Magnetism
ICSE Class 6 · Physics · Chapter 6
What this chapter covers
- Magnetic and non-magnetic substances
- Properties of a magnet
- Magnetic field around a magnet
- Making magnets: permanent and temporary
- Electromagnets
- Care, storage and demagnetisation
Key points
- A magnet attracts iron, nickel, cobalt and steel. These are magnetic substances.
- Wood, glass, plastic, rubber and many metals such as copper and aluminium are non-magnetic.
- Every magnet has two poles, north and south, where its pull is strongest.
- A freely suspended magnet always rests in the north and south direction.
- Like poles repel; unlike poles attract.
- The magnetic field is the space around a magnet where its pull is felt. Iron filings show it as curved lines.
- The Earth behaves like a giant magnet. A compass uses this to show directions.
- Magnets can be made by induction, by stroking and by using electricity.
- Permanent magnets, usually of steel, keep their magnetism. Temporary magnets, usually of soft iron, lose it quickly.
- An electromagnet is a coil of wire around a soft iron core that works only while current flows. Its strength can be changed.
- Heating, hammering and a changing electric current can demagnetise a magnet.
- Store magnets in pairs with unlike poles side by side and keepers across the ends.
Questions answered
Name three magnetic substances and three non-magnetic substances.
Magnetic: iron, nickel and cobalt (steel also works). Non-magnetic: wood, glass and plastic (copper, aluminium and rubber also work).
What are the poles of a magnet?
The poles are the two places near the ends of a magnet where its pull is strongest. They are called the north pole and the south pole.
A bar magnet hangs freely from a thread. In which direction will it come to rest?
It comes to rest pointing north and south. Its north pole points towards the geographic north.
The north pole of one magnet is brought near the north pole of another. What happens?
The two magnets push each other away, because like poles repel.
How can you see the magnetic field around a bar magnet?
Cover the magnet with paper, sprinkle iron filings on it and tap gently. The filings form curved lines from one pole to the other.
Why does a compass needle always point north and south?
The Earth behaves like a huge magnet. The needle is a small magnet that lines up with the Earth's magnetic field.
Give one difference between a permanent magnet and a temporary magnet.
A permanent magnet keeps its magnetism for a long time. A temporary magnet loses its magnetism soon after it is taken away from a magnet.
Why is soft iron, and not steel, used as the core of the electromagnet in a scrapyard crane?
Soft iron loses its magnetism as soon as the current is switched off, so the scrap drops when the operator wants it to. Steel would stay a magnet and keep holding the scrap.