Answer to Question #161980 in Optics for Fletcg

Question

The radar systems used by police to detect speeders are sensitive to the Doppler shift of a pulse of microwaves. Explain how sensitivity can be used to measure the speed of a car.

Answer 1

Doppler effect:

It is the phenomena in which there is an apparent change in frequency due to relative motion between the source and observer.

Doppler shift:

It is the amount of the change in the observed frequency of a wave due to Doppler effect.

The speed of car can be determined in a simple manner. First a beam of radio waves of known frequency is sent towards a speeding car, which reflects the beam back to a detector of the police car. We can observe that the amount the returning frequency has been shifted depends on the velocity of the oncoming car.