Signedon bulb: GENERAL ELECTRIC / (GE logo) . 100 W - 120 V
painted on switch: CENTRAL SCIENTIFIC CO. / (missing) CENCO U.S.A. / LABORATORY APPARATUS
Inscribedon socket: 660 W
FunctionThe bimetal thermal switch of an electrical appliance is a way of controlling at which temperatures it is to be turned on and off. It consists of two strips of different metals attached to each other. Since different metals expand by different amounts, a strip of two metals that is straight at one temperature will curl in one direction or another as the temperature changes. If one uses the strip of metal as part of an electric circuit, it will work as a temperature-sensitive switch as by curling in different directions it can be put in contact with different circuits.
In this demonstrational setup, a lightbulb is placed in proximity of the strip, and as a result, the bulb wil turn on and off intermittently. As the strip cools, it curls to be in contact with the switch that closes the circuit turning the lightbulb on. Then, as it is heated by the bulb, the strip moves away from the circuit, turning the bulb off.