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Homework Help: Ring of radius R and uniform charge

  1. May 17, 2012 #1
    1. The problem statement, all variables and given/known data
    At what distance along the central axis of a ring of radius R = 0.200 m and uniform charge is the magnitude of the electric field due to the ring's charge maximum? What is the positive solution for z?

    2. Relevant equations
    E = [itex]\frac{kqz}{(z^2+R^2)^(3/2)}[/itex]

    3. The attempt at a solution
    I know I should differentiate that above equation with respect to z and then set it equal to 0 to get z but i just dont know how to differentiate that ..

    E = [itex]\frac{kqz}{(z^2+R^2)^(3/2)}[/itex]

    the k and the q are held as constants and can be taken out of the differentiation ..

    = kq*[[itex]\frac{d}{dz}[/itex]((z2+R2)3/2]

    isn't [itex]\frac{d}{dz}[/itex]((z2+R2)3/2 = -3z(z2+R2)^(-5/2) ??

    so it would be kq [-3z(z2+R2)^(-5/2)]

    but that doesn't work for when you set it = 0. what am i supposed to be doing that im not
  2. jcsd
  3. May 17, 2012 #2
    never mind .. i got it now!
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