The Doppler Effect

When wave energy like sound or radio waves travel between two objects then the frequency seems to change if one or both of the objects are in motion.This phenomena in which received frequency is different from sent frequency due motion of receiver or the object (or both) is called Doppler effect. 

Let us consider a beetle that resides in the centre of a circular water puddle. The bug shakes its legs on a regular basis to create noises that move through the water. If the disturbances start at a single spot, they will spread outward in all directions from that point. Because all of the disturbances are going through the same medium, they will all travel at the same speed in all directions. A sequence of concentric circles would be generated by the bug’s shaking. At the same time, these rings would reach the margins of the water puddle. An observer is at point A (the puddle’s left edge) and  an observer is at point B (at the right edge of the puddle).If the bug creates disturbances at a rate of 2 per second, each observer will see them arriving at a rate of 2 per second.

Assume that our beetle is travelling to the right across the puddle of water, creating two disturbances every second. Because the bug is migrating to the right, each subsequent disturbance comes from a location closer to observer B and farther away from observer A. As a result, each subsequent disturbance travels a shorter distance before reaching observer B, taking less time to reach observer B. As a result, observer B notices that the frequency with which disturbances arrive is greater than the frequency with which disturbances are produced. Each successive disturbance, on the other hand, must travel a greater distance before reaching observer A. As a result, observer A notices a lower frequency of arrival than the frequency at which the disruptions occur. The total impact of the bug’s motion (the source of waves) is that the observer facing the insect sees a frequency more than 2 disturbances per second, while the observer facing away from the bug sees a frequency less than 2 disturbances per second. The Doppler effect is the name for this phenomenon.

Doppler Effect, and its working principle

When the source of waves moves in relation to an observer, the Doppler effect is detected. The Doppler effect is defined as the effect caused by a relative movement between source of waves and receiver that causes an increase or decrease in frequency for observers moving towards  the source and an apparent change in frequency for observers moving  away from the source. It’s vital to keep in mind that the effect isn’t caused by a change in the source’s frequency. The bug is still causing disturbances at a rate of 2 per second in the case above; it only looks to the observer who the bug is approaching that the disturbances are occurring at a frequency greater than 2 per second. Because the distance between observer B and the bug is reducing while the distance between observer A and the bug is expanding, the effect is only visible.

The Doppler effect can be seen in any sort of wave, including water, sound, and light. We are most familiar with the Doppler effect because of our encounters with sound waves. Perhaps you recall a day when you were driving along the highway and a police car or emergency vehicle approached you. The pitch of the siren sound (a measure of the frequency of the siren) was high as the car approached with its siren blaring, and then rapidly dropped as the car passed by. That was the Doppler effect: a sound wave created by a moving source appears to vary in frequency.

The Doppler Effect in Astronomy

Astronomers who use information about the shift in frequency of electromagnetic waves produced by moving stars in our galaxy and beyond to infer information about those stars and galaxies are understood by the Doppler effect. The theory that the universe is expanding is based on measurements of electromagnetic waves released by distant galaxies. Furthermore, the Doppler effect can be used to determine specific information about stars within galaxies. Galaxies are globular clusters of stars that spin around a central mass point. If a star rotates in its cluster in a direction away from the Earth, electromagnetic radiation emitted by such stars in a distant galaxy seems to be moved downward in frequency (a red shift). If the star is rotating in the direction of the Earth, however, there is an upward shift in frequency (a blue shift) of such measured radiation.

Conclusion 

The following findings are reached: If you (the observer) move in the opposite direction of the sound waves (source), the frequency of the sound waves (source) will appear to you to be higher. Similarly, if sound waves (the source) come towards you (the observer), their frequency appears to be higher than the beginning frequency.

As we know  the Doppler effect is dependent on moving things, it can be used to determine the motion or speed of an object. Interesting objects include the speed of a car on the highway, the velocity of blood running through an artery, the rotation of a galaxy, and even the expansion of the Universe.