A bimetallic strip is a device used in thermostats and mechanical thermometers. It consists
of bonded strips of two metals with dissimilar
coefficients of thermal expansion. When
heated, the bimetallic strip bends because one metal expands more than the
other. This reversible distortion is used to move a dial pointer or to open
or close a switch in an electric circuit.
|A bimetallic strip thermometer uses a helical metal
strip that unwinds when heated and rotates a pointer over a calibrated
scale. When warmed, one metal (usually copper) expands more than the
other (usually Invar), so causing the bimetallic strip to unwind.
Invar is an alloy of iron and nickel, which has a low coefficient
of thermal expansion.