(iv) If the source is situated at the center of the circle along which the listener is moving. . . Applications of Doppler effect (a) To measure the speed of an automobile An electromagnetic wave is emitted by a source attached to a police car.
The wave is reflected by a moving vehicle, which acts as a moving source. There is a shift in the frequency of the reflected wave. From the frequency shift, the speed of the car can be determined. This helps to track the over speeding vehicles.
(b) Tracking a satellite The frequency of radio waves emitted by a satellite decreases as the satellite passes away from the Earth. By measuring the change in the frequency of the radio waves, the location of the satellites is studied. (c) RADAR (RAdio Detection And Ranging) In RADAR, radio waves are sent, and the reflected waves are detected by the receiver of the RADAR station. From the frequency change, the speed and location of the aeroplanes and aircrafts are tracked.
(d) SONAR In SONAR, by measuring the change in the frequency between the sent signal and received signal, the speed of marine animals and submarines can be determined. Points to Remember Wave velocity is the velocity with which the wave travels through the medium. Velocity of a sound wave is maximum in solids because they are more elastic in nature than liquids and gases. Since gases are least elastic in nature.
Infrasonic waves are sound wave with a frequency below Hz. A human ear cannot hear these waves. Ultrasonic waves are sound waves with frequency greater than kHz, A human ear cannot detect these waves. Reflection of sound waves obey the laws of reflection.
when a compression hits the boundary of a rarer medium, it is reflected as a rarefaction. An echo is the sound reproduced due to the reflection of the original sound wave. The minimum distance between the source and the reflecting surface should be . m to hear an echo clearly.
“The apparent frequency” is the frequency of the sound as heard by the listener.