Answer :
Answer and Explanation:
The process of change in the frequency due to change in distance between the source and observer is known as Doppler effect.
There are two parts in this effect either change in frequency due to change in relative motion of source and observer in same direction or change in frequency due relative motion of source and observer in opposite direction.
Example of Doppler effect
The best example of Doppler effect is that the frequency of sound increases when source comes closer to observer.