# Basic Optics Question. (wave front)

1. Apr 23, 2007

### bumclouds

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!!!!

2. Apr 25, 2007

### Mentz114

Here's a hint : the velocity of the wave described is $$\frac{\omega}{k}$$