No. 10
If number of turns becomes three times, emf becomes:
a) Same
b) Double
c) Triple
d) Nine times
Correct answer: c) Triple
Explanation:
ε ∝ N.
MCQ No. 11
Self induction is also called:
a) Mutual induction
b) Back emf
c) Forward emf
d) Static emf
Correct answer: b) Back emf
Explanation:
It opposes change in its own current.
MCQ No. 12
When current decreases rapidly in a coil, induced emf:
a) Is small
b) Is large
c) Is zero
d) Remains constant
Correct answer: b) Is large
Explanation:
Large dI/dt produces large induced emf.
MCQ No. 13
Inductance of air-core solenoid increases if:
a) Length increases
b) Turns increase
c) Area decreases
d) Current increases
Correct answer: b) Turns increase
Explanation:
L ∝ N².
MCQ No. 14
Energy stored in 1 H inductor carrying 2 A is:
a) 1 J
b) 2 J
c) 4 J
d) 0.5 J
Correct answer: b) 2 J
Explanation:
U = ½ LI² = ½ × 1 × 4 = 2 J.
MCQ No. 15
Time constant of RL circuit depends on:
a) Voltage
b) Inductance
c) Resistance
d) Both b and c
Correct answer: d) Both b and c
Explanation:
τ = L/R.
MCQ No. 16
In RL circuit, after long time, current becomes:
a) Zero
b) Maximum steady
c) Infinite
d) Alternating
Correct answer: b) Maximum steady
Explanation:
Inductor behaves like ordinary wire after steady state.
MCQ No. 17
Transformer works on principle of:
a) Self induction
b) Mutual induction
c) Electrostatics
d) Resistance
Correct answer: b) Mutual induction
Explanation:
Changing current in primary induces emf in secondary.
MCQ No. 18
Step-up transformer increases:
a) Current
b) Voltage
c) Resistance
d) Power
Correct answer: b) Voltage
Explanation:
Turns ratio increases voltage.
MCQ No. 19
If primary turns are greater than secondary, transformer is:
a) Step-up
b) Step-down
c) Isolation
d) DC
Correct answer: b) Step-down
Explanation:
Voltage proportional to turns.
MCQ No. 20
Eddy currents cause:
a) Cooling
b) Heating
c) No effect
d) Superconductivity
Correct answer: b) Heating
Explanation:
Circulating currents produce Joule heating.
MCQ No. 21
Laminated core reduces:
a) Flux
b) Inductance
c) Eddy currents
d) Voltage
Correct answer: c) Eddy currents
Explanation:
Lamination increases resistance to eddy currents.
MCQ No. 22
Magnetic braking works due to:
a) Resistance
b) Capacitance
c) Eddy currents
d) Voltage
Correct answer: c) Eddy currents
Explanation:
Induced currents oppose motion.
MCQ No. 23
If frequency increases, inductive reactance:
a) Decreases
b) Increases
c) Remains same
d) Zero
Correct answer: b) Increases
Explanation:
XL = 2πfL.
MCQ No. 24
In pure inductor, power factor is:
a) 1
b) 0
c) 0.5
d) Infinite
Correct answer: b) 0
Explanation:
Current lags by 90°, so average power is zero.
MCQ No. 25
If magnetic field is suddenly switched off, induced emf will be:
a) Zero
b) Momentary
c) Constant
d) Increasing
Correct answer: b) Momentary
Explanation:
Sudden change in flux produces instantaneous emf.
Set–2 (Intermediate – More Numericals & Applications)
Electromagnetic Induction – MCQs 26–50
MCQ No. 26
A magnetic flux through a coil changes from 0.2 Wb to 0 in 0.1 s. If the number of turns is 50, induced emf is:
a) 50 V
b) 100 V
c) 75 V
d) 25 V
Correct answer: b) 100 V
Explanation:
E = N(ΔΦ/Δt) = 50 × (0.2 / 0.1) = 50 × 2 = 100 V.
