Physics
In a railway track, two rails are joined end to end with a gap in between them because

Accidents due to contraction in winter can be avoided
Air-gaps are necessary for bearing the weight of running train
Steel can be saved
Accidents due to expansion in summer can be avoided

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Physics
Rainbows are produced when sunlight :

Incident on raindrops hanging in the atmosphere is dispresed after suffering reflection.
Incident on rain drops hanging in the atmosphere is dispersed after suffering refraction
Incident on rain drops hanging in the atmosphere is dispersed after suffering refraction and internal reflection.
None of the given statements is correct.

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