Find a waves length given the electric field?

[Eats Dirt]

Homework Statement

an electro magnetic wave has an electric field given by E= (3.1x10^5 v/m)*khat*Cos[ky-(12.65*10^12 rad/s)t]

Homework Equations

k = 2pi/(lambda)

The Attempt at a Solution

I do not know what to sub in for y and t or how to set the equation equal to something so i can solve. So I am pretty much stuck.

 

[gneill]

This is a traveling wave so its amplitude is a function of position and time. At any given instant of time (suppose you cold freeze time), then the amplitude would look like a cosine curve fixed in space.

On the other hand, if you choose a fixed location (y) then the amplitude at that location will vary according to a cosine function of time, the wave moving through that location at the speed of light. You can pick ANY location along the line of the wave and this will be true. What do you think might be a convenient location? What's the equation for the signal at that location?