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Cant understand this double integral

  1. May 5, 2009 #1
  2. jcsd
  3. May 5, 2009 #2


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    1) Do you understand the meaning of the sum a couple of lines above it?
    [tex]k\sum_i \Delta q_i \sum_j \Delta q_j \frac{(\vec{r}_j - \vec{r}_i)}{(\vec{r}_j - \vec{r}_i)^3}[/tex]

    2) Do you understand why the sum is equivalent to the integral, when the number of charges is very very large?
    [tex]k\int_0^L \lambda \mathrm{d}l_1 \int_{2L}^{3L} \lambda \mathrm{d}l_2 \frac{1}{(l_2 - l_1)^3}[/tex]
  4. May 5, 2009 #3
    the sum is like Coulomb law but what is the meaning
    of sum from i and sum from j

    i dont know why the this sum equals this integral
    i know that integral is a sum too
    bu thy look different
    there is no i and j in the integral
    no L in the sum
  5. May 6, 2009 #4
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