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Formation of surface charge densities on wires in simple DC circuits

  1. Oct 4, 2013 #1
    Currently using resources like:
    http://www.matterandinteractions.org/Content/Articles/circuit.pdf [Broken]
    http://www.phy-astr.gsu.edu/cymbalyuk/Lecture16.pdf [Broken]

    I don't seem to understand why the surface charge densities shown in the pictures are stable. I understand that the densities shown create constant electric fields which drive the current, but not why the surface charges themselves are not subjected to movement.
    Last edited by a moderator: May 6, 2017
  2. jcsd
  3. Oct 5, 2013 #2

    Jano L.

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    They may move slowly along the surface. The only requirement is that there is always some charge to produce the electric field in the wire, and to do that, they do not need to be static.
  4. Oct 5, 2013 #3
    Oh ok, I think I understand. So is the charge distribution at any particular time representative of the electric field at those positions? I.e. in areas of high charge distribution is there a lesser electric field and areas of low charge distribution a greater electric field (electric field operating on surface charges NOT the inside ones in the wire). What I am getting at is: that there is less likely to be more charges at areas of high electric field, etc.

    Thanks for reply
  5. Oct 19, 2013 #4

    Jano L.

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    I think it is the opposite; in order to produce higher electric field in the metal point P, there has to be more charges close to this point P on the surface.
  6. Oct 21, 2013 #5


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    The Sherwood paper is interesting because it seems to have been produced in response to a very 'combative' attitude from present day students, to matters that confuse them. He has clearly thought about many of the niggles that students have when approaching the topic of Electricity and has addressed many of the problems very positively and thoughtfully. (The word 'indulgent' springs to mind.)

    The fact is that you need to approach every problem and situation at an appropriate level. (There are 'shells' of understanding in all Science). Circuit problems are nearly always best dealt with by assuming there is no resistance in wires, that the PD is zero and the route taken by the wire is irrelevant. A connecting wire with no (or very low) resistance can be treated in much the same way as a roller coaster track (in a vacuum etc.). In both cases, the energy loss is zero, whatever the path of the wire or the peaks and dips in the track. Ideal roller coaster cars would arrive at the bottom at the same speed, whatever route they took.
    Imo, there is little point in worrying about the local charge distribution (except in a very arm-waving way) unless you are going the whole hog and also consider the Capacitance and Inductances involved.
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