Frequency of sound, light and Doppler effect

The frequency of sound has characteristics that are characteristic of a number of other phenomena propagating through the wave. This is true, for example, for light or X-ray radiation. The frequency of sound is a certain physical quantity, which is characterized by a constant number of repetitions. It is determined by the ratio of the number of waves to the time interval for which they occur. For example, the frequency of the sound determines its height, which we hear. Or do not hear if the oscillations are beyond the limits of our hearing capabilities - infra- or ultrasound. If we are talking about light radiation, then depending on its frequency and wavelength, we see different colors of the spectrum: from red to blue.

The frequency of sound and the Doppler effect

An interesting phenomenon related to the considered quantity is called the Doppler effect (after the name of the pioneer scientist). It can be observed with the example of light waves, but the speed of light propagation is very high (about 300 thousand kilometers per second), and this makes it very difficult to observe it in everyday conditions. And the speed of propagation of sound waves is much lower. So, what is the Doppler effect? Imagine if you are on the roadside side of the highway, and a car with a working siren approaching you from far away. When he is still far away, the roar of the siren will seem deaf to you. This means that the frequency of sound is low. But as it approaches, it will grow more and more. You will be able to hear a higher and higher pitch tone, which will peak when the car passes you. When the object passes you and again disappears, the wavelength of the sound will again decrease (literally, smooth, if it is depicted on the graph). This is due to the fact that the sound of the siren first "catches up" with the machine in some way, which shortens the distance between the depressions (crests) of the wave and makes the tone higher, and then, on the contrary, "runs away," so that the wave is "smoothed out". Actually, this is called the Doppler effect.

Effect Value

However, we should not assume that the Doppler effect is some kind of dry fact from the world of electrodynamics. It is this knowledge that is widely used in modern sound radars, which are based on the measurement of wave frequencies. And in the same way, the traffic police determine the speed of vehicles, and other relevant services - the speed of aircraft, the flow of rivers, etc. By this principle, work and security alarms that react to movement in the room.

The opening of Edwin Hubble

But, probably, the most significant discovery related to this effect is the Hubble law. As early as 1929, the US astronomer Edwin Hubble sent his telescope to the starry sky. Watching distant galaxies, he discovered an interesting thing. Many of these galaxies were shrouded in a halo of red haze. As the sound of the receding object is heard to us higher, so the color of the receding body seems reddish to the human eye. It literally meant that the galaxies are flying away from us. It is interesting that the further the galaxy is located, the faster it is removed. This observation greatly contributed to the idea of the expanding universe and the Big Bang, which was the most popular among modern astrophysicists, as its beginning.