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PlezI want your help

  1. May 6, 2009 #1

    pop

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    plez..I want your help :(

    I have HW is Difficult for me

    if any body can help me :(

    Q1:
    1)In a conducting media the wave equation:
    [tex]\Delta[/tex]^2[tex]E[/tex]=[tex]\mu[/tex][tex]\sigma[/tex][tex]dE/dt[/tex]+[tex]\mu\epsilon[/tex][tex]d2E/dt2[/tex]

    has solution of the type E(z, t) = E0 exp [ i (kZ –w t)], where
    [tex]\kappa[/tex]^2 = [tex]\mu\epsilon[/tex] w2 + i [tex]\mu\sigma[/tex] w.
    a) Find explicit expressions for real and imaginary parts of [tex]\kappa[/tex] .
    b)Show that in a good conductor the electric field leads the magnetic field by 45(deg) and find the ratio of their amplitudes. ?


    Q2:
    A monochromatic plane polarized electromagnetic wave
    E(r, t) = E0 sin (k. r – w t) is traveling eastward.
    The wave is polarized with E directed vertically up and down alternately. Calculate E, B and the Poynting vector S provided that the amplitude of the electric field strength is 0.05 V/m and the frequency = 6 MHz. Also, find the <S>?

    plez I wanna the answer. befor friday night

    thanx for all
     
  2. jcsd
  3. May 6, 2009 #2

    gabbagabbahey

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    Re: plez..I want your help :(

    Hi pop, Welcome to PF!:smile:

    As per the forum rules, you need to show some attempt at a solution in order to get assistance here.
     
  4. May 6, 2009 #3

    tiny-tim

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    Welcome to PF!

    Hi pop! Welcome to PF! :smile:

    (try using the X2 tag just above the Reply box :wink:)

    (also, if you use LaTeX, just put tex and \tex at the start and end of each line; and ∇ is \nabla not \Delta :wink:)

    Q1:
    1)In a conducting media the wave equation:
    2E = µ σ dE/dt + µ ε d2E/dt2

    has solution of the type E(z, t) = E0 ei (kZ –w t), where
    k2 = [tex]\mu\epsilon[/tex] w2 + i [tex]\mu\sigma[/tex] w.
    a) Find explicit expressions for real and imaginary parts of [tex]\kappa[/tex] .
    b)Show that in a good conductor the electric field leads the magnetic field by 45(deg) and find the ratio of their amplitudes. ?

    For 1a), just differentiate … what equations do you get? :smile:

    And that should help you with 1b) :wink:
     
  5. May 6, 2009 #4

    pop

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    Re: plez..I want your help :(

    gabbagabbahey:

    thanx
    i read it :wink:
    ____________

    tiny-tim

    hi
    yah I know ....if i do this i will get :
    k2 = [tex]\mu\epsilon[/tex] w2 + i [tex]\mu\sigma[/tex] w.

    but i don't need this i need Eq 9.126 in Ch 9
    in Griffiths. Electrodynamics 3ed :biggrin:
    >> sorry i can't write it :)

    any way thanx alot .....i did it

    _____________

    I still wait to your help in Q2

    :)
     
  6. May 6, 2009 #5

    gabbagabbahey

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    Re: plez..I want your help :(

    This forum supports LaTeX, which should make writing vector equations easier for you. For example, a general monochramitic plane wave is given by

    [tex]\vec{E}(\vec{r},t)=\vec{E_0}e^{i(\vec{k}\cdot\vec{r}-\omega t)}[/tex]

    ....Now, as for your question, I'd start by picking a coordinate system (for example, positive x-direction="East" and "vertical"=positive y-direction) and then write explicitly the polarization unit vector and wave vector and use that to re-write [itex]\vec{E}(\vec{r},t)[/itex].

    Then, use Faraday's Law to calculate [itex]\vec{B}(\vec{r},t)[/itex]. And finally calculate <S>.
     
    Last edited: May 6, 2009
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