Physics
Railway tracks are banked on curves so that

Necessary centripetal force may be obtained from the horizontal component of the weight of the train
No frictional force may be produced between the tracks and the wheels of the train
Necessary centrifugal force may be obtained from the horizontal component of the weight of the train
The train may not fall down inwards

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Physics
In total internal reflection, the light travel from

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

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