A bar magnet is equivalent to which of the following?

The correct answer is Option (2) → A solenoid

Option (1) A toroid — Incorrect. The field of a toroid is confined to the space inside its windings and is zero outside. So, unlike a bar magnet, it has no north and south pole and no net magnetic moment.

Option (2) A solenoid — Correct. The field lines of a bar magnet and of a current-carrying solenoid look alike. They leave one end, enter the other and run on through the inside. A bar magnet can be thought of as a large number of circulating currents, like the turns of a solenoid. Cutting it in half gives two smaller solenoids.

Option (3) A straight current-carrying wire — Incorrect. The field lines of a straight wire are circles around the wire. They have no ends at which north and south poles could appear.

NCERT (2026-27):
Bar Magnet as an Equivalent Solenoid – “The resemblance of magnetic field lines for a bar magnet and a solenoid suggest that a bar magnet may be thought of as a large number of circulating currents in analogy with a solenoid.”