Concept of Magnetism

A magnet is a material that produces a magnetic field and can attract magnetic substances such as iron, nickel, cobalt, and some of their alloys.

The region around a magnet in which it can exert a magnetic force is called its magnetic field.

A common permanent magnet is a bar magnet. It has two ends called magnetic poles:

• North-seeking pole (N-pole): The end that points approximately towards geographic north when the magnet is freely suspended.
• South-seeking pole (S-pole): The end that points approximately towards geographic south.

Important observations

• Like poles repel each other: N repels N and S repels S.
• Unlike poles attract each other: N attracts S.
• A freely suspended bar magnet settles approximately along the geographic north–south direction.

Magnetic field lines are imaginary lines used to represent the magnetic field around a magnet.

Rules for magnetic field lines

• Outside a bar magnet, field lines emerge from the north pole and enter the south pole.
• Inside the magnet, they travel from the south pole to the north pole.
• Therefore, magnetic field lines form continuous closed loops.
• Field lines never intersect each other.
• Where field lines are closer together, the magnetic field is stronger.
• The field is strongest near the poles of a magnet.

• Suppose a bar magnet is cut into two pieces.
• Each piece becomes a smaller magnet with its own north pole and south pole.

Thus, cutting a magnet does not produce an isolated north pole or an isolated south pole. In ordinary magnets, poles always occur in pairs. Isolated magnetic poles, called magnetic monopoles, have not been observed in ordinary magnetic materials.

• A compass needle is a small magnet mounted so that it can rotate freely.
• Earth produces its own magnetic field. Therefore, the compass needle experiences a turning effect and aligns itself with Earth’s magnetic field.
• This is why the needle points approximately in the north–south direction.

Real-life connection: Navigation

Before GPS, sailors, travellers, and surveyors used a compass for direction. A compass works because its magnetic needle aligns with Earth’s magnetic field.

In 1600, the English scientist William Gilbert gave a scientific explanation for the north–south alignment of a freely suspended magnet. He concluded that Earth behaves approximately like a huge magnet.

Earth’s magnetic field is similar in pattern to the field of a bar magnet. In the school-level model, Earth is treated as if a large bar magnet were placed inside it.

Key idea

The north pole of a freely suspended magnet points toward geographic north. Since unlike poles attract, the region near geographic north must behave like a magnetic south pole.

Similarly, the region near geographic south behaves like a magnetic north pole.

The Earth’s magnetic field is approximately directed from geographic south to geographic north.

• Ancient peoples knew of natural magnetic ore, including in the region historically associated with Magnesia in Greece.
• William Gilbert systematically investigated magnetism and proposed that Earth behaves like a magnet.
• In 1820, Hans Christian Oersted showed that electric current produces a magnetic effect.
• Later work by Ampere, Biot, Savart, and Maxwell established the close relationship between electricity and magnetism.

• Every ordinary magnet has two poles: north and south.
• Like poles repel; unlike poles attract.
• A freely suspended magnet aligns approximately along the north–south direction.
• Magnetic field lines are closed loops.
• A broken magnet always produces smaller magnets, each with both poles.
• Earth behaves approximately like a giant magnet.
• Near geographic north lies Earth’s magnetic-south region in the simple bar-magnet model.
• A compass works because its needle aligns with Earth’s magnetic field.