RADAR operates on which principal?

The correct choice relates to the Doppler Principle, which is fundamental for how RADAR operates. The Doppler Principle is based on the change in frequency of a wave in relation to an observer moving relative to the source of the wave. In the context of RADAR, it is used to measure the velocity of a target by analyzing the frequency shift of the returned signal after it has bounced off the target.

When a RADAR system emits a wave and it encounters a moving object, the frequency of the reflected wave changes depending on whether the object is moving towards or away from the RADAR system. This frequency shift allows the RADAR to not only detect the presence of the object but also to measure its speed and direction of movement. This capability is essential in various applications, from weather monitoring to air traffic control and law enforcement for speed detection.

The other principles do not directly apply to how RADAR functions. The absorption principle refers to the loss of signal strength as it passes through a medium, which is not the primary method of operation for RADAR. The refractive principle relates to the bending of waves as they pass through different mediums, which is less relevant for the RADAR's functionality. The reflective principle is somewhat related since RADAR does rely on