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Magnetism & EMI

Magnetic fields, electromagnetic induction, AC circuits

Key Concepts
  • Magnetic force on charge: F = qv × B (perpendicular to both v and B)
  • Biot-Savart law: magnetic field due to current element
  • Ampere's law: ∮B·dl = μ₀I_enclosed
  • Faraday's law: emf = −dΦ/dt (Lenz's law: induced current opposes change)
  • Self-inductance L: emf = −L dI/dt
Important Formulae
Force on charge in field F = qvB sinθ
Force on current-carrying wire F = BIL sinθ
B due to infinite wire B = μ₀I / (2πr)
B at centre of circular loop B = μ₀I / (2R)
Motional emf emf = BLv
Energy in inductor U = ½LI²
Quick Tips
  • Right-hand rule: curl fingers from v to B; thumb points in direction of F (for +ve charge).
  • Cyclotron: radius r = mv/qB; time period independent of speed.
  • Mutual inductance M: emf₂ = −M dI₁/dt; transformers use mutual induction.
Sample Practice Questions

  1. RMS value of AC voltage V = V₀ sinωt is:

    • V₀
    • V₀/2
    • V₀/√2
    • V₀√2
    Show answer

    Answer: V₀/√2

  2. Eddy currents are reduced by:

    • Increasing current
    • Using solid iron core
    • Laminating the core
    • Increasing frequency
    Show answer

    Answer: Laminating the core

  3. Force on a current-carrying conductor of length L in magnetic field B at angle θ:

    • BIL cosθ
    • BIL sinθ
    • BIL
    • BL sinθ
    Show answer

    Answer: BIL sinθ

  4. Lorentz force on a charge q moving with velocity v in field B:

    • qvB
    • qv × B
    • qE + qvB
    • qE only
    Show answer

    Answer: qv × B

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Practice Questions

Practice 20 randomly selected NEET questions on Magnetism & EMI. Answers are revealed after each question.

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