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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 cylindrical around the wire.

Memory aids

The right hand grip 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 curved fingers show the direction of the magnetic field around the wire.

For those without right hands, an alternative left hand grip rule can be used with the thumb pointing in the direction of electron flow (opposite to conventional current). The fingers of the left hand curving around the wire will be pointing in the direction of the magnetic field.


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.