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Homework Help: 1 dimensional charge distribution

  1. Feb 4, 2008 #1
    1. The problem statement, all variables and given/known data

    (Lead in to question:

    "Assume that charges +q, -3q, 2q lie at positions -2a, 0, +2a along the x-axis respectively.")

    I've calculated dipole/quadrupole moments about the origin as well as the exact potential at x=+10a, however I'm confused by this next part to the question:

    Show that, for a 1 dimensional problem,

    d(1/R) / dx = -1/x²


    d²(1/R) / dx² = 2/x³

    where R is the distance between a lab fixed point x and an arbitrary origin x0.

    Can anyone suggest a method of tackling this??
  2. jcsd
  3. Feb 4, 2008 #2

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    I am at a loss to understand what this has to do with charges.

    R has been defined to be equal to x.

    So, d/dx(1/R) = d/dx(1/x) = -1/x^2 etc.
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