Physics — Electromagnetism for the NEET Exam

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 non-symmetric charge distributions
• !Kirchhoff's junction rule sign errors — currents entering a node are positive, leaving are negative (or vice versa, but the convention must be consistent)
• !Confusing capacitor charging vs discharging time constants (τ = RC for both, but voltage changes in opposite directions)
• !Misidentifying the direction of induced current using Lenz's law — forgetting that induced current opposes the change in flux, not the flux itself
• !Mixing up the force on a current-carrying conductor (F = BIL sin θ) with the force on a moving charge (F = qvB sin θ)

Study tips

• 1For circuits, master Kirchhoff's two laws: KCL (sum of currents at any node = 0) and KVL (sum of voltages around any closed loop = 0). These are the foundation of all NEET circuit problems.
• 2Drill Gauss's law for the three NEET-tested geometries: spherical shell, infinite line charge, infinite plane. Know the E-field formula for each.
• 3Memorise the combination of resistors (series and parallel) and capacitors (series and parallel) — the rules are opposite for R vs C and this swap is a common NEET trap.
• 4Practice Faraday's law numericals: EMF = −dΦ/dt = −N × d(BA)/dt. Know how to calculate flux for a rectangular coil rotating in a magnetic field.
• 5For magnetic effects (Biot-Savart, Ampere's law), focus on the finite and infinite straight wire results — these are the most-tested NEET geometries.

Sample NEET Physics — Electromagnetism questions

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

1. 1

   A parallel plate capacitor has plate area A and separation d. Its capacitance is:

   • Aε₀Ad
   • Bε₀A/dCorrect
   • Cε₀d/A
   • Dd/(ε₀A)
   Why this answer?

   The capacitance of a parallel plate capacitor (with vacuum between the plates) is C = ε₀A/d, where A is the plate area, d is the separation, and ε₀ = 8.854 × 10⁻¹² F/m. Inserting a dielectric of constant K gives C = Kε₀A/d.

2. 2

   Two resistors of 4 Ω and 6 Ω are connected in parallel. The equivalent resistance is:

   • A10 Ω
   • B2.4 ΩCorrect
   • C5 Ω
   • D24 Ω
   Why this answer?

   1/R_eq = 1/4 + 1/6 = 3/12 + 2/12 = 5/12. R_eq = 12/5 = 2.4 Ω. Note: parallel resistance is always less than the smallest individual resistance.

3. 3

   According to Lenz's law, the induced current in a coil acts to:

   • AEnhance the change in magnetic flux that caused it
   • BOppose the change in magnetic flux that caused itCorrect
   • CMaintain the current magnetic flux constant
   • DReverse the direction of the applied magnetic field
   Why this answer?

   Lenz's law states that the induced EMF (and hence the induced current) is in a direction such that it opposes the change in magnetic flux that produced it. This is consistent with energy conservation — it takes work to move a magnet against the opposing force.