Magnets and poles
A magnet is a material that attracts magnetic materials such as iron, steel, nickel and cobalt. Every magnet has two poles: a north pole (N) and a south pole (S). When a magnet hangs freely, its north pole always points towards the Earth's geographic north, which is how a compass works.
The law of poles
Like poles repel and unlike poles attract. When you bring two north poles together they push apart; a north pole and a south pole pull together.
Key idea
Like poles repel (N–N or S–S). Unlike poles attract (N–S). The region around a magnet where its force acts is the magnetic field, drawn as field lines from N to S.
Magnetic field
The space around a magnet where a magnetic force can be felt is called the magnetic field. We can show it using iron filings or a plotting compass. Field lines are closest together near the poles, where the field is strongest.
Electromagnet
An electromagnet is made by winding a coil of wire around an iron core and passing a current through it. It is magnetic only while the current flows, and its strength increases with more turns of wire, a larger current, or a soft iron core.
Example
Electromagnets are used in electric bells, cranes that lift scrap metal, and loudspeakers, because they can be switched on and off.
Remember
- Unlike poles attract; like poles repel.
- A freely hanging magnet points north–south.
- An electromagnet works only while current flows and can be switched off.