When a magnet is broken in half, how does it become two separate magnets?

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Offline thedoc

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Tim harvey asked the Naked Scientists:

If you break a magnet in half, it becomes two separate magnets, right. So how does it "know" it has been broken?. What causes it to physically change? Where does it get the energy to do this?

What would happen if you broke a magnet in two in outer space where earth gravity had no effect?

What do you think?
« Last Edit: 03/10/2016 23:13:05 by chris »


Offline chris

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Hi Tim

The reason this happens is that the starting magnet (before it broke into two) actually consists of many tiny magnets all aligned. These are actually called "magnetic dipoles" and they arise from the spin of the electrons in the iron particles that make up the magnet. In a permanent magnet, the orientation of the particles, and hence the dipoles, are locked into position by the crystal structure, which is what enables the magnet to hold on to its magnetisation.

When you break the magnet in half, because the magnetic dipoles in each of the two halves remain aligned as they were previously, they still generate a field as before, albeit a smaller one.

Therefore the Earth's magnetic field has no influence in this situation, and hence breaking the magnet in space would produce an identical result.
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Offline evan_au

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Quote from: Tim Harvey
What would happen if you broke a magnet in two in outer space where earth gravity had no effect?
Magnetism arises from the electromagnetic force.

In ferromagnetism like the permanent magnet you discuss, the electromagnetic force is far more powerful than their gravitational force (and this is a general comment on the relative strengths of Gravity and Electromagnetism).

So Earth's gravitational field (or its absence) has no impact on the magnetic field of a permanent magnet (or its shattered fragments).