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Homework Help: Electric Potential within coaxial cylinder

  1. Feb 20, 2008 #1
    1. The problem statement, all variables and given/known data
    A long metal cylinder with radius a is supported on an insulating stand on the axis of a long, hollow metal tube with radius b. Thew positive charge per unit length on the inner cylinder is [tex]\lambda[/tex], and there is an equal negative charge per unit length on the outer cylinder. Calculate the potential for r < a; a < r < b; r > b.

    2. Relevant equations
    Va - Vb = [tex]\int[/tex]E.dl

    3. The attempt at a solution
    I really just need help figuring out why the answer for when r < a is:
    The reference point here is b. If we are looking for the potential INSIDE the smaller cylinder with radius a, then why are we only integrating from b to a? Shouldn't it be from b to 0? Or is the potential inside the smaller cylinder constant? Why would that be?
    Last edited: Feb 20, 2008
  2. jcsd
  3. Feb 20, 2008 #2
    Well what IS the potential inside a hollow conductor at equilibrium? The electric field is zero, right? so...
  4. Feb 20, 2008 #3
    The smaller cylinder is not hollow and I don't think its a conductor (and its supported on an insulating stand anyway)... unless being "metal" is synonymous with conductor? E inside a conductor is 0, but I don't think the smaller cylinder is a conductor.
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