It works by sliding a wiper terminal across a resistive material, typically a thin film or chunk of carbon or a resistive wire ... to a potentiometer, but handles more power. See resistor.

Moving the position of the slider on this resistor, changes the length of wire in the circuit which changes the resistance. A variable resistor is used in some dimmer switches and volume controls.

1m length of constantan wire, a metre rule, a low voltage power pack, a variable resistor, a voltmeter, an ammeter, connecting leads, a switch, 2 crocodile clips, Sellotape. The temperature of the ...