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
-
Ampere's circuital law: ∮B·dl = :
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Answer: μ₀ × enclosed current
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Magnetic field at the centre of a circular loop of radius R carrying current I:
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Answer: μ₀I/2R
-
An AC generator works on the principle of:
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Answer: Electromagnetic induction
-
The SI unit of magnetic flux is:
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Answer: Weber (Wb)
Practice Questions
Practice 20 randomly selected NEET questions on Magnetism & EMI. Answers are revealed after each question.
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What are the key concepts in Magnetism & EMI for NEET?
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.
Which formulae are important for Magnetism & EMI in NEET?
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.
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