Ever wondered the reason behind the change in frequency of sound of the siren of the ambulance or the plane? This is because of the Doppler effect. Doppler effect can be defined as the change in the frequency of the waves with respect to an observer. It is also known as Doppler shift.
In the year 1842, the Austrian physicist Christian Doppler discovered the effect as he noticed that when the ambulance crossed, there was a change in pitch as the ambulance passes. He observed that as the sound source approached him, the sound’s pitch was higher than the emitted frequency and as the sound source moved away from him, the sound’s pitch was receding.
Examples of Doppler Effect
Doppler radar is a common example of the Doppler effect. It is a radar beam that is fired at a moving target. The velocity of the target can be calculated by calculating the time taken by the beam to bounce off the target and return to the transmitter. This is used by the cops to identify people crossing the speed limits.
The second example where the Doppler effect is used is in astronomy. Here, it is used to determine the direction and rate at which planet or star or galaxy moves with respect to the earth. This is achieved by measuring either redshift or blueshift ie; the colour change in electromagnetic waves. Example of this is the red stars that are seen in the night sky, which means that the star is quite far from the earth.
The other example is in the field of medicine. Using the Doppler effect, the direction and velocity of blood can be determined. It is used in medical imaging and the term used is velocity measurement which measures the blood flow in arteries and veins and helps in diagnosing vascular problems like stenosis.
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