The Reach of a Magnet
Induced magnetism — the nail that becomes a magnet
What this lesson covers
Why it matters
Hold a magnet near a plain iron nail, and the nail itself starts picking up paperclips — a magnet by association. Pull the magnet away and the nail forgets everything.
The idea in plain words
Magnetism by influence. Tap the terms.
induction precedes attraction
Why does a magnet attract an UNmagnetised nail at all?
Every 'magnet picks up iron' event is induced magnetism at work
- the effect: induced magnetism — a magnetic material becomes a magnet in a nearby field — nearer end gets the OPPOSITE pole
- the quick learner: soft iron — magnetises strongly, forgets instantly — electromagnet cores, chains of clips
- the long memory: steel — magnetises reluctantly but REMEMBERS — permanent magnets, compass needles
- The near end of the nail is induced with the opposite pole
- Opposite poles attract — induction first, attraction second
Predict first
A paperclip hangs from a magnet, and a SECOND clip hangs from the first. The first clip holds the second because it…
The magnet INDUCES magnetism in clip one, which induces it in clip two — a chain of temporary magnets, alive only while the field is near.
- has become a temporary (induced) magnet itself — correct
- is sticky
- is glued by static electricity
What you do
Bring the magnet close and grow a paperclip chain — then pull it away and watch the chain forget.
Check yourself
The SURE test of whether a bar is a magnet is…
A magnet attracts plain iron AND other magnets — but it can only be REPELLED by another magnet.
Electromagnet cores use soft iron rather than steel because soft iron…
An on/off magnet needs a forgetful core; steel's memory would jam the OFF switch.
Breaking a bar magnet in half gives…
Poles always come in pairs — chop forever and every fragment keeps both.
- repulsion — only two magnets can repel — correct
- attraction
- weighing it
- loses its magnetism the instant the field is removed — correct
- is cheaper
- is harder
- two smaller complete magnets, each with N and S — correct
- a separate N piece and S piece
- two dead pieces of iron