How do police find out if you are speeding?« Back to Questions List

Doppler Effect was found by Austrian physicist Christian Doppler. It simply describes how light, sound or even water waves behave with reference to a stationary object. A simple way to understand Doppler Effect is to imagine a moving train and the stationary observer in the station. When the train approaches the station (observer), the pitch of the train whistle heard is high and when the train moves away from the station, the pitch of the sound heard becomes low.

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The Doppler Effect is used in measuring changes in the frequency of light or sound waves when the source moves either towards or away from the listener.  Doppler Effect is used in radar (radio detection and ranging) systems. Radar guns are devices that have a transmitter and a receiver.

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Police use radar guns, using which they shoot at the moving vehicle. The gun shoots radio waves at a particular frequency and measures the frequency of the waves reflected from the moving vehicle. When the vehicle travels faster towards the direction of the gun, frequency returned to the gun is high. The difference in frequency is calculated from which the device calculates the speed of the vehicle and displays the same.What is the role of Doppler radar in weather forecasting?


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