Magnets and magnetic fields · Year 3
A magnet has two poles, north and south. Like poles repel and unlike poles attract. Magnets attract only a few materials – iron, steel, nickel and cobalt – and their pull acts through paper, plastic and even your hand. Earth itself is a giant magnet, which is why a compass works.
Key facts
- Like poles repel; unlike poles attract.
- Magnetic materials: iron, steel, nickel, cobalt. Most metals (copper, aluminium, gold) are not magnetic.
- Magnetic field lines go from north to south outside a magnet; closer lines mean a stronger field.
- The field is strongest at the poles and gets weaker with distance.
- A compass needle is a small magnet; its north pole points to Earth’s geographic North (where there is a magnetic south pole).
- Induced magnets are only magnetic near a permanent magnet; heating or hammering destroys magnetism.
Worked examples
Example 1
A magnet’s field is 80 mT at 2 cm and falls as 1/(distance²). What is it at 8 cm?
Answer: 5 mT