Application of Doppler effect

What is application of Doppler effect?

Application of Doppler effect - a) To determine the direction of motion of stars with respect to earth:
In astronomy, Doppler 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 using Doppler effect:
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-v_s)] × n.
Where n is the frequency of sound waves. The speed v_s 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.

c) Radar:
Radar stands for radio detection and ranging. It measures not only the distance and location of an plane but also its velocity by determining the frequency shift. A radar transmitter stands out high frequency radio waves towards an plane. The echo of the reflected waves is detected by the receiver of the radar station. The difference of frequency of the transmitted waves and the reflected waves helps us to determine the speed of plane as discussed below:
We known that n’=[v/(v-v_s)] × n =n[(v-v_s)/v]^-1 or n’=n[1+(v_s/v)]= n+n(v_s/v)
Or n’-n=(v_s/v)× n or Δn=(v_s/v)×n
v_s=v(Δn/n)
Thus, by determining the frequency shift Δn, v_s can be calculated. This has to be halved to obtain the approach velocity of the plane.

D) Thief alarm using Dopppler effect:
This is device used for detecting a thief near the safe. In this device, an ultrasonic beam is sent, right from above the safe. Any movement of the thief near the safe will cause the change in the frequency of the reflected wave, sounding the alarm.