Simple bimetallic thermostats combine two strips of metal having different
coefficients of expansion joined together. When the strip is heated the
different expansion rates of the two metals causes the strip to bend and this
can be used to operate an electrical contact. Simple preset devices are usually
used for over-temperature protection e.g. domestic fan heaters and automatic
kettles, burnout for electric motors, etc. They can also be used as preset
thermostats for controlling temperature. This experiment illustrates the use of
a bimetallic strip sensing element to control temperature.