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MyName
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Homework Statement
Show whether or not the following functions satisfies Maxwell's Equations in free space. (That is, show whether or not they represent a valid electromagnetic wave).
[tex]E(x,y,t)=(0,0,E_0 sin(kx-ky+\omega t))[/tex]
[tex]B(x,y,t)=B_0 (sin(kx-ky+\omega t),sin(kx-ky+\omega t),0)[/tex]
Homework Equations
[tex]\nabla \times E=-\frac{\partial B}{\partial t}[/tex]
[tex]\nabla \times B=\mu_0 \epsilon_0\frac{\partial E}{\partial t}[/tex]
[tex]\nabla \cdot E=0[/tex]
[tex]\nabla \cdot B=0[/tex]
The Attempt at a Solution
Starting with the easy two, It is clear that these functions have zero divergence.
Then Ampere's Law gives us that [itex]2B_0k=\mu_0 \epsilon_0 \omega E_0[/itex]
And Faraday tells us that [itex]kE_0=\omega B_0[/itex]
We then elliminate [itex]\frac{E_0}{B_0}[/itex] from these two equations and note that [itex]\frac{1}{\mu_0 \epsilon_0}=c^2[/itex] to find that [itex]\omega=\pm kc\sqrt{2}[/itex]
Up to this point i am fine. The field clearly satisfies maxwells equations aslong as these conditions are met. My problem is that it seems this implies the field pattern travels at [itex]\frac{\omega}{k}=\pm c\sqrt{2}>c[/itex] (the group velocity of the wave, correct?). This obviously can't be right. I do not know if I'm just interpreting the result wrong, or if somehow this field is invalid for some reason despite satisfying maxwells equations. I've been scouring my textbook and the internet for the last few hours and can't seem to find anything explaining my issue, and would really appreciate some help, thanks.