Consider a source produces sound of frequency f. If v is the speed of sound in air, then the wavelength of the sound wave
λ = v/f
Now suppose the observer O moves towards stationary source with a speed of vO. The speed of sound relative to observer
v' = v + vO
As the source is stationary, so wavelength of the sound wave remain same. Because of the increased relative speed of the sound, the frequency appears to increase . Thus apparent frequency
![](https://www.sarthaks.com/?qa=blob&qa_blobid=805812106767198338)
If the observer moves away from the stationary source, then
![](https://www.sarthaks.com/?qa=blob&qa_blobid=1729609728284469663)
General Doppler effect equation:
The apparent frequency can be written as ;
![](https://www.sarthaks.com/?qa=blob&qa_blobid=12309832008247009548)