We use a thermal switch everyday. The thermal switch is also referred to as a temperature switch or a thermostat. It is used to control temperature. It is used by us everyday in our kettles when we boil our water, in our cooker when we are cooking something, in our hotplates when we are frying something and of course in our refrigerators.
The thermal switch or temperature switch utilizes a tungsten strip that is very sensitive to heat. This piece of metal is calibrated to stand various degree of heat. All the user had to do is to set the control knob to the desired temperature. Since this strip of metal found in between the terminals of the switch is heat sensitive, it will contract and expand accordingly. When it reaches the set temperature, the strip of tungsten metal should be hot enough to expand enough to open the circuit. When the temperature drops a little below the set temperature, the strip will contract thereby closing the circuit again and it will start heating again. This cycle will keep the temperature at the desired hotness.
Other than using to control heat, thermostats or thermal switches are also used to control cold, like the temperature of our fridge and our air conditioning unit. It works just the same as those thermostats used for heating only this time it will open the circuit when a certain coldness has been achieved and turns back on when the temperature rises beyond the desired temperature.