Doppler Effect

The Doppler effect is one of the remarkable discoveries in the field of studying the properties of wave phenomena. Its universal character is determined by the fact that today on the basis of this effect thousands of thousands of the most diverse instruments work in various spheres of human activity. The phenomenon, which was later named after its discoverer, was discovered by the Austrian physicist Christian Doppler in the middle of the nineteenth century. Doppler measured the properties of the waves that came to the receiver from a moving and stationary source.

If we consider the Doppler effect in its simplest form, then it should be noted that this physical phenomenon describes the change in signal frequency relative to the amount of movement of the source of the signal itself from the receiver that receives it. For example, a wave that comes from some source, and which has some fixed frequency, will be received by the receiver already on another frequency, if during its passage the source and receiver changed their location relative to each other, that is, they moved. At the same time, the frequency index will increase or decrease, depending on which direction the source moves relative to the receiver. Considering the Doppler effect, it can be unequivocally asserted that if the receiver is removed from the source - the value of the frequency of the wave decreases. If the receiver approaches the source of wave radiation, then the indicator of the frequency of the wave increases. Accordingly, it follows from these regularities that if the source and the receiver of the wave did not change their location during its passage, then the value of the wave frequency will remain the same.

Important is another clause that characterizes the effect of Doppler. This property to a certain extent comes into conflict with the laws of the theory of relativity. The point is that the value of the frequency change is determined not only by whether the receiver and the source of radiation move or not, but also by what exactly moves. Measurements have shown that the frequency shift, determined by which object is mobile, is the more noticeable, the smaller the discrepancy in the velocities of the receiver and source displacement from the velocity of the wave. In fact, in cases where there is a manifestation of the Doppler effect, there is no contradiction with the theory of relativity, because here it is not the relative motion of the receiver and source that is important, but the nature of the wave moving in the elastic medium in which it moves.

Such properties of the Doppler effect also show with respect to waves of acoustic origin, and to electromagnetic waves, except that in the case of electromagnetic waves, the frequency shift phenomena do not depend on whether the source or receiver moves.

As this rather abstract effect manifests itself, it is nevertheless quite easy to see. For example, the Doppler effect in acoustics can be seen, more precisely - heard, at a time when, while standing in the traffic jam, you hear the signal of a siren passing by a special vehicle. Surely everyone noted the fact that if such a car is approaching - the sound of the siren sounds one way, high, and when such a car passes you - the sound of the siren is lower. This just confirms the presence of a change in the value of the frequency of the acoustic signal.

Doppler frequency plays a huge role in radar, with reference to electromagnetic waves. Based on this effect, all radar stations and other devices for detecting moving objects in the most diverse fields of human activity operate.

Its properties are used in medical technology to determine blood flow, a procedure known as Doppler echocardiography is also widely known. Based on the Doppler effect, navigational support devices for submarine vessels have been constructed, with its use meteorologists measure the strength of the wind and the velocity of cloud mass movement.

Even astronomy in its dimensions uses the Doppler effect. Thus, in terms of the displacement of the spectra of various astronomical objects, their speed of movement in space is determined, in particular, it is on the basis of this effect that the hypothesis about the expansion of the universe was put forward.