Physics
RADAR is used for:

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

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Physics
Stationary wave is formed by

Two waves of the same speed superposing
A transverse wave superposing a longitudinal wave
Two waves of same frequency travelling in the opposite direction
Two waves of same frequency travelling in the same direction

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