Question

The gaps are kept in the railway track so that
A) The friction is produced and the speed of the train may not increase beyond a limit
B) The friction between wheels and track
C) The replacement of the track is easier when there is fault in the track
D) The expansion of the track will take place due to friction as well as in summer

Answer 1

When the temperature of the solid material is increased or decreased it expands in response to an increase in temperature and shrinks in response to a decrease in temperature. When the temperature of the solid material is increased then the length of the solid material also increases. The increase in length of the solid material is called thermal expansion.

Step-by-step solution:
If original length of the solid material is${{l}_{o}}$
The coefficient of thermal expansion of the solid material is$\alpha$
Let the change in temperature of the solid material is $\Delta T$
Then the change in the length of the solid material can be calculated as,
$\Delta l={{l}_{o}}\alpha \left( \Delta T \right)$
Let two tracks be in contact with each other. With rise in temperature of the surrounding, the length of the track increases. The increase in length of the track can cause the track to bulge out of the horizontal level. This can cause train accidents.
Therefore the gap is left between the rails to provide a space for the iron metal to expand and contract during the summer and winter season due to the change in the temperatures. If the gap is not left in between then the rails will bend more and cause derailing of the trains.

When there is relative motion between the surface of the track and the wheel of the train, due to frictional force there is shear force applied; the railway track shows expansion in length. To avoid this gap is left between the rails.

Hence, option D is the correct option.

Note:
-The thermal expansion of matter depends on the type of material used in the matter.
-The temperature difference is calculated by subtracting the initial temperature from the final temperature.