1. The problem statement, all variables and given/known data A wave at the origin expands outwards passing the points (.01, .03, .02) and (-.01, .015, .025). This wave has a wave speed, V_w = 346 m/s and frequency = 13100 HZ. What is the phase difference between these two points? 2. Relevant equations v = (wavelength)(frequency) Phase Difference = 2pi (delta x) / Wave length 3. The attempt at a solution I attempted to use the following: [(distance between points using 3D formula)/(wave length)] * 2pi = phase difference. This was in correct. I am gonna guess that it's because "Phase Difference = 2pi (delta x) / Wave length" is for a wave in one dimension. My question is how does the phase difference change in 3 dimensions? I attempted to use the surface area of a sphere but it also failed. Something is quite wrong.