# Application of Doppler’s effect

Application of Doppler’s effect – a) To determine the direction of motion of stars with respect to earth:
In astronomy, Doppler’s effect is used to determine whether a particular star or a galaxy is approaching the earth or moving away from the earth. Light from the star is observed with the help of a spectrometer. Several spectral lines are observed and these are compared with earth source. It has been generally found that the wave length of light received from the stars shifted slightly towards the red end of the spectrum. This is called RED SHIFT. It shows that the stars receding away from us and our universe are expanding.

b) To determine the speed of an approaching submarine:
Sound waves are transmitted in water from a ship towards the approaching submarine. The frequency of the reflected waves is measured by mean of a device, called SONAR (It stands for sound navigation and ranging). The velocity v of sound waves in water is calculated from the following relation:
v= √(B/ρ)
If n’ is the frequency of the reflected waves, then n’=[v/(v-vs)] × n.
Where n is the frequency of sound waves. The speed vs obtained from the above relation is halved to get the correct speed of approaching submarine. The speed v has to be halved because source is the sound-image of the oscillator on the submarine.
•You can calculate distance of submarines in sea and plane in sky.