JEE Main Physics · EMI & AC PYQ
JEE Main EMI & AC Previous Year Questions (2002–2026)
Electromagnetic Induction & AC is a P1 Electromagnetism-block chapter with ~6% JEE Main weightage and 1–2 questions per session. Numerical-heavy and pattern-repetitive: RLC circuit problems recur almost every paper with variations in given quantities.
EMI & AC PYQs from 2002 to 2026, spanning Faraday's/Lenz's laws, self- and mutual- induction, LC oscillations, series LCR circuits, resonance and transformers. Each solution includes phasor diagrams where useful.
Electromagnetic Induction & AC at a Glance
Try 5 Real Electromagnetic Induction & AC PYQs
5 real JEE Main questions on Electromagnetic Induction & AC, straight from past papers. Try them, then check the answer.
- Q1JEE Main 2026 (Online) 22nd January Morning Shift
$X P Q Y$ is a vertical smooth long loop having a total resistance $R$ where $P X$ is parallel to $Q Y$ and separation between them is $l$. A constant magnetic field $B$ perpendicular to the plane of the loop exists in the entire space. A rod $C D$ of length $L(L>l)$ and mass $m$ is made to slide down from rest under the gravity as shown in figure. The terminal speed acquired by the rod is $\_\_\_\_$ $\mathrm{m} / \mathrm{s} .(\mathrm{g}=$ acceleration due to gravity)
$\frac{m \mathrm{~g} R}{B^2 l^2}$
$\frac{2 m g R}{B^2 L^2}$
$\frac{2 m g R}{B^2 l^2}$
$\frac{8 m g R}{B^2 l^2}$
- Q2JEE Main 2026 (Online) 21st January Evening Shift
A capacitor C is first charged fully with potential difference of $V_0$ and disconnected from the battery. The charged capacitor is connected across an inductor having inductance L. In $t$ s, 25% of the initial energy in the capacitor is transferred to the inductor. The value of $t$ is ________ s.
$\frac{\pi \sqrt{LC}}{3}$
$\frac{\pi \sqrt{LC}}{2}$
$\pi \sqrt{\frac{LC}{2}}$
$\frac{\pi \sqrt{LC}}{6}$
- Q3JEE Main 2025 (Online) 29th January Morning Shift
A coil of area A and N turns is rotating with angular velocity $\omega$ in a uniform magnetic field $\vec{B}$ about an axis perpendicular to $\vec{B}$. Magnetic flux $\varphi$ and induced emf $\varepsilon$ across it, at an instant when $\vec{B}$ is parallel to the plane of coil, are :
Ï = AB, Ï = NABÏ
Ï = AB, Ï = 0
Ï = 0, ε = 0
Ï = 0, ε = NABÏ
- Q4JEE Main 2025 (Online) 7th April Evening ShiftAn inductor of reactance $100 \Omega$, a capacitor of reactance $50 \Omega$, and a resistor of resistance $50 \Omega$ are connected in series with an AC source of 10 V, 50 Hz. Average power dissipated by the circuit is ___________ W.
- Q5JEE Main 2024 (Online) 29th January Evening Shift
A horizontal straight wire 5 m long extending from east to west falling freely at right angle to horizontal component of earths magnetic field $0.60 \times 10^{-4} \mathrm{~Wbm}^{-2}$. The instantaneous value of emf induced in the wire when its velocity is $10 \mathrm{~ms}^{-1}$ is _________ $\times 10^{-3} \mathrm{~V}$.
Practise the full Electromagnetic Induction & AC set
Every past-paper question of this chapter, with solutions, timing and your accuracy tracked.
Key Sub-Topics & What's Tested
Faraday's & Lenz's Laws
Induced EMF ε = -dΦ/dt, motional EMF ε = Bvl, direction of induced current, energy conservation in induction.
Self-Induction
Inductance L, induced EMF ε = -L(dI/dt), energy stored in inductor U = ½LI², self-inductance of solenoid.
Mutual Induction
M = N₂Φ₂/I₁, transformer principle, coefficient of coupling k, flux linkage between two coils.
LC Oscillations
Energy oscillation between L and C, angular frequency ω = 1/√(LC), analogy with SHM.
AC Fundamentals
RMS vs peak, peak-to-peak, phase angle, average power over a cycle.
AC Through R, L, C
Pure resistor (in phase), pure inductor (current lags voltage by π/2), pure capacitor (current leads by π/2), impedance definition.
