Magnetisation and Induced Magnetism
Simple Explanation
Magnetisation is the process of turning an unmagnetized magnetic material into a magnet, by aligning its internal domains. This can be done by stroking it repeatedly with an existing magnet, or by placing it inside a strong magnetic field (such as inside a coil carrying an electric current). Induced magnetism happens when a magnetic material becomes temporarily magnetized just by being brought NEAR a magnet — even without touching it — and loses this induced magnetism again once the magnet is taken away.
Why Do We Need It?
Induced magnetism explains why a magnet can pick up an unmagnetized paperclip, which can then pick up ANOTHER paperclip — the first paperclip itself becomes a temporary induced magnet while it stays near the original magnet.
Worked Example
Explain a "chain" of paperclips picked up by a magnet
A strong magnet picks up an iron paperclip, and a second paperclip then sticks to the bottom of the first one, forming a short chain. Explain how the second paperclip is held in place.
Why Does This Work?
A strong external magnetic field can temporarily align the domains inside a nearby magnetic material, even without physical contact — this alignment (and the resulting induced magnetism) only persists while the external field remains strong enough nearby, which is why it disappears when the magnet is taken away.
Real-Life Example
Demagnetizing a screwdriver
A magnetized steel screwdriver (useful for holding small screws) can be demagnetized by heating it strongly, or by hitting it repeatedly with a hammer.
Both heat and mechanical shock disturb the aligned domains inside the screwdriver, scrambling them back toward random orientations and removing its magnetism.
Practice
A paperclip is held near (but not touching) a strong magnet and becomes weakly magnetic. What is this an example of?
MediumCommon mistake
Assuming induced magnetism is permanent — it is temporary, and disappears once the magnetic material is moved away from the inducing magnet's field.
Quick Review
- Magnetisation: stroking with a magnet, or placing in a strong field, aligns domains permanently (for hard materials).
- Induced magnetism: temporary magnetism from being near a magnet, without contact.
- Demagnetisation: heat or mechanical shock disturbs aligned domains, removing magnetism.