MCQ No. 27
A circular coil rotates in a uniform magnetic field. Maximum induced emf occurs when the plane of coil is:
a) Parallel to field
b) Perpendicular to field
c) At 45°
d) At 60°
Correct answer: a) Parallel to field
Explanation:
Emf is maximum when rate of change of flux is maximum, which occurs when plane is parallel to B (flux changing fastest).
MCQ No. 28
A straight conductor of length 0.5 m moves with velocity 4 m/s perpendicular to a magnetic field of 0.2 T. Induced emf is:
a) 0.4 V
b) 0.2 V
c) 0.8 V
d) 1.0 V
Correct answer: a) 0.4 V
Explanation:
E = Bℓv = 0.2 × 0.5 × 4 = 0.4 V.
MCQ No. 29
If speed of conductor in magnetic field doubles, induced emf becomes:
a) Half
b) Same
c) Double
d) Four times
Correct answer: c) Double
Explanation:
E = Bℓv, so emf is directly proportional to velocity.
MCQ No. 30
When magnetic flux through a coil remains constant, induced emf is:
a) Maximum
b) Minimum
c) Zero
d) Infinite
Correct answer: c) Zero
Explanation:
From Faraday’s Law, emf ∝ rate of change of flux. If flux is constant, emf is zero.
MCQ No. 31
The unit of magnetic flux is:
a) Tesla
b) Weber
c) Henry
d) Ohm
Correct answer: b) Weber
Explanation:
Magnetic flux is measured in Weber (Wb).
MCQ No. 32
A 200-turn coil experiences change in flux of 0.05 Wb in 0.5 s. Induced emf:
a) 10 V
b) 20 V
c) 5 V
d) 50 V
Correct answer: b) 20 V
Explanation:
E = N(ΔΦ/Δt) = 200 × (0.05 / 0.5) = 200 × 0.1 = 20 V.
MCQ No. 33
Self inductance depends on:
a) Shape of coil
b) Number of turns
c) Magnetic core
d) All of these
Correct answer: d) All of these
Explanation:
L depends on N², geometry, and permeability of core material.
MCQ No. 34
Unit of self-inductance is:
a) Tesla
b) Weber
c) Henry
d) Volt
Correct answer: c) Henry
Explanation:
Self-inductance is measured in Henry (H).
MCQ No. 35
Energy stored in inductor is:
a) LI
b) ½LI
c) ½LI²
d) LI²
Correct answer: c) ½LI²
Explanation:
Magnetic energy stored = ½LI².
MCQ No. 36
If current through inductor increases, induced emf:
a) Aids increase
b) Opposes increase
c) Zero
d) Constant
Correct answer: b) Opposes increase
Explanation:
By Lenz’s law, induced emf always opposes change in current.
MCQ No. 37
A transformer works on principle of:
a) Mutual induction
b) Self induction
c) Electrostatics
d) Resistance
Correct answer: a) Mutual induction
Explanation:
Transformer transfers energy using mutual induction between two coils.
MCQ No. 38
Step-up transformer increases:
a) Current
b) Voltage
c) Power
d) Frequency
Correct answer: b) Voltage
Explanation:
In step-up transformer, Ns > Np, so output voltage increases.
MCQ No. 39
In ideal transformer:
a) Input power > Output power
b) Output power > Input power
c) Input power = Output power
d) Power is lost
Correct answer: c) Input power = Output power
Explanation:
Ideal transformer has no losses, so Pin = Pout.
MCQ No. 40
If number of secondary turns is half of primary turns, transformer is:
a) Step-up
b) Step-down
c) Isolation
d) Power
Correct answer: b) Step-down
Explanation:
Voltage is proportional to turns. Fewer turns → lower voltage.
MCQ No. 41
Induced current direction is determined by:
a) Fleming’s left-hand rule
b) Fleming’s right-hand rule
c) Ohm’s law
d) Ampere’s law
Correct answer: b) Fleming’s right-hand rule
Explanation:
Right-hand rule gives direction of induced current in generator.
MCQ No. 42
If frequency of AC source increases, inductive reactance:
a) Decreases
b) Remains same
c) Increases
d) Becomes zero
Correct answer: c) Increases
Explanation:
XL = 2πfL, so proportional to frequency.
