# Plasma: Wave and Phase difference

1. Dec 8, 2011

### erogard

Hi,

I need someone to rephrase the question or tell me what it is actually asking for because I am not sure I understand it clearly:

Consider a plasma slab of width L. k_0 is the wave number in a vacuum, and k in the wave number in the plasma, where k satisfies the dispersion relation:
$$\frac{ck}{\omega} = \left( 1-\frac{\omega^2_{pe}}{\omega^2}\right)^{1/2}$$
where c is speed of light, ω the wave frequency and ω_pe the electron plasma frequency.

Question: Determine the phase of the wave at x=L when n=n_e0 = constant, relative to the phase of the wave traveling the same distance L in a vacuum.

Should I start with 2 plane waves, one in vacuum and one traveling through the plasma, where I would assume that the second has a phase phi and determine the latter?

Any clarification would be much appreciated.