When there is a relative motion between a source of sound and an observer, there is apparent change in frequency of a sound emittedby a source and as heard by the observer is called deppler effect.
The doppler effedct causes the received frequency of a source ( how i9t is perveived whe3n it gets to its destination) to differe form the sent frequency if there is motion i.e., increasing or decreasing the distance between the source and the receiver. This effect is readily observable by the variation in the pitch of sound between a moving source and a stationary observer. Four applicationls of doppler effect include :
(a) The handhled redar guns used by police to check for speeding vehicles rely obn teh Dopler effect.
(b) Meterologists use a similar principle to read weather events. It this case, the stationary transmitter is located in a weather station and the moving object beign studied is a strom system.
( c) It is used to determine the speed of rotation of the sun.
The dopple effect is used sonography. In this the ultrasonic waves reflected from body tisues can give informationo about the rate of flow of various fluids including blood.
