Question

Bimetallic strips are used in fire alarms.

(A) True

(B) False

Answer 1

Bimetallic strip has different types of strips (having different coefficients of thermal expansion) and with an increase in temperature strips bend which can be used to trigger a certain type of alarm.

Complete answer:

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. The different expansions force the flat strip to bend one way if heated, and in the opposite direction if cooled below its initial temperature. The metal with a higher coefficient of thermal expansion is on the outer side of the curve when the strip is heated and on the inner side when cooled.

Every metal has a different temperature coefficient. The temperature coefficient shows the relation between the change in the physical dimension of metal and the temperature that causes it. The expansion or contraction of metal depends on the temperature coefficient, i.e., at the same temperature the metals have different changes in the physical dimension.

Fire alarms are mostly triggered when certain smoke is detected and the alarm is triggered without any increase in temperature or increase in heat so a bimetallic strip cannot be used in fire alarms as most of the temperature increase occurs after the fire has burned everything and then there will be no use of fire alarms if everything is burned down.

Hence, the correct answer is (B) False.

Note: It sounds intuitive that a bimetallic strip is used in fire alarms because both in some way involves heat but it’s not true because fire alarms are installed to prevent fire and if we use a bimetallic strip then the alarm will buzz once everything is burned down which will be of no use to us.