Physics XI Notes for Physics Notes

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Bimetallic Thermostat

Thermostat is a device which is used to maintain a desired temperature in a system like refrigerator, air-conditioner, iron and in a number of devices.

Thermostat works on the principle of thermal expansion of solid materials.

A bimetallic thermostat device consists of a strip of two different metals having different coefficients of linear expansion.
The bimetallic strip works as an electric contact breaker in an electric heating circuit. The circuit is broken when the desired temperature is reached.

bimetallic thermostat

Due to difference in the coefficients of linear expansion of two metals, The bimetallic strip bends in the form of a downward curve and the circuit is broken. The metallic strip is in contact with a screw ‘S‘. When it becomes hot, bends downward and contact at ‘P‘ is broken. Thus, the current stops flowing through the heating coil. When the temperature falls, the strip contracts and the contact at ‘P‘ is restored.

Bimetallic thermostats are widely used in numerous appliances such as refrigerator, air conditioner, Iron, ice plants etc.

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