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Homework Help: I have a capacitor question need help

  1. Oct 2, 2009 #1
    A 31 m length of coaxial cable has a solid
    cylindrical wire inner conductor with a di-
    ameter of 2.042 mm and carries a charge of
    7.32 μC. The surrounding conductor is a
    cylindrical shell and has an inner diameter of
    6.748 mm and a charge of −7.32 μC.
    Assume the region between the conductors
    is air. The Coulomb constant is 8.98755 ×
    109 N · m2/C2.
    What is the capacitance of this cable? An-
    swer in units of nF.

    What is the potential difference between the
    two conductors? Answer in units of kV

    need help, I tried it but failed to get the right answer
  2. jcsd
  3. Oct 2, 2009 #2
    [tex]C=L\frac{2\pi \epsilon_0}{\ln \frac D d}[/tex]

    D=6.748 mm, d=2.042 mm and L=31m.

    Then use:

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