Physics
RADAR is used for:

receiving a signals in a radio receiver.
detecting and locating the position of objects such as Aeroplanes.
locating geostationary satellites.
locating submerged submarines.

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Physics
What is refractive index ?

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

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