Introduction

What this section does

• This is an orientation section, not an examinable one. It recalls from Std XI that a short bar magnet is a magnetic dipole with a dipole moment $m$, that its field can be found at any point on its axial or equatorial line, and that a freely suspended magnet settles along the geographic north–south direction — the property used in a compass and in navigation.
• It also recalls two standing facts: magnetic lines of force are closed curves that run from north to south outside the magnet and south to north inside it, and magnetic monopoles do not exist, because breaking a magnet always produces two complete dipoles.

What the chapter goes on to cover

• The behaviour of a short bar magnet placed in a uniform magnetic field: the torque on it, its magnetic potential energy, and the angular S.H.M. it performs when disturbed.
• The atomic origin of magnetism, and the classification of materials into diamagnetic, paramagnetic and ferromagnetic with their properties and examples.
• Applications: permanent magnets, electromagnets and magnetic shielding.