Physics
In total internal reflection, the light travel from

Denser to rarer medium and it occurs with no loss of intensity
Rarer to denser medium and it occurs with no loss of intensity
Denser to rarer medium and it occurs with loss of intensity
Rarer to denser medium and it occurs with loss of intensity

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

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