Purpose:Demonstrate thermal expansion of a wire by an electric current, and to apply this to a working model of an ammeter and a voltmeter.
Description:A thin wire is stretched horizontally on a scale. One end of a vertical wire is connected to the horizontal wire, and the other end is looped around a pulley and to a spring, which is connected to a fixed point. A voltage is applied to the horizontal wire. The wire expands and spring pulls down the vertical wire, rotating the pulley and the pointer attached to the pulley, thus indicating the current in the horizontal wire.