Magnetism and Matter for NEET UG
Magnets, the Earth's magnetic field and the way materials respond to magnetism. Learn why iron is attracted strongly, copper hardly at all, and how hard drives store data.
PhysicsClass 1258 MCQs2 lessons10 flashcards2 memory tricks
Practise Magnetism and Matter free
What you'll learn
- Bar magnets and the Earth's magnetism
Treat a bar magnet as a magnetic dipole and describe the Earth's field. - Magnetic materials
Classify materials as dia-, para- or ferromagnetic and explain hysteresis.
Key formulas
| Field on the axis (far) | B = μ₀(2m)/(4πr³) |
|---|---|
| Field on the equator (far) | B = μ₀m/(4πr³) |
| Torque in a field | τ = mB sin θ |
| Potential energy | U = −mB cos θ |
| Susceptibility | χ = M/H |
| Relative permeability | μ_r = 1 + χ |
| Curie's law (paramagnets) | χ ∝ 1/T |
Memory tricks
Diamagnetic materials are weakly repelled (χ small and negative), paramagnetic weakly attracted (χ small and positive), ferromagnetic strongly attracted (χ large and positive).
Above the Curie temperature a ferromagnet becomes paramagnetic. For iron it is about 770 °C.
Try 3 NEET-style questions
Q1. A bar magnet of magnetic moment 0.5 A m² is placed at 30° to a uniform magnetic field of 0.2 T. The torque on it is
- 0.1 N m
- 0.05 N m
- 0.087 N m
- 0.025 N m
Show answer
Answer: (2) 0.05 N m
τ = mB sin θ = 0.5 × 0.2 × sin 30° = 0.1 × 0.5 = 0.05 N m.
Q2. The magnetic susceptibility of a diamagnetic substance is
- small and negative
- small and positive
- large and positive
- infinite
Show answer
Answer: (1) small and negative
Diamagnetic materials are weakly repelled; their magnetisation opposes the field, so χ is small and negative (−1 ≤ χ < 0).
Q3. The magnetic moment of a current-carrying circular loop of area A and current I is
- I A
- I A²
- 2 I A
- I A / μ₀
Show answer
Answer: (1) I A
For a loop of N turns, M = N I A. For one turn, M = I A.
Practise all 58 questions Free · explanations for every option · see where you go wrong