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Homework Help: Sphere potential.w

  1. Jan 20, 2009 #1
    1. The problem statement, all variables and given/known data

    A conducting sphere with radius a = 0.31 m has a net charge Qa = +4 µC. A thin, non-conducting spherical shell of radius b = 0.86 m surrounds the sphere and is concentric with it. This shell has a net charge Qb = +1.5 µC distributed uniformly over its surface. The electric potential at infinity is zero.

    (a) Calculate the electric potential at a radial distance of 0.4 m outside of the thin shell.
    (b) Calculate the potential at the thin shell.
    (c) Find the electric potential mid-way between the surface of the sphere and the surrounding shell.
    (d) Find the potential at the surface of the sphere.
    (e) Find the potential at the center of the sphere.

    2. Relevant equations

    3. The attempt at a solution

    These are driving me crazy. My work gives me the following answers....
    a) 9*10^9 (4*10^-6+1.5*10^-6/1.57)
    b) 9*10^9(4*10^-6+1.5*10^-6/0.215)
    c) 9*10^9(4*10^-6/0.585+1.5*10^-6/0.86)
    d) 9*10^9(4*10^-6/0.31+1.5*10^-6/0.86)
    e) 9*10^9(4*10^-6/0.31+1.5*10^-6)

    which aren't right when I'm typing them in.
  2. jcsd
  3. Jan 20, 2009 #2


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