Introduction

Magnets can be found in many everyday objects. Refrigerator doors have magnetic strips on them to keep them closed, computers use magnetic disks to store information, credit cards have magnetic strips on the back of them. Even loudspeakers and toasters can have magnets in them.

The two ends or poles of a magnet behave differently. They are called the north pole (N) and the south pole (S) of a magnet.

The two magnets in Fig.1 below are pointing in the same direction. They both have their north poles towards the right.



Drag the left-hand magnet to the right until its north pole approaches the south pole of the other magnet, then let it go.



Drag the magnets around to see if this is always the case.

In the experiment below, the right-hand magnet has been turned around.



Drag the north pole of one magnet near to the north pole of the other, then let it go.



Now bring the south poles near each other. You will have to drag one magnet over the top and past the other one.



In both cases, the

force

A force is a push or a pull. A force can lift an object, change its shape, or accelerate it.force between the poles is called the

magnetic force

The magnetic force is the force that occurs between magnetic objects. The magnetic force can be either attractive or repulsive depending on the two objects.magnetic force.

Around every magnet is a magnetic field. The

magnetic field

Around every magnet there is an invisible magnetic field.magnetic field will have an effect on any other magnet that comes into the field.

The needle of a compass always points along the direction of the magnetic field. Drag the plotting compass in Fig.3 below around the magnet to investigate the field. Observe how the direction of the field changes from point to point.



A common way to show the magnetic field is by drawing field lines or lines of force. The red (north) end of the compass points in the direction of the lines of force.



The magnetic field is strongest where there are most field lines. This occurs near the poles of the magnet.

Boats, aeroplanes, and walkers use compasses to help them know which way to travel in the dark. The red (north) end of the needle on the compass always points towards geographic north. This is because the needle is influenced by the magnetic field of the earth. The place we call the North Pole of the earth is in fact its magnetic south pole.




Magnets also attract non-magnetized objects, such as paper clips, iron filings, and fridge doors. Objects which are attracted to a magnet, but are not themselves magnets, are made of magnetic materials. Iron and steel are two common magnetic materials. Wood, paper, and plastic are not magnetic materials. They are not affected by magnetic fields.



Drinks cans are made of aluminium and are not magnetic. Soup cans and baked bean cans are often made of steel.

How would you decide if a can is made of aluminium?
Why are there often magnets at can recycling centres?

When two magnets are placed near each other, the two magnetic fields interact with each other. By just looking at the field patterns you can often tell whether the force between them will be attractive or repulsive. When the force is attractive, the field lines seem to be reaching from one magnet to the other. When the force is repulsive the field lines bend away from each other.

Summary


The two ends or poles of a magnet behave differently. One is called the north pole and the other is called the south pole.

Opposite or unlike magnetic poles attract each other. Similar or like magnetic poles repel each other.

Around every magnet there is a magnetic field.