Center For Integrating Research and Learning

ArrowMagnets from Mini to Mighty

Temporary Magnets: When is a Magnet Not a Magnet?

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Though permanent magnets can last a long time, they fall short in the power department. Scientists measure magnetic strength in units called tesla and gauss; one tesla equals 10,000 gauss. Your fridge magnet is a modest 10 gauss. The Earth's magnetic field is about .5 gauss (or 0.00005 tesla). The most powerful permanent magnets available produce fields about 1.5 tesla. While that’s hardly shabby – magnets of that strength are used in MRI machines – it’s still pretty limiting for many scientific and other applications. Theoretically you could make more powerful permanent magnets, but with all that metal in it, it would be extraordinarily heavy and impractical.

Luckily, there’s more than one way to make a magnet. Take electromagnets: They aren’t permanent, but they can be far stronger than the strongest permanent magnet.

PHYSICS FACTOID: Naturally occurring magnets were formed when lightning struck magnetite on Earth.

But before we get to the really heavy stuff, let’s start with other, smaller types of temporary magnets.

Click here to open a new window and see a random smattering of soft iron filings. (Iron nails or paper clips would also do the trick here).

Nothing special about these filings. Pretty hum-drum.

Now click the “on” button to expose these filings to a magnetic field and see what happens.

Presto-chango! Now that they’re in a magnetic field, these filings have themselves become magnets. Just like the piece of iron you saw in the previous section. Except that these filings won’t retain the property in the absence of a field. The second you take the magnet away, they’re demoted again from miniscule magnets to run-of-the-mill iron filings. Easy come, easy go. Soft iron and other types of iron alloys behave this way. That’s why they are used as temporary magnets in telephones and electric motors.

Electric Motor

Let’s move on to a type of temporary magnet that can flex some more muscle.

Next Page ArrowElectromagnets: Two Forces Team Up

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