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Please help me

  1. Jun 17, 2005 #1
    Please help me ....

    Hi friends I have some problems and also I have an exam the day after tomorrow ....
    Please help me... :confused:
    1) There is a charge line with a length of infinite , and charge density of (K) and distance of (d) from center of a conductive cylinder which is attached to the earth , What is the capacity of this system as a capacitor ?

    Unfortunatly I can't draw the picture of problem here ... I don't know what should I do...?
    I can scan it and Email you if you want...!?
    If your answer needs some drawings you can Email the answer to me : Aziy2003@ yahoo.com
    Thanks ... :smile:
  2. jcsd
  3. Jun 17, 2005 #2


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    Staff: Mentor

    If the line and cylinder are infinitely long, the capacitance will be infinite.

    If the cylindrical capacitor is finite in length, the capacitance C = Q/V. The Q will just be the charge density per meter multiplied by the length in meters. The voltage difference V is related to the radii of the inner and outer conductor of this coaxial capacitor. Look for an example calculation for the "Capacitance of Coaxial Transmission Line" to see how you work out the voltage difference V. In my old Applied Electromagnetics text by Plonus, it's in section 5.5.

    Hope that helps.
  4. Jun 17, 2005 #3


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    Homework Helper

    Are you looking for the capacitance per unit length, CL=(Q/V)/L? This can be found by looking at the capacitance of a section of the capacitor of unit length (L=1). Q is the charge on the wire for this piece, and V is found by integrating E.dl from the wire a point on the cylinder.
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