Doing a school paper right now, and would appreciate any answer. Please Register or Log in to view the hidden image! I have read in some places that, for two waves, when there is a difference in the path length that is equal to a wavelength, constructive interference will occur. The amplitude of the wave that results is larger than either of the waves that created it—the light will brighten, sound gets louder, etc... Does the difference in path length always have to be equal to a wavelength for constructive interference to occur? Here the waves have the same wavelength and amplitude, but they are not perfectly parallel to each other: http://images.google.co.uk/imgres?i...&hl=en&rlz=1C1GGGE___GB351&sa=N&start=18&um=1 Constructive interference can occur in this case?