How much of JEE Main comes from Electromagnetic Induction and AC?

JEEGenie estimates about 5% of JEE Main marks come from Electromagnetic Induction and AC, based on recent papers. The share varies from year to year.

Which formulas matter most in Electromagnetic Induction and AC?

The Electromagnetic Induction and AC sheet on this page has 23 formula entries, starting with Magnetic Flux, Faraday's Law of Electromagnetic Induction, Lenz's Law, Motional EMF, Eddy Currents. Each one comes with when to use it and the trap to avoid.

What topics does Electromagnetic Induction and AC cover for JEE?

Electromagnetic Induction and AC covers Faraday's Law, Lenz's Law, Self and Mutual Inductance, AC Circuits, LCR Circuits and Resonance, Transformers.

How should I revise Electromagnetic Induction and AC before the exam?

Learn each formula together with its condition of use, read the trap listed beside it, then practise questions and review every mistake. The practice link on this page opens Electromagnetic Induction and AC questions on JEEGenie.

How many previous-year questions are there on Electromagnetic Induction and AC?

JEEGenie has 473 previous-year questions on Electromagnetic Induction and AC, and this page shows a few with worked explanations.

Is practice on Electromagnetic Induction and AC free on JEEGenie?

Sign-up is free and includes a 7-day Pro trial. After the trial, free accounts keep a limited daily quota.

Electromagnetic Induction and AC for JEE Main & Advanced — formulas, what is asked, and traps

JEEGenie estimates about 5% of JEE Main marks come from Electromagnetic Induction and AC. This page covers 23 formula entries, each with when to use it, what JEE asks and the traps. A common slip: Forgetting the negative sign indicates Lenz's law direction.

Key points to know

Magnetic Flux. Magnetic flux through a surface is the total magnetic field passing perpendicularly through it.
Faraday's Law of Electromagnetic Induction. The induced EMF in a closed loop equals the negative rate of change of magnetic flux through the loop.
Lenz's Law. The induced current opposes the change in magnetic flux that produces it.
Self-Inductance. Self-inductance is the property of a coil to oppose changes in current through it by inducing an EMF.
Mutual Inductance. Mutual inductance quantifies the EMF induced in one coil due to current change in another coil.
AC Current and Voltage. Alternating current varies sinusoidally with time, characterized by amplitude, frequency, and phase.
Reactance and Impedance. Reactance is the opposition to AC due to inductance or capacitance; impedance is total opposition.
Transformer. A transformer transfers electrical energy between circuits via mutual induction, changing voltage and current levels.
Eddy Current Braking. Eddy currents induced in a moving conductor produce a opposing force, used for braking.
Inductive and Capacitive Reactance. Inductive reactance increases with frequency; capacitive reactance decreases with frequency.

