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Complex Dielectric Constant Question

  1. Mar 11, 2008 #1

    I'm trying to follow along in my Solid State Physics book, but I'm getting hung up on an equation for the complex dielectric constant.


    Multiply through by the definition of the complex conductivity, so that we get something in the form of [tex]\epsilon_r=\epsilon'_r+j\epsilon''_r[/tex]


    [tex]\epsilon'_r[/tex] is [tex]\epsilon_L/\epsilon_0 + \sigma_0\tau/\epsilon_0(1+\omega^2\tau^2)[/tex]

    What, exactly, is [tex]\epsilon_L[/tex]? Is it just the old value of the dielectric constant before we introduce this complex stuff (So, a function of [tex]\omega[/tex])? The book doesn't really elaborate.
    Last edited: Mar 11, 2008
  2. jcsd
  3. Mar 18, 2008 #2


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    Homework Helper

    yep. it is just convenient to put everything into a "complex" dielectric function. A really good book on dielectrics that I would recommend is called (I think) "Theory of dielectrics" by Frolich. One does not need to introduce a complex dielectric function if one does not want to... as usual it is just convenient... the fact that there are "two" dielectric functions (i.e., two components [itex]\epsilon^'[/itex] and [tex]\epsilon^{''}[/tex]) is because the response of the system can be out of phase... An external (real) electric field with time dep cos(wt) induces response like Acos(wt)+Bsin(wt) and the coefficient of the sin term is jsut like the imaginary part of the dielectric function. cheers.
  4. Mar 20, 2008 #3
    what does the subscript "L" mean, anyway?
  5. Mar 20, 2008 #4
    From what I understand, it means the effect from only the positively charged cores (Hence, L for Lattice).
    Last edited: Mar 20, 2008
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