MCQ No. 43
If inductance doubles and frequency doubles, XL becomes:
a) Same
b) Double
c) Four times
d) Half
Correct answer: c) Four times
Explanation:
XL = 2πfL. If both f and L double → XL becomes 4 times.
MCQ No. 44
Eddy currents can be reduced by:
a) Increasing thickness
b) Laminating core
c) Using copper core
d) Increasing flux
Correct answer: b) Laminating core
Explanation:
Laminations increase resistance and reduce eddy current loss.
MCQ No. 45
When magnet is pushed into coil quickly, induced emf is:
a) Smaller
b) Larger
c) Same
d) Zero
Correct answer: b) Larger
Explanation:
Faster change in flux → larger induced emf.
MCQ No. 46
Back emf in motor is due to:
a) Self induction
b) Mutual induction
c) Capacitance
d) Resistance
Correct answer: a) Self induction
Explanation:
Motor coil rotating in magnetic field produces back emf by self-induction.
MCQ No. 47
The time constant of RL circuit is:
a) R/L
b) L/R
c) 1/RL
d) RL
Correct answer: b) L/R
Explanation:
Time constant τ = L/R.
MCQ No. 48
If resistance increases in RL circuit, time constant:
a) Increases
b) Decreases
c) Same
d) Infinite
Correct answer: b) Decreases
Explanation:
τ = L/R. Increasing R decreases τ.
MCQ No. 49
When current becomes steady in inductor:
a) emf maximum
b) emf zero
c) emf constant
d) emf infinite
Correct answer: b) emf zero
Explanation:
When current is constant, dI/dt = 0 → induced emf = 0.
MCQ No. 50
Electromagnetic induction was discovered by:
a) James Clerk Maxwell
b) Michael Faraday
c) Ampere
d) Henry
Correct answer: b) Michael Faraday
Explanation:
Electromagnetic induction was experimentally discovered by Michael Faraday in 1831.
Set–3 (Advanced Level – High Numericals & Mixed Concepts)
Electromagnetic Induction – MCQs 51–75
MCQ No. 51
A coil of inductance 2 H carries a current of 5 A. Energy stored in the magnetic field is:
a) 10 J
b) 25 J
c) 50 J
d) 5 J
Correct answer: b) 25 J
Explanation:
Energy stored = ½LI² = ½ × 2 × (5)² = 1 × 25 = 25 J.
MCQ No. 52
A 500-turn coil has area 0.02 m² placed in a magnetic field of 0.5 T perpendicular to it. If field becomes zero in 0.1 s, induced emf is:
a) 25 V
b) 50 V
c) 5 V
d) 10 V
Correct answer: b) 50 V
Explanation:
Initial flux = BA = 0.5 × 0.02 = 0.01 Wb
E = N(ΔΦ/Δt) = 500 × (0.01 / 0.1) = 500 × 0.1 = 50 V.
MCQ No. 53
In an RL circuit (L = 4 H, R = 2 Ω), time constant is:
a) 1 s
b) 2 s
c) 4 s
d) 8 s
Correct answer: b) 2 s
Explanation:
τ = L/R = 4 / 2 = 2 s.
MCQ No. 54
If current in an inductor changes from 0 to 10 A in 0.2 s and L = 3 H, induced emf is:
a) 150 V
b) 50 V
c) 30 V
d) 100 V
Correct answer: a) 150 V
Explanation:
E = L(ΔI/Δt) = 3 × (10 / 0.2) = 3 × 50 = 150 V.
MCQ No. 55
A conductor of length 1 m moves with velocity 5 m/s at 60° to magnetic field (B = 0.4 T). Induced emf:
a) 1 V
b) 2 V
c) 0.87 V
d) 1.73 V
Correct answer: d) 1.73 V
Explanation:
E = Bℓv sinθ
= 0.4 × 1 × 5 × sin60°
= 2 × 0.866 ≈ 1.73 V.
MCQ No. 56
If frequency of AC is tripled, inductive reactance becomes:
a) Same
b) Double
c) Triple
d) Nine times
Correct answer: c) Triple
Explanation:
XL = 2πfL. Directly proportional to frequency.
