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Homework Help: Line Image of a Charged Cylinder

  1. Feb 23, 2014 #1
    1. The problem statement, all variables and given/known data
    A long conducting cylinder bearing a charge [itex] \lambda [/itex] per unit length is oriented parallel to a grounded conducting plane of infinite extent. The axis of the cylinder is at distance [itex] x_0 [/itex] from the plane, and the radius of the cylinder is [itex] a [/itex]. Find the location of the line image, and find also the constant [itex] M [/itex] (which determines the potential of the cylinder) in terms of [itex] a [/itex] and [itex] x_0 [/itex].

    3. The attempt at a solution
    My instructor is giving us problems from a different book than we are using in class and there are some gaps in the material covered. That said, we haven't covered anything but point images (i.e., no "line images"). It seems to me that the location of the image would be at a distance [itex] -x_0 [/itex] on the other side of the plane by symmetry. Is this correct? And I have no idea how to find [itex] M [/itex]. Does anyone have any suggestions?
  2. jcsd
  3. Feb 23, 2014 #2
    Anyone? Am I correct in thinking that the image is on the other side of the plane? Any hints on how to to find [itex] M [/itex]?
  4. Feb 23, 2014 #3


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    The line image is on the other side, but not at a distance ##x_0##. The problem is rather involved, so you have some work cut out for you. You might start with finding some references on the method of images.

    http://www.ece.mcmaster.ca/faculty/nikolova/4FJ4_downloads/tutorials/T02_CircuitParametersTLs.pdf [Broken] I found that contains some discussion of the type of geometry in this problem. In fact, if you can follow the material starting on page 8, I believe you should be able work out the solution.
    Last edited by a moderator: May 6, 2017
  5. Feb 24, 2014 #4
    Thanks, that does look like the geometry of this problem. I think the ratio [itex]\rho_1/\rho_2[/itex] is the constant [itex]M[/itex] it's asking for but I'm not sure how the potential values were found. I will study it some.
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