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Gaussian Problem

  1. Feb 25, 2010 #1
    1. The problem statement, all variables and given/known data

    A thin cylindrical shell of radius R1 = 5.0 cm is surrounded by a second cylindrical shell of radius R2 = 9.0 cm, as in the figure. Both cylinders are 5.8 m long and the inner one carries a total charge of Q1 = +4.2 µC and the outer one carries a total charge of Q2 = -2.4 µC. (Assume the positive direction is away from the axis.)

    a) r = 1.5 cm

    (b) r = 5.5 cm

    (c) r = 11.5 cm

    2. Relevant equations

    E *Da = Qenclosed/Epsilon

    point charge = 1/4pi epsilon * Q/r^2

    3. The attempt at a solution

    a) radius is smaller than the radius of the first shell, so it's EF = 0
    b) i've tried using E = Q / 4pi *epsilon *r^2, but i keep getting the wrong answer = 12.4e6 N/C
    c) I think I should add the charges together (-2.4 + 4.2 = 2uC) and use the above equation, but I am at a loss.

    I keep trying to find the answers to these last 2, but can't seem to get it right.
  2. jcsd
  3. Feb 25, 2010 #2
    do you need to find the E-field at the given r's, at the midplane of the cylinders?
  4. Feb 25, 2010 #3
    "For points far from the ends of the cylinders, determine the electric field at the following radial distances from the central axis."

    yes sorry forgot to include that!!!!!!!
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