1. 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.

2. 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.

3.  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.

4. 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.

5.  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.

6.  Screwing the control knob in and out will regulate the temperature at which the heater switch on.

7. 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.

8.  As the oven’s 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.

9.  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.