MCQ No. 57
An ideal transformer has 1000 primary turns and 200 secondary turns. If primary voltage is 220 V, secondary voltage is:
a) 44 V
b) 110 V
c) 440 V
d) 22 V
Correct answer: a) 44 V
Explanation:
Vs/Vp = Ns/Np = 200/1000 = 1/5
Vs = 220 × 1/5 = 44 V.
MCQ No. 58
If induced emf in a rotating coil is E = E₀ sinωt, maximum emf occurs when:
a) ωt = 0
b) ωt = 90°
c) ωt = 180°
d) ωt = 270°
Correct answer: b) ωt = 90°
Explanation:
Sinθ maximum at 90°, so emf maximum.
MCQ No. 59
Power loss due to eddy currents can be minimized by using:
a) Solid iron core
b) Thick core
c) Laminated silicon steel core
d) Copper core
Correct answer: c) Laminated silicon steel core
Explanation:
Lamination increases resistance and silicon steel reduces hysteresis loss.
MCQ No. 60
If magnetic flux linked with coil changes sinusoidally, induced emf will:
a) Be constant
b) Be sinusoidal
c) Be zero
d) Be linear
Correct answer: b) Be sinusoidal
Explanation:
Emf ∝ rate of change of flux. Derivative of sinusoidal function is also sinusoidal.
MCQ No. 61
In RL circuit, current reaches 63% of final value after:
a) τ/2
b) τ
c) 2τ
d) 3τ
Correct answer: b) τ
Explanation:
At t = τ (time constant), current reaches 63% of maximum.
MCQ No. 62
The ratio of secondary to primary current in ideal transformer is:
a) Ns/Np
b) Np/Ns
c) Vs/Vp
d) L/R
Correct answer: b) Np/Ns
Explanation:
Ip/Is = Ns/Np → Is/Ip = Np/Ns.
MCQ No. 63
If magnetic field through coil reverses direction completely, flux change equals:
a) Φ
b) 2Φ
c) Φ/2
d) Zero
Correct answer: b) 2Φ
Explanation:
Flux changes from +Φ to –Φ → total change = 2Φ.
MCQ No. 64
Self-inductance increases when:
a) Turns decrease
b) Core removed
c) Permeability increases
d) Resistance increases
Correct answer: c) Permeability increases
Explanation:
L ∝ μ. Higher permeability → greater inductance.
MCQ No. 65
In generator, mechanical energy converts into:
a) Magnetic energy
b) Heat energy
c) Electrical energy
d) Light energy
Correct answer: c) Electrical energy
Explanation:
Generator works on electromagnetic induction converting mechanical energy into electrical energy.
MCQ No. 66
If angular speed of rotating coil doubles, induced emf:
a) Same
b) Double
c) Half
d) Four times
Correct answer: b) Double
Explanation:
E₀ = NBAω. Proportional to angular speed.
MCQ No. 67
Magnetic flux is maximum when angle between B and area vector is:
a) 0°
b) 30°
c) 60°
d) 90°
Correct answer: a) 0°
Explanation:
Φ = BA cosθ. Maximum when cos0° = 1.
MCQ No. 68
If L = 5 H and current decreases at rate 4 A/s, induced emf magnitude is:
a) 20 V
b) 5 V
c) 9 V
d) 1.25 V
Correct answer: a) 20 V
Explanation:
E = L(dI/dt) = 5 × 4 = 20 V.
MCQ No. 69
An AC generator produces peak emf of 100 V. RMS value is:
a) 100 V
b) 50 V
c) 70.7 V
d) 141 V
Correct answer: c) 70.7 V
Explanation:
Erms = E₀ / √2 = 100 / 1.414 ≈ 70.7 V.
MCQ No. 70
If magnetic field increases linearly with time, induced emf is:
a) Increasing
b) Decreasing
c) Constant
d) Zero
Correct answer: c) Constant
Explanation:
Linear change → constant rate of change → constant emf.
