What is a Thermostats A device which automatically regulates temperature. regulates temperature.regulates temperature. Thermostats activates different devices when their temperature reaches a particular point. Bimetallic Strip This strip is made of two strips of different metals (brass and iron). The two strips of metals normally riveted together. When heat is apply both metals expand. Brass expands more. When expand the strips will curve with the brass on the outside. When the strips cools, the metals will go back to their original length. Thermostat in Electric Iron The thermostat is used to keep the iron at a particular temperature. When the strip is straight, it forms part of an electric circuit. Current will now flows through the circuit. Iron will now warms up. When the iron gets hotter than the required temperature, the strip will bend away from the contact. The circuit will break and the heater turned off. As the bimetallic strip cools, it straighten. Forming the circuit again. Current will flow and heater turns on again. Screwing the control knob in and out will regulate the temperature at which the heater switch on. Gas Thermostat Gas thermostat normally regulates the temperature in a gas oven. Gas thermostat has a rod made of invar. Invar expand slightly when heated. As the ovens temperature increases, the brass tube expands. The invar rod is attached to the brass tube. It will move to the left. The valve is then pulled closer. This will reduce the flow of gas to the burner. As the brass cools, the rod moves, opening the valve and increase the flow of gas again. The control knob can used to alter the position of the valve and so control the steady temperature of the oven.