Formula sheet

Name	Formula	When to use
Magnetic Flux	$Φ_{B} = \int \vec{B} \cdot d \vec{A} = B A \cos θ$	Use to quantify magnetic field linkage in Faraday's law or to compute induced EMF.
Faraday's Law of Electromagnetic Induction	$E = - \frac{d Φ_{B}}{d t}$	Use to find induced EMF whenever magnetic flux through a circuit changes with time.
Lenz's Law	$E = - \frac{d Φ_{B}}{d t}$ (negative sign embodies Lenz's law)	Use to determine the direction of induced current or EMF.
Motional EMF	$E = B l v$ (for a rod of length l moving perpendicular to B with speed v)	Use when a conductor moves through a constant magnetic field, e.g., sliding rod on rails.
Eddy Currents	No simple formula; use Lenz's law and $E = - d Φ / d t$ for loops	Use to explain damping in galvanometers, induction furnaces, or magnetic braking.
Self-Inductance	$E_{L} = - L \frac{d i}{d t}$ , $L = \frac{N Φ_{B}}{i}$	Use to analyze RL circuits, energy stored in inductors, or back EMF.
Inductance of a Solenoid	$L = μ_{0} n^{2} A l = μ_{0} \frac{N^{2}}{l} A$ (for air core)	Use to compute L of a solenoid given its dimensions and turns.
Mutual Inductance	$E_{2} = - M \frac{d i_{1}}{d t}$ , $M = \frac{N_{2} Φ_{21}}{i_{1}}$	Use to analyze transformers or coupled circuits.
Energy Stored in an Inductor	$U = \frac{1}{2} L i^{2}$	Use to find energy in an inductor in DC or AC circuits.
AC Current and Voltage	$i (t) = I_{0} \sin (ω t + ϕ)$ , $v (t) = V_{0} \sin (ω t + ϕ)$	Use to describe any sinusoidal AC source or signal.
RMS Value	$I_{rms} = \frac{I_{0}}{\sqrt{2}}$ , $V_{rms} = \frac{V_{0}}{\sqrt{2}}$ (for sine wave)	Use to compute power or compare AC with DC.
Reactance and Impedance	$X_{L} = ω L$ , $X_{C} = \frac{1}{ω C}$ , $Z = \sqrt{R^{2} + (X_{L} - X_{C})^{2}}$	Use to analyze any series RLC circuit.
Resonance in Series RLC Circuit	$ω_{0} = \frac{1}{\sqrt{L C}}$ , $f_{0} = \frac{1}{2 π \sqrt{L C}}$	Use to find resonant frequency or analyze tuning circuits.
Power in AC Circuits	$P_{avg} = V_{rms} I_{rms} \cos ϕ$	Use to compute power consumed in any AC circuit.
Transformer	$\frac{V_{s}}{V_{p}} = \frac{N_{s}}{N_{p}} = \frac{I_{p}}{I_{s}}$ (ideal, no losses)	Use to step up or step down AC voltage in power transmission.
Solving RL Circuit Transients	$i (t) = \frac{V}{R} (1 - e^{- t / τ})$ (charging), $i (t) = I_{0} e^{- t / τ}$ (discharging), $τ = L / R$	Use to find current or voltage in RL circuits during switching.
Phasor Diagrams	$V = V_{0} ∠ ϕ$ , $I = I_{0} ∠ θ$	Use to visualize phase relationships and add voltages/currents in AC circuits.
Quality Factor (Q-factor)	$Q = \frac{ω_{0} L}{R} = \frac{1}{R} \sqrt{\frac{L}{C}}$	Use to characterize resonance in RLC circuits.
Eddy Current Braking	$F \propto v$ (for low speeds), no simple formula	Use to explain magnetic braking in trains or roller coasters.
Finding Induced EMF in a Rotating Coil	$E = N B A ω \sin (ω t)$ (for N turns, area A, angular speed ω)	Use to analyze AC generators or dynamos.
Average EMF in Half Cycle	$E_{avg} = \frac{2}{π} N B A ω$ (for half cycle)	Use to find average EMF in AC generators over half rotation.
Inductive and Capacitive Reactance	$X_{L} = ω L$ , $X_{C} = \frac{1}{ω C}$	Use to find impedance or phase in AC circuits.
Power Factor Correction	$\cos ϕ = \frac{R}{Z}$ , correction capacitor $C = \frac{P (\tan ϕ_{1} - \tan ϕ_{2})}{ω V^{2}}$	Use to improve efficiency in AC power systems.

Open the Electromagnetic Induction and AC formula page

What JEE asks

Magnetic Flux. JEE often asks flux through a rotating coil or a loop in a non-uniform field, requiring integration.
Faraday's Law of Electromagnetic Induction. JEE tests with moving rods, rotating coils, or time-varying B fields; often requires differentiation.
Lenz's Law. JEE asks to find direction of induced current in a loop near a moving magnet or changing current.
Motional EMF. JEE often combines with circuits: find current, force, or power in a moving rod.
Eddy Currents. JEE asks applications like energy loss in transformers or damping in moving coil meters.
Self-Inductance. JEE often asks L of a solenoid or toroid, or behavior in AC circuits.
Inductance of a Solenoid. JEE gives solenoid parameters and asks L or energy stored.
Mutual Inductance. JEE may ask M between coaxial solenoids or in a transformer.
Energy Stored in an Inductor. JEE may ask energy in an RL circuit at a given time or during transients.
AC Current and Voltage. JEE often gives AC source parameters and asks RMS, peak, or average values.
RMS Value. JEE asks RMS of complex waveforms or in power calculations.
Reactance and Impedance. JEE often asks to find Z, current, or phase angle in RLC circuits.
Resonance in Series RLC Circuit. JEE asks resonant frequency, current at resonance, or Q-factor.
Power in AC Circuits. JEE asks power factor, power consumed, or condition for maximum power.
Transformer. JEE asks turns ratio, efficiency, or applications like power transmission.
Solving RL Circuit Transients. JEE asks current at a given time or energy stored after a long time.
Phasor Diagrams. JEE may ask to draw phasor diagram for RLC or find resultant voltage.
Quality Factor (Q-factor). JEE asks Q-factor from given L, C, R or bandwidth.
Eddy Current Braking. JEE may ask qualitative or numerical problems on eddy current braking.
Finding Induced EMF in a Rotating Coil. JEE asks peak EMF, average EMF, or EMF at a given angle.
Average EMF in Half Cycle. JEE may ask average EMF in a given time interval.
Inductive and Capacitive Reactance. JEE asks how reactance changes with frequency or find values.
Power Factor Correction. JEE may ask to find capacitor value for desired power factor.

