Explain why gaps are left between railway lines​

to prevent the derailing of the train due to thermal expansion.

Iron are good conductors of heat and electricity. Being a good conductor it expands as well as contracts with the change of temperature.When heat is applied,they expands because molecules inside the element gets excited and number of molecules inside it increases in tremendous amount,so it leads to expansion of iron. So when the temperature is lowered it comes in its normal state.

The term for this is called as thermal expansion or contraction.The gap in the joint between 2 rails is to prevent from the expansion of the iron. It is necessary ,if not there will be change in structure,it may buckle and chance of derailed is increased.

Explanation:

The gap in the joint between to rails is to compensate for the expansion of the material of rail during summer.

The metals expand or contract with the changes in temperature. The expansion or contraction depends on the coefficient of thermal expansion of the material. Based on this property of the metal, the gap in the joint of two rails is provided.

if the thermos has a vacuum innner, then heat through conv currents and conduction are reduced = vacuum flask