c is the wave velocity T is the time for the wave to move one wavelength distance. The Doppler effect finds applications in sirens used in emergency vehicles that have a varying pitch in. In contrast, waves emitted by a source travelling away from an observer get stretched out. Waves emitted by a source travelling towards an observer get compressed. This phenomenon was described by the Austrian physicist Christian Doppler in 1842. Doppler effect in physics is defined as the increase (or decrease) in the frequency of sound, light, or other waves as the source and observer move towards (or away from) each other. Suppose a source is moving almost but not quite at right angles to the line of sight, so that it has a large transverse velocity component, and a small velocity component towards the observer. Wave velocity c S/T In this equation, S defines the source’s wavelength. The Doppler effect is defined as the change in frequency or the wavelength of a wave with respect to an observer who is moving relative to the wave source. The light from the source is therefore seen by the observer to be redshifted, even though there is no radial velocity component.

Doppler effect formula