Physics — Electromagnetism for the JEE Main Exam — Indian candidates

Common failure modes

These are the patterns that cause most candidates to lose marks on this topic. Recognising them in advance is half the work.

• !Applying Gauss's law to asymmetric charge distributions where it does not simplify the integral
• !Wrong sign convention in Faraday's law (forgetting the minus sign, or misidentifying the "positive normal" direction)
• !Confusing electric field lines with equipotential surfaces — they are always perpendicular
• !Misapplying superposition: forgetting to vector-add field contributions from multiple sources
• !Treating magnetic flux through a loop incorrectly when the loop is tilted relative to the field

Study tips

• 1Drill Gauss's law for the five standard geometries (sphere, infinite line, infinite plane, cylindrical shell, spherical shell) until the result is immediate.
• 2Use Lenz's law as a sanity check after every induction calculation — the induced current must oppose the change that caused it.
• 3Memorise the Biot-Savart law result for a long straight wire and a circular loop; JEE Advanced builds composite-geometry problems from these.
• 4For capacitors: practice energy stored, charge redistribution when plates move, and dielectric insertion in a single multi-step problem.
• 5Sketch field lines and equipotentials for every E&M setup — it forces conceptual clarity before algebra.
• 6For candidates in India, JEE Main test windows are typically denser in the spring; book test centres in metro cities (Delhi, Mumbai, Bengaluru, Chennai, Kolkata) early to secure preferred dates.

Sample JEE Main Physics — Electromagnetism questions

These sample items mirror the format and difficulty of real JEE Main questions. Practice with thousands more on the free Koydo question bank.

1. 1

   A charge Q is enclosed in a spherical shell. According to Gauss's law, the electric flux through the shell is:

   • AQ / ε₀Correct
   • BQ / (4πε₀)
   • CQ / (4πε₀R²)
   • D4πR²Q / ε₀
   Why this answer?

   Illustrative JEE-style: Gauss's law states ∮E·dA = Q_enc / ε₀. The total flux through any closed surface enclosing charge Q is Q / ε₀, independent of the shape or size of the surface.

2. 2

   A magnetic flux through a coil changes from 5 Wb to 2 Wb in 0.1 s. The magnitude of the induced EMF is:

   • A0.3 V
   • B3 V
   • C30 VCorrect
   • D300 V
   Why this answer?

   Illustrative JEE-style: By Faraday's law, |EMF| = |ΔΦ/Δt| = |5 − 2| / 0.1 = 30 V for a single-turn coil.

3. 3

   Two parallel infinite plates with surface charge densities +σ and −σ face each other. The electric field between the plates is:

   • Aσ / ε₀Correct
   • Bσ / (2ε₀)
   • C2σ / ε₀
   • Dzero
   Why this answer?

   Illustrative JEE-style: Each plate contributes σ / (2ε₀). Between opposite plates the fields add (both point in the same direction), giving E = σ / ε₀. Outside the plates the fields cancel.

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