A freely suspended bar magnet always comes to rest in which direction?

When a bar magnet is suspended freely, for example from a thread tied at its middle, so that it can rotate in a horizontal plane, it always comes to rest pointing in the geographical north-south direction. The end that points towards the north is called the north-seeking pole or north pole of the magnet, and the other end is the south pole.

This happens because the Earth itself behaves like a giant magnet. The Earth's magnetic field is believed to be produced by the movement of molten iron and nickel in its outer core, a process called the geodynamo. The magnetic field lines of the Earth run roughly from the geographic south to the geographic north. Since unlike poles attract, the north pole of the suspended magnet is attracted towards the Earth's magnetic pole near the geographic North Pole. This means that the Earth's magnetic pole near the geographic North Pole is actually a magnetic south pole.

The Earth's magnetic poles do not coincide exactly with its geographic poles. The angle between the geographic meridian and the magnetic meridian at a place is called the angle of declination. The angle that the Earth's magnetic field makes with the horizontal is called the angle of dip or inclination; it is 90° at the magnetic poles and 0° at the magnetic equator.

This property of magnets was used to make the magnetic compass, which was used for navigation by sailors. The compass is believed to have been developed first in China, around the 11th century. A compass needle is a small, light magnet that can rotate freely on a pivot.

Some animals, such as migratory birds, sea turtles and some bacteria, also use the Earth's magnetic field to find their direction.

Why not the other options?

• ✗East-West is perpendicular to the direction in which a free magnet rests.
• ✗North-East to South-West is incorrect.
• ✗Any direction is incorrect; a free magnet always aligns along the north-south line.