Question

Some gap is left between two sectors of a bridge, why?

Answer 1

the gap is left between them as during summers the metal bridge expand on heating and fills the gaps if gaps are not made the bridge will break.
Hope this helps.

Answer 2

Thermal expansion is the reason we leave some gaps between sections of a bridge or two consecutive sections of railway tracks. With an increase in temperature (during daytime or during summer months), the bridge sections or the railway track sections will expand. With a drop in temperature (at night or during the winter), these sections will contract. If there was no gap between such sections, this regular expansion and contraction would cause stresses and enhanced wear and tear. In the case of bridges, this can also cause deflection of its sections.