MCQ No. 71
In mutual induction, induced emf in secondary depends on:
a) Change in current in primary
b) Resistance of secondary
c) Length of wire
d) Voltage source
Correct answer: a) Change in current in primary
Explanation:
Emf induced due to changing magnetic field produced by primary current.
MCQ No. 72
If coil area doubles, induced emf in rotating coil:
a) Same
b) Double
c) Half
d) Four times
Correct answer: b) Double
Explanation:
E₀ = NBAω. Directly proportional to area.
MCQ No. 73
Direction of induced current always:
a) Supports cause
b) Opposes cause
c) Independent
d) Random
Correct answer: b) Opposes cause
Explanation:
This is Lenz’s Law.
MCQ No. 74
Transformer efficiency is maximum when:
a) Copper loss = Iron loss
b) Copper loss zero
c) Iron loss zero
d) Voltage maximum
Correct answer: a) Copper loss = Iron loss
Explanation:
Maximum efficiency occurs when variable copper loss equals constant iron loss.
MCQ No. 75
If magnetic flux becomes zero, induced emf will be zero only when:
a) Flux is constant zero
b) Flux decreasing
c) Flux increasing
d) Flux oscillating
Correct answer: a) Flux is constant zero
Explanation:
Emf depends on change in flux, not value of flux. If zero and constant → emf zero.
Set–4 (Expert / Conceptual-Tricky Level)
Electromagnetic Induction – MCQs 76–100
MCQ No. 76
A circular loop enters a uniform magnetic field region with constant velocity. The induced current in the loop will:
a) Remain constant
b) Increase continuously
c) Decrease continuously
d) Be non-uniform during entry
Correct answer: d) Be non-uniform during entry
Explanation:
During entry, the area inside the field increases non-linearly (circular geometry), so rate of change of flux is not constant → emf varies.
MCQ No. 77
If magnetic flux through a coil is zero at an instant, induced emf at that instant:
a) Must be zero
b) Must be maximum
c) May or may not be zero
d) Always negative
Correct answer: c) May or may not be zero
Explanation:
Emf depends on rate of change of flux, not on flux value itself.
MCQ No. 78
Two coils are placed close to each other. Mutual inductance depends on:
a) Resistance of coils
b) Relative orientation
c) Applied voltage
d) Current magnitude
Correct answer: b) Relative orientation
Explanation:
Mutual inductance depends on geometry, number of turns, permeability, and relative positioning.
MCQ No. 79
A rectangular loop rotates in uniform magnetic field. When plane of loop is parallel to magnetic field, induced emf is:
a) Zero
b) Maximum
c) Minimum but not zero
d) Half maximum
Correct answer: b) Maximum
Explanation:
Flux = BA cosθ. When plane is parallel, θ = 90°, flux zero but rate of change maximum → emf maximum.
MCQ No. 80
If current in inductor becomes constant, induced emf across it becomes:
a) Maximum
b) Zero
c) Equal to supply
d) Infinite
Correct answer: b) Zero
Explanation:
Emf = L(dI/dt). For constant current, dI/dt = 0.
MCQ No. 81
An AC source is connected to pure inductor. Average power consumed over one cycle is:
a) Maximum
b) Half maximum
c) Zero
d) Infinite
Correct answer: c) Zero
Explanation:
In pure inductive circuit, current lags 90°. Average power over full cycle = 0.
MCQ No. 82
If speed of a magnet falling through a conducting pipe becomes constant, it is due to:
a) Gravity decrease
b) Air resistance
c) Eddy currents producing opposing force
d) Magnetic force disappears
Correct answer: c) Eddy currents producing opposing force
Explanation:
Induced currents oppose motion (Lenz’s law), producing magnetic drag.
MCQ No. 83
A coil has inductance L. If number of turns is doubled, inductance becomes:
a) 2L
b) 4L
c) L/2
d) L²
Correct answer: b) 4L
Explanation:
L ∝ N². Doubling N → inductance becomes 4L.
MCQ No. 84
Energy stored in magnetic field of inductor is supplied by:
a) Magnetic field
b) Electric field
c) External source
d) Core material
Correct answer: c) External source
Explanation:
Work done by power supply is stored as magnetic energy.
