1. The problem statement, all variables and given/known data Hi all If we look at a harmonic wave with constant amplitude, Ψ(x,t) = Asin(kx-ωt), then a point with constant magnitude (e.g. a crest) moves such that kx-ωt is constant in time. Now we look at a plane wave Ψ(r,t) = Aexp(i[kr-ωt]). Will a point with constant magnitude (i.e. the whole plane) also move such that i(kr-ωt) is constant in time? If yes, then doesn't this mean that the phase for a plane wave is constant for all times?