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Homework Help: Conducting cylinder

  1. Dec 7, 2006 #1
    1. The problem statement, all variables and given/known data

    a long conducting cylinder with inner radius a and outer radius b carries a current along its central axis. blah blah blah, i found the current density.

    now how do i calculate the area of the cylinder with a hole in it?

    is it A = pi (b-a)^2 OR is it A = pi ( (a+b)/2)^2
     
  2. jcsd
  3. Dec 7, 2006 #2

    HallsofIvy

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    Science Advisor

    Neither one! The area of the base is the area of the larger circle, [itex]\pi b^2[/itex], minus the area of the inner circle, [itex]\pi a^2[/itex], or [itex]\pi (b^2- a^2)[/itex].
     
  4. Dec 7, 2006 #3
    thank you kind sir
     
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