1. The problem statement, all variables and given/known data Consider a string that admits waves with velocity v. Near the origin, i.e. in the interval -a < z < a, the string has a different weight, and as a result a different propagation velocity u. The amplitude of the reflected and transmitted wave are proportional to the amplitude of the incident wave. Therefore it is customary to definene the coeffcient of reflection, R, and of transmission, T, as the ratio of the absolute squared amplitudes: R = |AR2/AI2| And T = |AT2/AI2| Calculate R and T, and the corresponding phase shifts δR and δT. 2. Relevant equations I don't know exactly what is used here, but I suppose the wave equation is essential here. 3. The attempt at a solution I can't really think of how to do this. You'd think that the wave 'enters' at the first knot, of which a part is reflected and then a part is transmitted, and the same happens at the second knot. So a part of the wave gets 'stuck' between the knots, a part is transmitted through the entire thing, and a part is reflected off of the first knot. Conceptually it is similar to the finite square well from quantum mechanics (or the opposite of a well, that's not specified), but I don't know how to translate this to actual wires.