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Electromagnetism

Demonstration: Electromagnetic field

A rechargeable spotlight was used to pass a large current (~17 amps) along a wire which was held next to a compass.

When the spotlight was turned on the compass needle moved at right angles to the wire, showing the current has a magnetic field.

Positioning the wire above and below the compass showed the shape of the magnetic field to be cylidrical around the wire.

The right hand rule was mentioned as being an easy way to work out the direction of the magnetic field – the thumb points in the direction of conventional current, the fingers show the direction of the magnetic field produced by the wire.

The left hand rule can also be used – if fingers of the left hand are placed around a wire so that the thumb points in the direction of electron flow (opposite to conventional current), the fingers will be pointing in the direction of the magnetic field produced by the wire.

Extra

Van de Graaff picture page.

Charged candle flame: A candle flame has a charge, and is deflected by the magnetic field of a high-voltage current-carrying wire.