Question

How is bimetallic strip used in fire alarm

Answer 1

bimetallic strip=A bimetallic strip is used to convert a temperature change into mechanical displacement. The strip consists of two strips of different metals which expand at different rates as they are heated, usually steel and copper, or in some cases steel and brass

fire alarm:-
When a bimetallic strip, commonly made of iron and brass  is heated, both metals expand differently, causing the bimetallic strip to bend.
Thus, when a fire occurs, the heat of the fire causes the brass and iron strips to expand, ultimately resulting in the bending of the bimetallic strip, which on bending touches the screw adjacent to it, thus completing the circuit. Once the circuit is complete, the bell begins to ring.

Answer 2

Explanation:

The alarm contains two metal strips, one of the iron and other of brass, firmly bolted together. Brass expands more on heating, therefore the bimetallic strip bend on the side of iron upon heating and the circuit is completed. Hence, the fire alarm bell rings.