Magnetism & Magnetic Materials JEE Main Guide

Magnetism and magnetic materials blends the macroscopic behavior of magnets with the microscopic origin of magnetic properties in matter. JEE Main draws one to two questions from this chapter per session, with conceptual questions about the classification of magnetic materials being particularly common. The chapter is compact and rewards focused revision.

Magnetic Dipoles and Bar Magnets

A bar magnet is a magnetic dipole with a north and south pole separated by a small distance. The magnetic field on the axial line and equatorial line have specific magnitudes and directions that JEE Main tests directly. On the axial line, the field points in the same direction as the dipole moment; on the equatorial line, it points in the opposite direction and is half the magnitude at the same distance.

When a magnetic dipole is placed in a uniform external field, it experiences a torque that tends to align it with the field. The potential energy is minimum when aligned and maximum when anti-aligned. These dipole-in-field results closely parallel the electric dipole results — connect with our electrostatics guide to leverage those parallels.

Earth's Magnetism

Earth behaves like a giant magnetic dipole. The key quantities are: magnetic declination, magnetic dip or inclination, and the horizontal component of Earth's field. The total field, horizontal component, and vertical component form a right triangle related by the dip angle. JEE Main tests numerical problems using these relationships. The dip is 0 degrees at the magnetic equator and 90 degrees at the magnetic poles. Take a free mock test on magnetism to practice these calculations.

Classification of Magnetic Materials

Diamagnetic materials are weakly repelled by magnetic fields; their induced magnetization opposes the external field. Examples include bismuth, copper, and water. Paramagnetic materials are weakly attracted; examples include aluminum and platinum. Ferromagnetic materials are strongly attracted and can be permanently magnetized; examples include iron, nickel, and cobalt.

The susceptibility is small and negative for diamagnetic, small and positive for paramagnetic, and large and positive for ferromagnetic materials. The relative permeability is less than 1 for diamagnetic, slightly greater than 1 for paramagnetic, and much greater than 1 for ferromagnetic. These comparisons are frequently tested in JEE Main in table-matching or true/false formats.

Hysteresis and the B-H Curve

Ferromagnetic materials exhibit hysteresis: when the magnetizing field is cycled, magnetization lags behind the field. Key features: the retentivity (magnetization remaining when H is removed), the coercivity (reverse field needed to demagnetize), and the area of the loop (proportional to energy dissipated per cycle). Hard magnetic materials have high coercivity — used for permanent magnets. Soft magnetic materials have low coercivity — used for transformer cores. The distinction between hard and soft magnetic materials and their applications is a standard JEE conceptual question.

Revision Strategy

Master the bar magnet field formulas, Earth's magnetism trigonometry, the three material classifications with their susceptibility signs, and the hysteresis loop features. This chapter pairs naturally with our magnetic effects guide. Follow our physics score strategy and upgrade for ₹149/month to access our full question bank.