Physics
Railway tracks are banked on curves so that

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

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Physics
'Mirage' is an example of

Total internal reflection of light only
Refraction and total internal reflection of light
Refraction of light only
Dispersion of light only

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