MCQ No. 85
A conducting rod moves parallel to magnetic field lines. Induced emf is:
a) Maximum
b) Minimum
c) Zero
d) Infinite
Correct answer: c) Zero
Explanation:
E = Bℓv sinθ. For parallel motion, θ = 0°, sin0 = 0.
MCQ No. 86
If magnetic flux through coil changes as Φ = kt², induced emf varies as:
a) t
b) t²
c) Constant
d) 1/t
Correct answer: a) t
Explanation:
E = dΦ/dt = 2kt → proportional to t.
MCQ No. 87
In transformer, step-up means:
a) Current increases
b) Voltage increases
c) Power increases
d) Resistance increases
Correct answer: b) Voltage increases
Explanation:
Step-up transformer increases voltage while decreasing current.
MCQ No. 88
If frequency of AC supply increases, transformer core losses due to eddy currents:
a) Decrease
b) Increase
c) Remain same
d) Become zero
Correct answer: b) Increase
Explanation:
Eddy current loss ∝ frequency².
MCQ No. 89
An inductor opposes change in:
a) Voltage
b) Current
c) Resistance
d) Power
Correct answer: b) Current
Explanation:
Self-induction opposes change in current.
MCQ No. 90
When a coil is suddenly disconnected from battery, spark is observed because:
a) Current becomes zero instantly
b) Induced emf is very large
c) Resistance decreases
d) Voltage disappears
Correct answer: b) Induced emf is very large
Explanation:
Large dI/dt produces high induced emf across inductor.
MCQ No. 91
RMS value of AC is equal to peak value divided by:
a) 2
b) π
c) √2
d) √3
Correct answer: c) √2
Explanation:
Erms = E₀ / √2.
MCQ No. 92
If coil rotates with constant angular speed in magnetic field, frequency of induced emf depends on:
a) Magnetic field strength
b) Area of coil
c) Angular speed
d) Number of turns
Correct answer: c) Angular speed
Explanation:
f = ω / 2π.
MCQ No. 93
If resistance of secondary increases, ideal transformer secondary voltage:
a) Increases
b) Decreases
c) Remains same
d) Becomes zero
Correct answer: c) Remains same
Explanation:
Voltage ratio depends only on turns ratio in ideal transformer.
MCQ No. 94
Magnetic flux linkage of coil is:
a) Φ
b) N/Φ
c) NΦ
d) Φ/N
Correct answer: c) NΦ
Explanation:
Flux linkage = Number of turns × Flux per turn.
MCQ No. 95
If permeability of core increases 5 times, inductance becomes:
a) Same
b) 5 times
c) 25 times
d) 1/5
Correct answer: b) 5 times
Explanation:
L ∝ μ.
MCQ No. 96
When AC frequency is very high, inductive reactance becomes:
a) Very small
b) Zero
c) Very large
d) Constant
Correct answer: c) Very large
Explanation:
XL = 2πfL. Increases with frequency.
MCQ No. 97
In generator, slip rings are used to:
a) Increase current
b) Reduce resistance
c) Produce AC output
d) Convert AC to DC
Correct answer: c) Produce AC output
Explanation:
Slip rings maintain continuous connection to rotating coil, giving AC output.
MCQ No. 98
If magnetic field changes but coil is open circuit, induced emf:
a) Zero
b) Maximum
c) Exists but no current flows
d) Infinite
Correct answer: c) Exists but no current flows
Explanation:
Emf induced regardless of circuit completion; current requires closed path.
MCQ No. 99
A conducting loop shrinks in uniform magnetic field. Induced current direction is such that magnetic field produced:
a) Aids decrease in area
b) Opposes decrease in flux
c) Is zero
d) Reverses randomly
Correct answer: b) Opposes decrease in flux
Explanation:
By Lenz’s law, induced current opposes change in flux.
MCQ No. 100
If current through inductor varies sinusoidally, voltage across it:
a) In phase
b) 90° behind
c) 90° ahead
d) 180° out of phase
Correct answer: c) 90° ahead
Explanation:
In pure inductor, voltage leads current by 90°.
