Question

550 Hz sound is emitted from a megaphone into symmetrical tubes of one top path and one bottom path. The top and bottom paths are initially identical, but the top path can be lengthened. a. Why is the interference initially constructive? b. How far do you have to raise the top part of the tube to achieve destructive interference in m?  

Answer 1

Initially both sound (through top path and which through bottom) path travel equal path Hence, there is zero path difference between both sound wave. They interfere constructively. For destructive interference Path difference = (2n - 1) lambda/2 lambda -wave length For 1st destructive position n = 1 Path draft = lambda/2 If top tube is raised up by x then change in length of path will be 2x middot Hence, Path difference = 2x 2x = lambda/2 x = lambda/4 = > /gamma (4) = 340/550 times 4 because 340 speed of sound in air x = 0.154m