what is the doppler effect ?

Answer 1

Suppose we are standing in a railway platform, the pitch [frequency of sound] of the whistle of the engine increases when the engine is approaching us and decreases when the engine moves away from us.

The apparent change in the frequency due to relative motion between the source and the observer is called Doppler Effect.
This effect is observed in the case of light waves too.

Doppler Effect in sound is asymmetric. The apparent frequency, when the source moves toward the observer is different from that when the observer moves toward the source.

The loudness of the whistle will increase when the engine comes toward us and will decrease when it moves away from us. Doppler Effect is about frequency and not about the loudness of sound or intensity of light

Answer 2

The Doppler effect, named after Christian Doppler, is the change in frequency and wavelength of a wave as perceived by an observer moving relative to the source of the waves. For waves that propagate in a wave medium, such as sound waves, the velocity of the observer and of the source are relative to the medium in which the waves are transmitted. The total Doppler effect may therefore result from motion of the source or motion of the observer or motion of the medium. Each of these effects is analyzed separately. For waves which do not require a medium, such as light or gravity in special relativity, only the relative difference in velocity between the observer and the source needs to be considered.

Answer 3

The Doppler effect is indeed a change in frequency resulting from a relative velocity between the source and the observer.

Here's why it works:

An approaching train emits a series of sinusoidal sound waves as it departs. One wave is created at one location, the next wave is created at a further distant location, the next wave at an even further distant location, and so on. These waves all travel at the same speed to reach your ears on the platform. Since the waves were emitted from further and further away, the distance between each wave peak initiation is added to the normal wavelength. Therefore, you perceive the sound as having a longer wavelength, which means a lower pitch.

The opposite happens when the train is approaching, and the waves are shortened by the difference between the locations where they were emitted.

This works for light as well as sound, because light travels at a constant speed - note that the Doppler effect does not change the speed of propagation.

Answer 4

The doppler effect is the shift of wavelength (and therefore frequency) in light or sound when there is relative motion between the observer and the source. If the observer and source are moving toward each other, the wavelength of the waves will appear shorter compared to the waves measured in a reference frame moving with the source. This is often called the blue shift, since blue is at the short end of the visible spectrum.

If the observer and source are moving away from each other, the waves will be measured to have a longer wavelength; this is called a red shift.

Answer 5

A Doppler shift experiment involves a source that emits successive short signals at constant time intervals (period of emission) which are received by an observer in constant relative motion with the source at constant time intervals (period of reception. The Doppler shift formula relates the two periods mentioned above.
The successive signals could be bullets fired by a machine gun which hit a target (a look at “Teaching
the Doppler shift using a machine gun analogy,” Phys.
Teach. 39, 468–469 (Nov. 2001)" could be of help)
The successivelly emitted signals could also be the wave crests of an acoustic wave or of an electromagnetic wave or short light signals emitted by a laser gun.
The emission period and the reception period are related by the Doppler factor which depends on the relative speed between source and receiver, on the speed at which the successive signals propagate from the source to the receiver. It is one of the most derived formula and we know formulas derived in the limits of classical physics but also in the limits of special relativity theory. It is used in radar detection, relative speed measurement and many other technical application. A look at google will bring a huge quantity of information/

Answer 6

The Doppler effect is something that seems to grow louder as it approaches you and has decreasing volume as it goes away from you such as a train coming down the track towards you and vanishing in the distance after it has passed.