Question

A bimetallic strip made up of iron and brass; when heated in a flame:

A. The iron expands more than brass
B. The brass expands more than iron
C. Both iron and brass expand equal
D. None of these

Answer 1

A bimetallic strip is a strip used as temperature sensitive contacts when exposed to temperature expands at different rates due to its different composition which is iron and brass and hence when such different expansion occurs, it causes the strip to bend due to different thermal coefficients of expansion of the metals.
Thermal coefficients determine how the size of an object changes with a change in temperature.

Complete step by step answer:
When the bimetallic strip is heated, brass expands more than steel due to higher thermal coefficient than steel. If we compare the thermal coefficient of both materials, it is about 1.5 times higher in case of brass than steel.
higher thermal expansion coefficient means that substance will expand more as compared to any other substance per degree rise in temperature.
And hence due to this phenomenon brass side shows higher expansion especially linear expansion than iron and hence forcing the whole bimetallic strip to bend.
So, the correct answer for this question is brass expands more than iron which is option B.

Note:
Materials having low thermal expansion coefficients make them stabler over wide temperature ranges.
Materials have three types of thermal expansion coefficients.
1. linear expansion coefficient
2. Area expansion coefficient
3. Volume expansion coefficient
When material is heated, its molecules get excited and are energized from the thermal energy and hence the average distance between them increases making the overall material expand.