Physics
What is refractive index ?

It is defined as the ratio of speed of light in the medium to the speed of light in vacuum.
None of above
It is defined as the product of speed of light in medium and in vacuum.
It is defined as the ratio of speed of light in vacuum to the speed of light in the medium.

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Physics
A cyclist leans inwards when he is negotiating a curve so that

No frictional force may be produced between the wheels and the axle
He may increase his speed
Necessary centripetal force may be available from the horizontal component of the normal reaction due to the track to maintain the curved motion.
His weight may be reduced

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