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Magnetism & Electromagnetic Induction

Biot-Savart law, Ampere's law, Faraday's law, AC circuits, and transformers

Key Concepts
  • A moving charge in a magnetic field feels F = qv × B (perpendicular force)
  • Biot–Savart and Ampere's laws give the field due to currents
  • Faraday's law: a changing flux induces an emf (Lenz's law sets its direction)
  • Inductance opposes changes in current; self and mutual inductance
  • AC circuits: reactance, impedance and resonance
Important Formulae
Force on a charge F = qvB sinθ
Field of a long wire B = μ₀I/(2πr)
Field at loop centre B = μ₀I/(2R)
Induced / motional emf emf = −dΦ/dt; emf = BLv
Reactances X_L = ωL; X_C = 1/(ωC)
Resonance frequency ω = 1/√(LC)
Quick Tips
  • Lenz's law is a statement of energy conservation — induced current opposes the change.
  • At resonance X_L = X_C, impedance is minimum and current is maximum.
  • In an ideal transformer V ∝ N (turns ratio).
Sample Practice Questions

  1. The SI unit of magnetic flux is the:

    • tesla
    • weber
    • henry
    • gauss
    Show answer

    Answer: weber

  2. The magnetic force on a charge moving parallel to a magnetic field is:

    • Maximum
    • Zero
    • Perpendicular to velocity
    • Along the field
    Show answer

    Answer: Zero

  3. At resonance in a series LCR circuit, the impedance is:

    • Maximum
    • Minimum
    • Zero
    • Infinite
    Show answer

    Answer: Minimum

  4. Lenz's law is a direct consequence of the conservation of:

    • Charge
    • Momentum
    • Energy
    • Mass
    Show answer

    Answer: Energy

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Practice Questions

Practise randomly selected JEE questions on Magnetism & Electromagnetic Induction. Answers are revealed after each question.

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