The image produced by an echo-cardiogram shows the edges of heart structures, but it cannot measure the speed of blood flowing through the heart. In this case, the stationary transmitter is located in a weather station and the moving object being studied is a storm system.ģ) Doppler echo-cardiogram: A traditional echo-cardiogram uses sound waves to produce images of the heart. By measuring the change in frequency of the rebounded wave, the speed of the vehicle can be measured.Ģ) Meteorologists use a similar principle to read weather events. The faster the car's speed, the higher the frequency of the returning wave. Because the car is moving toward the gun, the frequency of the returning waves will be higher than the frequency of the waves initially transmitted by the gun. The radar gun measures the frequency of the returning waves. The radio waves strike the vehicle and bounce back toward the radar gun. The gun sends out a burst of radio waves at a particular frequency. The officer aims his radar gun at an approaching vehicle. Following are a few applications of it.ġ) The handheld radar gun used by traffic police to check for speeding vehicles relies on the Doppler effect. The Doppler effect finds applications in a variety of fields. A positive value is used for motion of the observer or the source toward the other, and a negative sign for motion of one away from the other.

The observer moves with a speed v o v s depend on the direction of the velocity. For simplicity, we assume that the air is also stationary and that the observer moves directly toward the source. In this case, an observer O is moving and a sound source S is stationary. Let us now examine a situation with sound waves. When the boat is turned around and move to the left, the relative speed is lower, as is the observed frequency of the water waves. When the boat is moving towards the right, this relative speed is higher than that of the wave speed, which leads to the observation of an increased frequency. These effects occur because the relative speed between the boat and the waves depends on the direction of travel and on the speed of the boat. Thus, a lower frequency than when you were at rest will be observed.īoat moves in the direction of water waver and water waves hit the boat from behind Because the boat is now moving away from the next crest, more than 3.0 s will elapse on the watch by the time that crest catches the boat. The watch is set to t = 0 as a crest hits the back of the boat. If the boat is turned around and move in the same direction as the waves, the opposite effect is observed. Because f = 1/T, a higher wave frequency is observed than when the boat was at rest. In other words, this period observed is shorter than the 3.0 s period observed when the boat was stationary. Now, however, because the boat is moving towards the next wave crest as it moves toward the boat, it hits the boat in less than 3.0 s after the first hit. Again, the watch is set to t = 0 as a crest hits the front of the boat. Now suppose the boat is headed directly into the incoming waves. If a watch is set to t = 0 just as one crest hits, the watch will read 3.0 sec when the next crest hits and 6.0 sec when the third crest hits, and so on.Ī person in a boat with water waves moving towards himįrom these observations, it can be concluded that the wave frequency is f = 1/T = 1/(3.0 s) = 0.33 Hz. The following figure shows this situation, with the water waves moving toward the left. This means that every 3.0 second a crest hits the boat. To see what causes this apparent frequency change, imagine a boat that is lying at anchor in a gentle sea where the waves have a time period of T = 3.0 sec.

Doppler effect formula