'The person standing behind the open door inside the room can hear the voice of this person standing on the other side of the door but they cannot see each other". Give experiment based on the diffraction for this statement.

Explanation

Take the average wavelength of visual light `lamda=6xx10^(-7)` m and he width of our window or door is d=1 m, then `(lamda)/(d)=6xx10^(-7)`. Because of its small value, the waves of light does not bend. That is diffraction of light is negligible.
While in normal conversation the sound frequency is between 100 Hz to 400 Hz. For the sake of simplicity, suppose the frequency of sound is 330 Hz and velocity of sound in air is 330 m/s. So wavelength `lamda=(v)/(v)=(330)/(330)=1m` and width of window or door d = 1 m then `(lamda)/(d)=1` which is the maximum value of diffraction. Hence, sound waves have a diffraction range of `0^(@)` to `90^(@)`. So sound can be heard in normal conversation but diffraction of light is negligible so we cannot see the person.