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Imagine you have a box of the following materials: a large iron nail, several permanent magnets, lots of insulated wire, a D-cell and a switch....

This is actually quite simple. Iron is ferromagnetic (the quintessential ferromagnet in fact); so we can turn the iron nail into a temporary magnet simply by rubbing it in one direction with the permanent magnets. This applied magnetic field will align the atoms in the iron and turn it into a magnet of its own, at least until random vibrations misalign the atoms again.

Better yet, we can turn it into a controllable electromagnet by wrapping the wires around the nail many times, and then connecting the wires to the battery and the switch in a circuit. Now when we flip the switch on, the nail will be magnetic, but when we flip the switch off it will not be.

So, how temporary would you like your magnet to be? Until it wears off by random vibration, or whenever you flip off the switch?

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