Physics
Railway tracks are banked on curves so that

The train may not fall down inwards
Necessary centrifugal 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 centripetal force may be obtained from the horizontal component of the weight of the train

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Physics
Purpose of an optical filter is to

Reflect lights of different colours
Refract light of different colours
Transmit or absorb light of different colours
Dispense light into component colours

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