 We will heat a bimetal strip. A bimetal strip consists of two strips of different metals bonded to each other. As you heat the bimetal strip, the two different metals expand at different rates. This causes the metal strip to curl. Many thermostats employ a bimetal strip to operate. If we take the cover off the thermostat, we'll see a small metal coil, which is actually a bimetal strip. That bimetal strip is attached to a vial containing mercury and two electrodes. The mercury provides electrical contact between the two electrodes. As the temperature in the room changes, the coil of the bimetal strip either coils or uncoils. As it does so, it tilts the vial and the mercury makes contact or breaks contact with the electrodes. This turns the furnace of water off.