Question

While laying the railway tracks on wooden plank, a small gap is left between the successive lengths of rail because
A. If no gap is left, the expansion of rails will cause them to bend sideways.
B. If no gap is left, the expansion will break the rails
C. If no gap is left, rails decrease in length
D. All

Answer 1

Hint
We would use the concept of thermal expansion. Some materials expand with increase in temperature and exhibit contraction on cooling. This can be used to explain the need of spacing to prevent accidents from happening.

Complete step by step answer
It is given that railway tracks have a small gap between successive rails. These gaps are known as expansion slots. We know that the railway tracks are made up of steel which is an iron and carbon alloy. When the tracks are subjected to seasonal temperature changes like for example in summer when the atmospheric temperature increases, it results in the tracks to expand thereby increasing track length. If there is no room left between the successive lengths of rail, then the rails will bend sideways as there is no space which allows increase of length. Similarly, on decrease in temperature in the winter season, the tracks contract and retain their original space. This small gap prevents the tracks from damaging in hot days.
Hence the correct option is (A). If no gap is left, the expansion of rails will cause them to bend sideways.

Additional Information
Thermal expansion is the process of increase of dimensions (length, height and thickness) of a material on heating. It is a three-dimensional enlargement. It can be represented as a ratio of change in length referred to as linear expansion or change in volume per unit temperature change which is volume expansion.

Note
The coefficient of linear expansion depends on the composition of the body. The coefficient of volume expansion is thrice of the linear expansion coefficient. This is in the case of solids.