Question

What is effect of wind on apparent frequency of sound heard by the observer

Answer 1

Frequency of sound waves will remain constant due to wind.

Wind has essentially the same effect as an increase or decrease in sound velocity. If the crests are moving with the wind (in the same direction as the wind), then sound velocity is effectively increased.

But at the same time wind also increases the wavelength of the sound waves.

we know that,

wavelength x frequency = speed

=> frequency = speed/wavelength

Hence when neither the source nor the observer is moving then the change in speed and wavelength due to wind will be same. Hence frequency will remain constant due to wind.

The reverse is also true due to wind in the opposite direction when speed and wavelength will decrease but frequency will remain constant.