Permanent & Induced Magnets

Permanent Magnets

A permanent magnet is an object that produces its own persistent magnetic field without the need for an external power source. It always has a magnetic field around it, which can attract magnetic materials like iron.

Common examples include:

• Bar magnets
• Horseshoe magnets
• Refrigerator magnets

Permanent magnets are usually made from materials such as steel or iron alloys that can be magnetised and retain their magnetism.

The magnetic field lines around a permanent magnet:

• Exit from the north pole and enter the south pole
• Form continuous loops outside and inside the magnet
• Are closer together where the magnetic field is stronger, usually near the poles

For instance, the field lines around a bar magnet curve from the north pole to the south pole, showing the direction of the magnetic force.

Example: Visualising magnetic field lines

If you sprinkle iron filings around a bar magnet, the filings align along the magnetic field lines, revealing the pattern of the magnetic field. This shows the strongest field near the poles where the filings cluster more densely.

Induced Magnets

An induced magnet is a piece of magnetic material that becomes a magnet only when placed in a magnetic field. This process is called magnetic induction.

When a magnetic material like iron is near a permanent magnet, the magnetic field causes the domains inside the material to align temporarily, turning it into a magnet.

This induced magnetism is usually temporary. The material loses its magnetism once it is removed from the magnetic field.

The magnetic field of the induced magnet interacts with the original magnet’s field, often strengthening the overall magnetic effect.

For instance, if you bring a paperclip close to a strong permanent magnet, the paperclip becomes temporarily magnetised and can attract small iron objects like pins.

Example: Induced magnetism in a paperclip

If you bring a paperclip close to a strong permanent magnet, the paperclip becomes temporarily magnetised and can attract small iron objects like pins. Once you move the paperclip away, it quickly loses its magnetism.

Magnetic Domains

Magnetic materials are made up of tiny regions called magnetic domains. Each domain contains many atoms with magnetic moments aligned in the same direction.

In an unmagnetised piece of iron, the domains are randomly oriented, so their magnetic effects cancel out.

In a permanent magnet, most domains are aligned in the same direction, producing a strong overall magnetic field.

In an induced magnet, the domains align temporarily when exposed to a magnetic field but return to random orientations once the field is removed.

Example: Domain alignment in a permanent magnet

When a piece of steel is magnetised, the magnetic domains inside rotate so that their magnetic fields point in the same direction, creating a strong, lasting magnetic field.

Magnetic Forces Between Magnets

Magnets exert forces on each other that can either be attractive or repulsive:

• Opposite poles (north and south) attract
• Like poles (north-north or south-south) repel

When a magnet induces magnetism in a magnetic material, the induced magnet will have poles arranged so that it is attracted to the original magnet.

This is why a magnetic material near a magnet is always pulled towards it, never pushed away.

Example: Force between two bar magnets

If you bring the north pole of one bar magnet close to the south pole of another, they attract and stick together. If you try to push two north poles together, they repel and push apart.