- #1
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Homework Statement
I was looking through my notes when I saw the following expression of a plane wave represented as a phasor [tex]A_{0}e^{i(\vec{k}\cdot\vec{r}-\omega t)}[/tex]
Now I can certainly understand a plane wave propagating along a given coordinate axis say, x or z, and the phasor representation of that would simply be [tex]A_{0}e^{i(kx-wt)}[/tex].
But somehow when I'm forced to consider the wave traveling in an arbitrary direction wrt to some fixed coordinate system, I don't understand how that reduces to the equation above (the first latex expression). I suppose it's due to the fact that k and r are both vectors and that k in the 2nd latex expression is a scalar given by [tex]\frac{2\pi}{\lambda}[/tex].
I don't remember ever learning about k being treated as a vector and if so what direction is it oriented in? I searched the internet and found:
http://en.wikipedia.org/wiki/Wave_vector
but apparently the page doesn't explain why it's possible to substitute the expression k.r into the plane wave phasor itself. And why the dot product? I'm guessing that it's because we would then obtain three separate phasors for each x,y,z component, but I still don't see why exactly is it used.
Could someone point me to a textbook or an online resource for clearer explanation?