Name any three application of Doppler's effect ?

Explanation

Doppler shift in frequency or wavelength of electromagnetic radiations is used
(1) by astronomers to determine the radial velocities along the line of sight of stars and galaxies. From the Doppler redshifts of galaxies, we infer that the universe is expanding, which is one of the most important pieces of evidece in support of the Big Bang model. Distant galaxies are moving away from us extremely fast, faster than nearer galaxies.
(2) by astronomers to determine the rotational speed of the Sun from the Doppler shift in the Fraunhofer lines in the solar spectrum from the two diametrical ends of the solar disc. Some of the absorption lines in the solar spectrum are due to absorption by atomic oxygen in the Earth's outer atmosphere. Hence, coinciding the atmospheric oxygen lines in the two spectra, the Doppler shifts of lines from iron are measured. As the Sun rotates about its axis, one end approaches us, while the other end recedes away. Measurements show that the rotational speed of the Sun at the equator is nearly 2 km/s.