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Explain working principle of bimetallic thermometer.

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image Working principle: Figure shows construction of bimetallic thermometer, it consists of bimetallic strip usually in the form of a cantilever beam, which is prepared from two thin strips of different metals having different coefficient of thermal expansion. The bonding of two strips is done by welding such that they can not move relative to each other. Brass is used as a high expansion metal and Invar (alloy of iron-nickel) is used as low expansion metal. As the temperature applied to the strip increases, there is deflection of the free end of the strip as shown in figure. The length of metal will change according to the individual expansion rate. As one end of bimetallic strip As one end of bimetallic strip is fixed, the strip will bend at free end towards the side that of low coefficient of thermal expansion metal. The deflection of the free end is directly proportional to the square of the length of the metal strip, as well as to the total change in temperature, and is inversely proportional to the thickness of the metal. Pointer is attached to the free end to indicate the temperature

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