Common traps

Forgetting that flux depends on the angle between B and area vector, not just B and area. Magnetic Flux
Forgetting the negative sign indicates Lenz's law direction. Faraday's Law of Electromagnetic Induction
Thinking induced current opposes the flux itself, not the change in flux. Lenz's Law
Forgetting that v, B, and l must be mutually perpendicular; otherwise use $E = B l v \sin θ$ . Motional EMF
Thinking eddy currents only occur in ferromagnetic materials; they occur in any conductor. Eddy Currents
Forgetting that L depends only on geometry (turns, area, length) and core material, not on current. Self-Inductance
Using n (turns per unit length) vs N (total turns); formula uses n or N correctly. Inductance of a Solenoid
Assuming M is symmetric ( $M_{12} = M_{21}$ ) always true for linear media. Mutual Inductance
Thinking energy is stored only while current is changing; $U = \frac{1}{2} L i^{2}$ is stored whenever $i \neq 0$ , including steady state, and depends on the instantaneous current, not on $d i / d t$ . Energy Stored in an Inductor
Confusing peak value with RMS value; RMS = peak/√2 for sine wave. AC Current and Voltage
Using RMS formula for non-sinusoidal waveforms; it's different. RMS Value
Forgetting that $X_{L}$ and $X_{C}$ depend on frequency; at resonance, $X_{L} = X_{C}$ . Reactance and Impedance
Forgetting that resonance condition is $X_{L} = X_{C}$ , not $X_{L} = R$ . Resonance in Series RLC Circuit
Forgetting that $\cos ϕ$ is power factor; for pure L or C, $\cos ϕ = 0$ . Power in AC Circuits

Topics in Electromagnetic Induction and AC

Faraday's Law
Lenz's Law
Self and Mutual Inductance
AC Circuits
LCR Circuits and Resonance
Transformers

Previous-year questions on Electromagnetic Induction and AC

JEEGenie has 473 previous-year questions on Electromagnetic Induction and AC. A few worked examples follow.

Year	Questions
2026	30
2025	21
2024	45
2023	51
2022	48
2021	59
2020	24
2019	33
2018	11
2017	12
2016	9
2015	6
2014	8
2013	16
2012	6
2011	7
2010	6
2009	3
2008	1
2007	2
2006	14
2005	7
2004	12
2003	5
2002	8
2001	2
2000	2
1999	4
1998	2
1997	3
1996	2
1995	1
1994	2
1993	2
1991	1
1989	1
1988	1
1986	1
1985	1
1983	1
1982	1
1981	1
1979	1

Question 1 hard

When a coil is placed in a time dependent magnetic field the power dissipated in it is

P

. The number of turns, area of the coil and radius of the coil wire are

N

A

and

r

respectively. For a second coil number of turns, area of the coil and radius of the coil wire are

2 N

2 A

and

3 r

respectively. When the first coil is replaced with second coil the power dissipated in it is

\sqrt{2} α P

. The value of

α

is ______.

36
128 $\sqrt{2}$
16
64

Answer: A

Explanation. For induced EMF in a coil,

E \propto N A

since the magnetic field changes at the same rate. Resistance of the coil wire: Length of wire

\propto N \times (circumference) \propto N \sqrt{A}

, cross-sectional area of wire

\propto r^{2}

, so

R \propto \frac{N \sqrt{A}}{r^{2}} .

Power dissipated:

P = \frac{E^{2}}{R} \propto \frac{(N A)^{2}}{N \sqrt{A} / r^{2}} = \frac{N^{2} A^{2} r^{2}}{N \sqrt{A}} = N A^{3 / 2} r^{2} .

For the second coil:

N^{'} = 2 N, A^{'} = 2 A, r^{'} = 3 r .

Thus

P^{'} \propto (2 N) (2 A)^{3 / 2} (3 r)^{2} = 2 N \cdot (2^{3 / 2} A^{3 / 2}) \cdot 9 r^{2} = 2 \cdot 2^{3 / 2} \cdot 9 N A^{3 / 2} r^{2} = 36 \sqrt{2} P .

Given

P^{'} = \sqrt{2} α P

\sqrt{2} α = 36 \sqrt{2} ⟹ α = 36.

36

Option A.

From NTA/IIT papers: JEE Main 2026 · 2 Apr Shift 1

Question 2 easy

An electric bulb rated as

100 W - 220 V

is connected to an ac source of rms voltage 220 V. The peak value of current through the bulb is :

0.32 A
0.64 A
0.45 A
2.2 A

Answer: B

Explanation. The bulb’s resistance is constant:

R = \frac{V_{rms}^{2}}{P} = \frac{220^{2}}{100} = 484 Ω

. RMS current:

I_{rms} = \frac{V_{rms}}{R} = \frac{220}{484} = \frac{5}{11} \approx 0.4545 A

. Peak current:

I_{0} = I_{rms} \sqrt{2} = \frac{5}{11} \times 1.414 \approx 0.643 A

. Thus peak current is

0.64 A

. Answer is option B.

