Why are gaps left between successive rails on a railway track ?

Why are gaps left in between rails, while laying a railway line? Explain.

A wire in the form of a tightly wound solenoid is connected to a DC source, and carries a current. If the coil is stretched so that there are gaps between successive elements of the spiral coil, then

How does the energy gap between successive energy levels in an atom vary from low to high n values?

The distance between two successive base pairs is

How do the energy gaps between successive electron energy levels in an atom very from low to high n values ?

The phase between the two successive M phase is called as

Small gaps are left between railway lines because :

The gap between any two rails each of length l laid on a railway trach equals x at 27^@C When the temperature rises to 40^@C the gap closes up. The coefficient of linear expansion of the material of the rail is alpha . The length of a rail at 27^@C will be

The period between two successive mitotic divisions is called as:

The gap between two neurons is called a