Question

Name two devices which use bimetallic strips.

Answer 1

Bimetallic strips have a band like structure made by joining different metals. Bimetallic strips are temperature sensitive, so they are used to convert a temperature change into mechanical displacement.

Complete answer:
The strip consists of two strips of different metals which expand at different rates when they are heated. Due to different expansions, the flat strip bends in one way if heated, and in the opposite direction if cooled below its initial temperature. The metal which has a higher coefficient of thermal expansion will be on the outer side of the curve when the strip is heated and on the inner side when cooled. Due to this effect, the bimetallic wires are used in a wide range of mechanical and electrical devices.

Thermometer and thermostat are examples of bimetallic tip devices.
(i) Thermometers: A thermometer uses a bimetallic strip, generally wrapped into a coil in its most used design. The coil changes the linear movement of the metal expansion into a circular movement due to the helicoidal shape it draws. One end of the coil is fixed to the housing of the device as a fixpoint and the other drives an indicating needle inside a circular indicator. A recording thermometer also uses a bimetallic strip.
(ii) Thermostat: The bimetallic strips are used in thermostats which operate over a wide range of temperatures for the regulation of heating and cooling.

Note:
Electrical devices: Bimetal strips are also used to protect circuits from an excess of current with the help of miniature circuit breakers. In this, the bimetallic strip is heated with a coil of wire, which bends and operates a linkage that unlatches a spring-operated contact. Due to this, the circuit gets interrupted and also protected from an excess of current.
Some other uses of the bimetallic strip are in Time-delay relays, Lamp flashers, and Mechanical PWM voltage regulators for automotive uses.