The region around a magnet

The idea

The region around a magnet in which its force can be detected has a magnetic field; the lines along which iron filings align in this region represent magnetic field lines.

Iron filings and a magnet

Imagine a sheet of paper over a bar magnet. A teacher sprinkles iron filings on the paper and taps it gently.

What do the iron filings do?

• They arrange themselves in a pattern around the magnet
• They stay scattered in the same way
• They all roll towards the edge of the paper

Look at the region

Press Next step to go from the region, to the filings, to the lines.

Filings show the field

A magnet pulls and pushes on things in the space around it. That space is its magnetic field. The filings feel the force of the magnet, so they line up. The lines they make are the field lines.

The region around a magnet in which its force can be detected has a magnetic field. The lines along which iron filings align in this region represent magnetic field lines.

Notes

A magnet has a magnetic field in the region around it where its force can be detected. The lines along which iron filings align represent magnetic field lines.

Check yourself

What is a magnetic field?

Why do iron filings arrange themselves in a pattern near a magnet?

What do the lines along which iron filings align represent?

A compass needle brought near a bar magnet is deflected. What does this tell you?

• The pattern of iron filings on the paper. The filings only show the field lines. The magnetic field is the region around the magnet where its force can be detected.
• The region around a magnet in which its force can be detected — correct. Yes!
• The iron inside the magnet. A magnetic field is a region around the magnet, not a material inside it.
• The air around the magnet pushes them. It is the force of the magnet on the filings that arranges them, not the air.
• The paper under them is tilted. The filings arrange themselves because the magnet exerts a force on them, whichever way the paper is held.
• The magnet exerts a force on them — correct. Yes!
• Magnetic field lines — correct. Yes!
• The edge beyond which the magnet has no effect at all. The lines show the pattern of the magnetic field. They are not a boundary.
• The poles of the magnet. The poles are the two ends of the magnet. The lines of filings represent magnetic field lines.
• The needle is inside the magnet. A compass needle is deflected when it is brought near a bar magnet. It does not have to be inside it.
• The needle is in the magnetic field of the magnet — correct. Yes!
• The magnet is exerting no force on the needle. A deflected needle means the magnet exerts a force on it.