Physics
The phenomenon of light associated with the appearance of blue colour of the sky is

Interference
Reflection
Refraction
Scattering

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Physics
Why two thin shirts can keep us warmer than a single thick shirt in winter ?

Two thin shirts become thicker so prevent transmission of heat
No radiation of heat takes place
Air layer between two shirts behaves like insulating media
Air layer between two shirts works as good conductor

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Physics
Railway tracks are banked on curves

to avoid frictional force between the tracks and wheels
necessary centripetal force may be obtained from the horizontal component of the weight of the train
the train may not fly off in the opposite direction
necessary centrifugal force may be obtained from the horizontal component weight of the train

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