1. The problem statement, all variables and given/known data E=Emax.sin(ωt-kx) describes the electric field of a monochromatic plane wave travelling in the x-direction. Verify that a plane which is perpendicular to the x-diretion and moves along the x-axis at the same speed as the wave is a wave front. 2. Relevant equations E=Emax.sin(ωt-kx) 3. The attempt at a solution A "wave front" is a surface where the phase is always the same. -----|-------------------|----------> x-axis ___x1,t1______________x2,t2______ At x1, t2 and x2, t2 must have the same phase which is in the brackets of sin() in "relevant equations". so.... ωt1-kx1 = ωt1-kx2 and I'm guessing since the speed is the same at both points x1/t1 is equal to x2/t2 and we substitute those in or something?? I dunno I've thought about this alot and I'm very stuck!!!!