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Homework Help: Coaxial Cable Inductance

  1. Jan 14, 2014 #1
    A coaxial cable is modeled as a long thin cylindrical shell with radius b concentric with a solid wire of radius a (the wire is inside the shell). Calculate the inductance of a length l of this cable.

    (Example 32.5 Here) ---> https://echsphysics.wikispaces.com/file/view/APPhysicsCH32.pdf

    the solution in my textbook is as follows: take a thin rectangular slice between the inner wire and the outer shell. If we assume that the outer shell and the inner wire are connected at the two ends of the cable, that rectangular slice can be imagined as a very long loop (with length l) in an solenoid. We get the flux through this long rectangular slice, then the inductance is just L=ϕ/I

    My question is: By definition, the inductance of a solenoid is L=Nϕ/I where is the number of loops. Now if we considered the rectangular slice to be a loop among many that form the coaxial cable, shouldn't the inductance be L=(2∏b)ϕ/I or something? shouldn't there be term equivalent to the N in the solenoid inductance equation because the magnetic field is passing through many of these long rectangular slices?
  2. jcsd
  3. Jan 15, 2014 #2


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    In the solenoid, the individual loops are in series. So, the emf's of the loops add together.

    In the cable, if you choose two different rectangular slices you will get an emf for each slice. But are these slices in series or parallel?
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