Class 12 Physics Chapter 5 Magnetism and Matter – Revision Notes

A bar magnet behaves like a pair of magnetic poles, and this Class 12 Physics Chapter 5 summary traces that idea through axial and equatorial field formulas, Earth’s own magnetism, and how different materials classify by their response to a field.

Last Updated: September 23, 2026

Bar Magnet

• Magnetic moment: m=q_m×2l.
• Axial field: B=(μ₀/4π)(2m/r³); Equatorial: B=(μ₀/4π)(m/r³).
• Torque τ=mB sinθ; PE U=−mB cosθ.

Earth’s Magnetism

• Declination, dip/inclination, horizontal component B_H=B cos(dip).

Material Classification

• Diamagnetic: χ<0, weakly repelled (e.g. bismuth).
• Paramagnetic: χ>0 small, weakly attracted (e.g. aluminium); Curie’s law χ∝1/T.
• Ferromagnetic: large χ>0, strongly attracted, hysteresis (e.g. iron).

One-Line Summary

A bar magnet behaves as an equivalent solenoid producing dipole-like fields; materials are classified as diamagnetic, paramagnetic, or ferromagnetic based on their magnetic susceptibility.

Quick visual: a worked diagram from the full Solutions page, for reference.

Frequently Asked Questions

What are the three types of magnetic materials described in this chapter?
Materials are classified as diamagnetic (weakly repelled), paramagnetic (weakly attracted), and ferromagnetic (strongly attracted and capable of retaining magnetism), based on how their atomic magnetic moments respond to an external field.

How is the Earth modeled as a magnet in this chapter?
The Earth behaves approximately like a giant bar magnet tilted at an angle to its rotational axis, which explains the existence of magnetic declination and magnetic inclination at different locations on the surface.

Written by Satish

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