after verifying angle i=r for reflection of sound, we lift one of the two pipes vertically to a small height, then :-
a)the reflected sound becomes louder
b)there is no effect on reflected sound
c) there is no reflection of sound
which of the following is correct and why? plz answer
All these variants are wrong. You will observe that the quality and the intensity of sound decreases when you lift one of the two pipes. This proves that the sound will be maximum when the incident beam, the reflected beam and the normal lie in the same plane.