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Homework Help: Maths notation

  1. Jul 21, 2008 #1

    Defennder

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    This is probably a dumb question but what does the circle through the integral sign mean?
    [tex]\oint[/tex]

    I was thinking perhaps it could denote either the line integral over a closed curve, or the surface integral over a closed surface, depending on the context. But it seems the textbook I use employ that notation even when the line/surface integral is not over a closed curve/surface.
     
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  3. Jul 21, 2008 #2

    HallsofIvy

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    Yes, that symbol means the integral over a closed curve. I've never seen it used for the surface integral over a closed surface but I guess it could be. I would be very surprised if a textbook used that to indicate an integral over a curve that was NOT closed. Could you give an example of that?
     
  4. Jul 21, 2008 #3

    Defennder

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    Ok this is from the 7th Edn of Engineering Electromagnetics by William Hayt and John Buck, pg 212 in the chapter on time-invariant magnetic fields:

    I suppose that it might be explained that the current I would be flowing in a closed circuit and hence a closed path. But what is the interpretation of [tex]\oint[/tex] as applied to surface integrals? Must it be a closed surface?
     
  5. Jul 21, 2008 #4
    I've seen that in Gauss's Law:

    [tex]\oint E\! dA = Q / \epsilon_o[/tex]

    And, yes, to my understanding it must be a closed surface.
     
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