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Cheat sheet · NEET Preparation Physics

Magnetism and Matter cheat sheet

The whole chapter on one page: key formulas, facts and the points to remember, for quick revision before a test.

NEET · Physics

Cheat sheet

Class 12 · Chapter 5Magnetism and Matter

Dia repels weakly, Para attracts weakly, Ferro attracts strongly.

1. Bar Magnet

Baxial=μ04π2mr3B_{axial} = \dfrac{\mu_0}{4\pi}\dfrac{2m}{r^3}Beq=μ04πmr3B_{eq} = \dfrac{\mu_0}{4\pi}\dfrac{m}{r^3}
τ=mBsin⁡θ\tau = mB\sin\thetaU=−mBcos⁡θU = -mB\cos\theta

Gauss's law for magnetism: net flux through a closed surface = 0 (no monopoles).

2. Magnetic Materials

Typeχ (susceptibility)BehaviourExample
Diamagneticsmall, negativeweakly repelledBi, Cu, water
Paramagneticsmall, positiveweakly attractedAl, Na, O₂
Ferromagneticlarge, positivestrongly attractedFe, Ni, Co

B=μ0(H+M)B = \mu_0(H + M), μr=1+χ\mu_r = 1 + \chi. Curie law: χ∝1T\chi \propto \dfrac1T (paramagnets).

3. Hysteresis

  • Retentivity: B left when H = 0.
  • Coercivity: reverse H to make B = 0.
  • Soft iron (low coercivity) for electromagnets; steel for permanent magnets.

4. Key Points

  • Ferromagnets become paramagnetic above Curie temperature.
  • Earth's field: declination, dip.
  • Superconductors are perfect diamagnets.
  • Magnetic field lines form closed loops.

Remember: Bar magnet field | dia, para, ferro | hysteresis

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