1Seeing the field
Sprinkle iron filings round a magnet and tap the card. Each bit of iron becomes a tiny magnet and turns to line up with the magnetic field.
magnetic field
Lesson 27.2 notes
Magnetic fields
The invisible field around a magnet: iron filings, plotting compasses and field lines.
2Plotting compasses
Put a small plotting compass by the magnet, mark where its needle points, move the compass on and repeat. Join up the dots and you have a field line.
plotting compass
3Field lines
Field lines go from the north pole round to the south pole. They never cross, and they are closest together near the poles, where the field is strongest.
field lines
4Strong and weak
Where the lines are close together the field is strong; where they spread out it is weak. A compass swings round hard near a pole, but only gently far away.
5Attracting magnets
Between a north pole and a south pole, the field lines run straight across the gap from N to S, and the magnets pull together.
6Repelling magnets
Between two north poles, the field lines bend away from each other. Halfway between, the two fields cancel out, so the magnets don't turn a compass there at all.
7Inside a compass
A compass needle is a tiny magnet on a pivot. Its north end is pushed away from a north pole and pulled towards a south pole, so it lines up with the field.
Explore: Field lab
Drag the compass round the magnet and watch its needle follow the field. Then add a second magnet and flip it.
Common mistake: The field is between the lines too
Field lines are a drawing of an invisible field. The field fills all the space round the magnet; the lines show which way it points, and how close they are shows how strong it is.
Remember
- A magnetic field is the region round a magnet where it pushes or pulls on magnetic things.
- A plotting compass lines up with the field: its north end points along the field line.
- Field lines go from north to south, never cross, and are closest together at the poles, where the field is strongest.
Going further at GCSE