# The Doppler Effect

Doppler effect is one of the most remarkable discoveries in the study of the properties of wave phenomena.Its versatile character determines what is today on the basis of this effect are thousands and thousands of the most diverse devices in various spheres of human activity.The phenomenon, which is then received the name in honor of its discoverer, was discovered by Christian Doppler Austrian physicist back in the mid-nineteenth century.Doppler measurements of the properties carried out waves that came to the receiver of the mobile and stationary sources.

If we consider the Doppler effect in its simplest form, it should be noted that the physical phenomenon describes the change in frequency of the signal with respect to the amount of movement of the source of the signal from the receiver that receives it.For example, a wave that comes from a source and which has a certain fixed frequency is received by a receiver on another frequency, if it passes over the source and receiver are replaced by their position relative to each other, that is shifted.When this increase or decrease the frequency component depends on the direction in which the source moves relative to the receiver.Taking into account the Doppler effect, you can definitely say that if the receiver is removed from the source - frequency wave decreases.If the receiver is approaching the wave radiation source, then the measure of frequency of the wave increases.Accordingly, these patterns is concluded that if the source and receiver wave during its passage not changed its position, and the wave frequency remains unchanged.

important and another clause which characterizes the Doppler effect.This property is to a certain extent is in contradiction with the laws of relativity.The fact that the value of the frequency change is determined not only by moving or not the radiation source and the receiver, and by the fact that it moves.Measurements have shown that the frequency shift is determined by what kind of object is mobile, the more noticeable the smaller the difference in the speeds of displacement of the receiver and the source of the speed 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 can not be detected because there are not important to the relative movement of the receiver and source, and the nature of the movement of the waves in an elastic medium in which it moves.Such properties

Doppler effect manifests itself in relation to the origin of the acoustic waves and electromagnetic waves, except that in the case of electromagnetic waves with a frequency shift phenomenon does not depend on the source or the receiver moves.

How does this rather abstract effect, see, however, is simple enough.For example, the Doppler effect in acoustics can be seen, to be exact - to hear, at a time when standing in a traffic jam, you hear a siren sound a passing emergency vehicles.Probably all noticed that if such a vehicle is approaching - the sound of the siren sounds one way high, and when a vehicle ahead of you - the sound of sirens below.It just confirms that changes the frequency of the acoustic signal.

great importance frequency Doppler radar plays, with respect to electromagnetic waves.On the basis of this effect work all radars and other devices detect moving objects in various fields of human activity.

Its properties are used in medical technology for determining blood flow, widely known as such a procedure as Doppler echocardiography.On the basis of the Doppler effect built appliances provide navigation for underwater vessels using it meteorologists measure wind force and speed of the cloud masses.

even astronomy in their measurements using the Doppler effect.Thus, the largest displacement of the spectra of different astronomical objects is determined by the speed of their movement in space, in particular, is based on this effect has been hypothesized expansion of the universe.