We were discussing a problem on the Resonance Tube Experiment in class when my teacher wrote down the following equations:
AN and N stand for the positions of the antinode and node, e stands for the end correction and l1, l2 and l3 are lengths of the tube in the three cases. What I am wondering is, why can't the end correction be applied inside the tube? Mathematically. why can't e be negative? Does this have anything to do with the reason for end correction?