From NTA/IIT papers: JEE Main 2025 · 3 Apr Shift 2

Question 3 medium

A alternating current at any instant is given by

i = [6 + \sqrt{56} \sin (100 π t + π / 3)]

A. The

r m s

value of the current is ______ A.

Answer: 8

Explanation. The current is given by

i = 6 + \sqrt{56} \sin (100 π t + π / 3)

A. This is a mixed (DC + AC) current. The rms value of such a current is:

i_{r m s} = \sqrt{I_{d c}^{2} + I_{a c, r m s}^{2}}

where

I_{d c} = 6

A and

I_{0} = \sqrt{56}

A (peak AC component). The rms of the AC part:

I_{a c, r m s} = \frac{I_{0}}{\sqrt{2}} = \frac{\sqrt{56}}{\sqrt{2}} = \sqrt{28}

Therefore:

i_{r m s} = \sqrt{(6)^{2} + (\sqrt{28})^{2}} = \sqrt{36 + 28} = \sqrt{64} = 8 A

From NTA/IIT papers: JEE Main 2024 · 4 Apr Shift 1

Question 4 medium

The induced emf can be produced in a coil by A. moving the coil with uniform speed inside uniform magnetic field B. moving the coil with non uniform speed inside uniform magnetic field C. rotating the coil inside the uniform magnetic field D. changing the area of the coil inside the uniform magnetic field Choose the correct answer from the options given below:

A and C only
C and D only
B and D only
B and C only

Answer: B

Explanation. The induced emf in a coil is given by Faraday’s law:

E = - \frac{d Φ}{d t}

where

Φ = \int \vec{B} \cdot d \vec{A}

is the magnetic flux through the coil. For emf to be induced, the magnetic flux through the coil must change with time. **Option A: Moving the coil with uniform speed inside a uniform magnetic field** If the coil moves with uniform speed entirely inside a uniform magnetic field, the magnetic field

\vec{B}

is constant, and the area

A

and orientation of the coil remain unchanged. Therefore, the flux

Φ = B A \cos θ

remains constant, so

\frac{d Φ}{d t} = 0

No emf is induced. So A is incorrect. **Option B: Moving the coil with non-uniform speed inside a uniform magnetic field** Even if the speed is non-uniform, as long as the coil remains entirely inside the uniform magnetic field and its area and orientation do not change, the flux remains constant. Acceleration or changing speed does not change flux if the coil stays fully within the same uniform field. So B is incorrect. **Option C: Rotating the coil inside the uniform magnetic field** When the coil rotates, the angle

θ

between the magnetic field and the area vector changes with time. Thus,

Φ = B A \cos θ (t)

changes with time, so

\frac{d Φ}{d t} \neq 0

An emf is induced. So C is correct. **Option D: Changing the area of the coil inside the uniform magnetic field** If the area

A

changes with time while

\vec{B}

is uniform, then

Φ = B A (t) \cos θ

changes with time, so

\frac{d Φ}{d t} \neq 0

An emf is induced. So D is correct. Thus, the correct statements are **C and D only**. Answer: (B)

From NTA/IIT papers: JEE Main 2023 · 6 Apr Shift 1

Frequently asked questions

How much of JEE Main comes from Electromagnetic Induction and AC?: JEEGenie estimates about 5% of JEE Main marks come from Electromagnetic Induction and AC, based on recent papers. The share varies from year to year.
Which formulas matter most in Electromagnetic Induction and AC?: The Electromagnetic Induction and AC sheet on this page has 23 formula entries, starting with Magnetic Flux, Faraday's Law of Electromagnetic Induction, Lenz's Law, Motional EMF, Eddy Currents. Each one comes with when to use it and the trap to avoid.
What topics does Electromagnetic Induction and AC cover for JEE?: Electromagnetic Induction and AC covers Faraday's Law, Lenz's Law, Self and Mutual Inductance, AC Circuits, LCR Circuits and Resonance, Transformers.
How should I revise Electromagnetic Induction and AC before the exam?: Learn each formula together with its condition of use, read the trap listed beside it, then practise questions and review every mistake. The practice link on this page opens Electromagnetic Induction and AC questions on JEEGenie.
How many previous-year questions are there on Electromagnetic Induction and AC?: JEEGenie has 473 previous-year questions on Electromagnetic Induction and AC, and this page shows a few with worked explanations.
Is practice on Electromagnetic Induction and AC free on JEEGenie?: Sign-up is free and includes a 7-day Pro trial. After the trial, free accounts keep a limited daily quota.