Series LCR Circuit
Impedance Z = √(R² + (X_L - X_C)²), phase angle tan φ = (X_L - X_C)/R, resonance at ω = 1/√(LC).
Power in AC Circuits
Average power P = V_rms I_rms cos φ, power factor, quality factor Q = ωL/R = 1/(ωRC) at resonance.
Transformers
Step-up vs step-down, voltage ratio = turns ratio, ideal vs real transformer efficiency, eddy current losses.
Question Type Distribution
| Question Type | Share (approx) | Example Pattern |
|---|---|---|
| Induced EMF Calculation | 25% | Rod of length l moves with velocity v in uniform field B — find induced EMF and current direction. |
| Self/Mutual Inductance | 15% | Find mutual inductance between two coaxial solenoids of lengths l₁, l₂ and turns N₁, N₂. |
| LCR Impedance & Resonance | 25% | Series LCR with R=100Ω, L=0.5H, C=5μF, f=50Hz — find impedance and current. |
| Phasor Diagram / Phase Angle | 15% | In series LCR, current leads voltage by 45°. Find X_L - X_C in terms of R. |
| AC Power / Power Factor | 10% | Calculate power consumed in a circuit with cos φ = 0.6 and V_rms = 100 V, I_rms = 5 A. |
| Transformer Problems | 10% | Ideal transformer with N₁=200, N₂=50 — find output current if input is 2 A. |
How to Solve Electromagnetic Induction & AC PYQs
- 1Build the phasor diagram for every LCR problem. Draw V_R, V_L, V_C as vectors in the complex plane. Resultant magnitude and phase follow geometrically.
- 2Resonance = X_L = X_C. At resonance, ω = 1/√(LC), impedance is purely resistive (Z = R), current is maximum, power factor = 1. Know these facts cold.
- 3Use peak and RMS conversions correctly. V_rms = V₀/√2 = 0.707 V₀. I_rms = I₀/√2. Power formulas use RMS, amplitude formulas use peak.
- 4Motional EMF direction: Fleming's right-hand rule. Thumb = velocity direction, index finger = B direction, middle finger = induced current direction.
- 5LC oscillation period: T = 2π√(LC). Same form as pendulum T = 2π√(l/g) — SHM analogy helps intuition.
- 6Transformer efficiency = (output power / input power) × 100%. Ideal = 100%, real ~95%. Losses from hysteresis, eddy current, copper loss.
Common Mistakes That Cost Marks
- Wrong sign in Faraday's law. ε = -dΦ/dt. The negative sign (Lenz's law) is essential — indicates induced current opposes change in flux.
- Using peak values in power formula. P = V_rms I_rms cos φ, not V₀ I₀ cos φ. Peak values give power off by a factor of 2.
- Confusing X_L and X_C formulas. X_L = ωL (increases with frequency). X_C = 1/(ωC) (decreases with frequency). Swap these and the resonance logic breaks.
- Forgetting power factor in AC power problems. P ≠ VI in AC (unlike DC). Always multiply by cos φ for average power.
- Missing the -L(dI/dt) sign in self-induction. Induced EMF opposes change in current — self-induction is a back-EMF.
Related JEE Main Practice
Frequently asked questions
How many EMI & AC PYQs should I solve?
Target 70–90 PYQs across 2010–2026. LCR circuit templates recur heavily, so focused practice builds instant pattern recognition for resonance and impedance problems.
Are phasor diagrams required for JEE Main?
Yes — for series LCR problems especially. Phasor diagrams handle phase angle calculations in 3 lines what algebra takes 10.
What's the resonance frequency formula I must know?
ω = 1/√(LC), so f = 1/(2π√(LC)). At resonance, X_L = X_C, so inductive and capacitive reactances cancel. Impedance equals R.
How does Lenz's law connect to energy conservation?
Lenz's law states induced current opposes change in flux. This ensures induced current does negative work against external force — energy is conserved (not created).
What's the most-tested EMI & AC PYQ pattern?
Series LCR impedance + phase angle calculation. Appears 2–3 times per 10-year window in different variants (given R, L, C, f → find Z, I, V_R, V_L, V_C).
Why doesn't a pure inductor dissipate power?
In a pure inductor, current lags voltage by π/2, so cos φ = 0. Average power P = VI cos φ = 0. Energy oscillates between inductor's magnetic field and source — no net dissipation.
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