Скачать или смотреть Make Your Own Compass at Home With Just a Needle!

You can make a simple compass using just a steel needle and a cork. First, magnetise the needle by stroking it several times in one direction with a permanent magnet, which aligns the magnetic domains inside the steel. Normally, the domains (tiny regions where groups of atomic magnetic dipoles are aligned) point in random directions, cancelling each other out so the needle has little to no net magnetism. Stroking with a magnet forces many of these domains to line up in the same direction, giving the needle an overall north–south magnetic polarity. Then, carefully push the needle through a small cork and float it on the water. Because the cork keeps the needle afloat, the magnetized needle is free to turn, and it will rotate until it aligns with the Earth’s magnetic field, effectively acting as a compass.

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