1. The problem statement, all variables and given/known data In the figure below, sources A and B emit long-range radio waves of wavelength λ = 390 m, with the phase of the emission from A ahead of that from source B by 90°. The distance rA from A to detector D is greater than the corresponding distance rB by 130 m. What is the phase difference at D? The image is at : http://www.webassign.net/hrw/hrw7_35-38.gif 2. Relevant equations Δphase = 2∏L/λ(n2 - n1) dsin(theta) = mλ 3. The attempt at a solution Not really sure what to do I plugged 130m into L and used the given lamda and ignored n2-n1 this did not work, help me. I assume I need to use the above two slit equation but im not sure.