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Homework Help: Transmission Line - Electrodynamic Calculations

  1. Apr 18, 2010 #1
    Two very large parallel conducting plates of very large length [tex]l[/tex], and width [tex]w[/tex] are separated by a distance [tex]d[/tex]. A current [tex]I=Jw[/tex] flows to the right in the lower plate and to the left in the upper plate. Each of the two currents produces a magnetic field [tex]\frac{B}{2}[/tex] between the two plates.

    (a) Show that the total field between the plates is [tex]B=\mu_0 J[/tex] via Ampere's Circuital Law.

    (b) Find the flux [tex]\phi[/tex] and the self inductance per unit lenght, [tex]\frac{L}{l}[/tex] for this arrangement.

    (c) Find the capacitance per unit length, [tex]\frac{C}{l}[/tex].

    (d) Find [tex]\sqrt{\frac{L}{C}}[/tex] in terms of [tex]\mu_0, \epsilon_0[/tex] and geometrical factors

    My Attempt at Solution
    Part (a) is confusing as I have not used the circuital Law for rectangular geometry. I know that Ampere's Law is given by:

    [tex]\oint_C \mathbf{B} \cdot \mathrm{d}\boldsymbol{\ell} = \mu_0 I_{\mathrm{enc}}[/tex]

    But am confused as to how to apply it as it is not circular geometry.

    In part (b) I know that:

    [tex]\phi=BA[/tex]

    But am not sure as to what area to use, since we know B per part (a)

    Solving for flux leads us one step closer to finding the self inductance which is:

    [tex]L=\frac{N\phi}{I}[/tex]

    But again, I do not know what value to substitute in for [tex]N[/tex].

    I am pretty sure I can find the capacitance per unit length per (c), and then (d) is a matter of combing (b) and (c) so that would be self explanatory. Could somebody help me get this thing started? Please keep in mind that I have a very elementary understanding of this material.

    Thanks.
     
  2. jcsd
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