Magnetism

Property of Magnets

• We say that unlike poles attract, and like poles repel.

Magnetic field• Magnets create

magnetic fields.

• These cannot be seen.

• They are the space around a magnet over which it has a magnetic effect.

Distinguish between:

a magnet

a magnetic material

a non magnetic material?

Produces a magnetic field

Reacts to a magnetic field

Doesn’t react to a magnetic field

To investigate the magnetic field of a magnet and plot it.

• Small compasses called plotting compasses can be used to show the magnetic field around a bar magnet

• When plotting compasses are put around a bar magnet, the needles point away from the magnet's north pole and towards its south pole.

To investigate the magnetic field of a magnet and plot it

• Put a plotting compass on the north pole of the magnet• With a pencil mark the positions of both ends of the needle of the plotting compass• Move the compass so that the south pole on the compass is now at the point

where the north pole was.• Continue this until you reach the south pole.• Join the dots

weakest field further away from poles

N S

Strength of a magnetic field

strongest field

at poles

strongest field

at poles

The magnetic field of a bar magnet

NNS S

Magnetic field pattern: N poles together

What do you notice about the pattern of the lines of force in the region between the two north poles?

The earths magnetic fieldThe Earth does not contain a giant bar magnet, but it

behaves as if it does.

The Earth has a magnetic pole in the north and one in the south.

.

How a compass works• The small magnet inside a compass feels

the earths magnetic force and always points toward the south magnetic pole of the earth ( but we call it the north pole!)

Uses of magnetsThe Maglev Trains in Japan use magnetic repulsion to train to “float” above the track

Magnets used to sort metal in a ship yard

Orienteering

• A magnetic compass helps us in direction finding.

• Compasses always points towards north pole ( but this is actually the south magnetic pole )

Do you know…1. How magnets behave when they come into contact

with each other

2. What a magnetic field is

3. How to plot the magnetic field of a magnet

4. How a compass works

5. Some uses of magnetic fields