Hi guys I am a A level student. Lately, i have done a practical investigation on pressure difference of the sounds in the air (Inside a both opened end tube). There is some question that i would like to know and I am wondering If anyone could help me please? The experiment is carried out by varying the distance of the microphone to the speaker inside the tube. Before the experiment was carried out, I have expected to see a sine graph. At both the open end, the pressure variation is at its minimum; therefore the EMF generated by microphone will be the smallest. (Note: the reasons saying it is a sine graph is that a microphone is detecing the pressure.... not the displacement of air molecules) Well, the experiment did verify my hypothesis; nevertheless, a bizarre data occurred to me that the EMF dropped from 100mv to 49mv upon reaching the end. (the 100mv is obtained at a distance 1 or 2 cm away from the open end). Before that, the EMF varied gradually, but it decreases rapidly as the microphone approaching the open end. The only explanation I could think of is that the air molecule moves freely at the opened end ( As it is just beside the “outside of the tube”). However, since there will be some reflection as a result of the collision of the air molecules at the opened end, the pressure variation should not be very low, at least not decreased rapidly… the picture attached shows the setup of my instruments. The sequence of the EMF from one open end A to another B is 49, 160, 190, 210, 250, 280,320, 360, 400, 440, 487, 520, 487, 440,400, 360,320, 280, 250, 210, 190, 160, 49 Notice that the EMF changes rapidly upon reaching A and B.