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Electromagnetism Unit Vectors

  1. Jun 8, 2015 #1
    1. The problem statement, all variables and given/known data
    I am having difficulty understanding the very first step of the following solved problem (I understand the rest of the solution).

    How did they obtain the expressions for ##\hat{n}## (the direction of polarization), and ##\hat{k}## (the unit vector pointing in the direction of the wave vector)? :confused:


    2. Relevant equations

    ##k=\frac{\omega}{\lambda f} = \frac{\omega}{c}=\frac{2 \pi}{\lambda}##

    ##E(r, t) = E_0 \ cos (k.r - \omega t) \hat{n}##

    ##B(r,t) = \frac{1}{c} E_0 \ cos (k.r - \omega t) (\hat{k} \times \hat{n})##

    3. The attempt at a solution

    What technique did they use to find the expression ##\frac{1}{\sqrt{6}} (\hat{x}+2\hat{y}+\hat{z})## for the unit vector perpendicular to ##x+y+z=0## plane?

    Likewise, how did they get the expression ##\frac{1}{\sqrt{5}} (\hat{y}-2 \hat{z})## for the unit vector parallel to the y-z plane?

    I could not find any explanations in my Linear Algebra textbook. So any explanation would be greatly appreciated.
     

    Attached Files:

  2. jcsd
  3. Jun 8, 2015 #2

    blue_leaf77

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    Where do you get that solution from?
     
  4. Jun 8, 2015 #3
    This was the solution provided by my teacher. I don't understand, where did he get he get the expressions for ##\hat{n}## and ##\hat{k}## from?
     
  5. Jun 9, 2015 #4

    blue_leaf77

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    Well that looks strange to me. If the wavevector should be perpendicular to ##x+y+z=0## plane then this plane must be parallel to the planes of constant phase ##\mathbf{k} \cdot \mathbf{r}=C## with ##C## a constant, in fact this plane is one of them. Which means any plane with equation ##x+y+z=C## is traversed by the beam perpendicularly, and we see the possible unit vector of ##k## that that can form such equation by the dot product with ##\mathbf{r}## must subtend the same angle with all three axes.
    But I would like to hear the other's opinion.
     
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