Physics
A stone floor feels cold to the bare feet but a carpet on the same floor feels warm. This is because

The stone conveys the heat away from the feet more rapidly than the carpet
The human body maintains a constant temperature
The floor and carpet are at different temperatures
The carpet is a better conductor of heat than the stone

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Physics
Mirage is due to:

Equal heating of different parts of the atmosphere
Unequal heating of different parts of the atmosphere
Depletion of ozone layer in the atmosphere
Magnetic disturbances in the atmosphere

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Physics
What is refractive index ?

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