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Which way does a compass point in an electromagnetic field with one wire?

Scientists say that the direction of a magnetic field is as follows:

Direction of flow

But how can we prove this?

The best way is to use a compass.

Moving a compass around a wire

From above this would look like the following.

Wire and compass from above

If you plot the ends of a compass's needle around a wire that passes through a piece of paper with direct current through it, you will have the circle above and the direction of flow around the wire.

Do this in several places and you can show rings.

Magnetic field rings

And so you would have the following diagram:

Magnetic field rings around a wire

You can do this anywhere along the length of the wire.

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