Which one of the following indicates a drop in temperature? a. the alcohol in a thermometer expands. b. the brass on a bent bimetallic strip is on the outside curve. c. the column of liquid in a thermometer moves up three degrees. d. a bimetallic strip bends so that the steel is on the outside curve.

A bimetallic strip bends so that the steel is on the outside curve.

Explanation:

A bimetallic strip is a combination of two different metals. The linear  coefficient of expansion of various metals are different, depending on their characteristics. For example, when a bimetallic strip of brass and steel are taken, thermal expansion coefficient of brass is more than that of steel.

That implies brass expands more than steel, for a given amount of heat supplied. So brass will curve outward since it becomes longer compared to steel. Steel will curve inwards.

Similarly, for cooling process where a drop in the temperature occurs, brass contracts more compared to steel and so Steel will be on outside curve.