Magnets
- Every magnet has a north pole and a south pole. Like poles repel; unlike (opposite) poles attract.
- Magnetic materials are attracted to magnets: iron, nickel, cobalt and steel (which contains iron). Copper, aluminium, gold, plastic and wood are not magnetic.
- Magnetism is a non-contact force.
Magnetic fields
- A magnetic field is the area around a magnet where magnetic materials feel a force.
- Field lines go from the north pole to the south pole. The closer together the lines, the stronger the field, so the field is strongest at the poles.
- You can see the field pattern with iron filings or map it with a plotting compass.
- The Earth has a magnetic field, like a giant bar magnet. A compass needle is a small magnet that lines up with it, pointing north.
Electromagnets
- A current in a wire makes a magnetic field around it. Coiling the wire into a solenoid makes the field stronger; putting an iron core inside makes it stronger still.
- An electromagnet can be switched on and off, and its strength can be changed.
- It gets stronger with more turns of wire, a bigger current, or an iron core.
- Uses: cranes that lift scrap iron, electric bells, door locks, loudspeakers, relays and MRI scanners.
Investigating electromagnets
- Count how many paperclips the electromagnet picks up.
- Independent variable: the number of turns (or the current). Dependent variable: the number of paperclips. Control variables: the core, the wire and the size of the paperclips.
- Plot the results on a graph and describe the pattern: more turns pick up more paperclips.
Key terms
- Magnet
- An object that attracts magnetic materials and has a north and a south pole.
- North pole
- The end of a magnet that points north.
- Attract
- Pull together.
- Repel
- Push apart.
- Magnetic material
- A material attracted to a magnet, such as iron, nickel or cobalt.
- Magnetic field
- The area around a magnet where magnetic materials feel a force.
- Field lines
- Lines that show the shape and direction of a magnetic field.
- Compass
- A small magnet that lines up with a magnetic field.
- Electromagnet
- A magnet made by passing a current through a coil of wire.
- Solenoid
- A coil of wire that makes a magnetic field when a current flows.
- Core
- The iron bar inside an electromagnet that makes it stronger.
- Permanent magnet
- A magnet that always has its own magnetic field.