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Gauss's Law and flux

  1. Jul 3, 2006 #1
    Ok guys, these are just questions from our book(like critical thinking type).....she said to be able to understand these, for the upcoming test. I'm not sure I fully understand them(if at all).

    1. If a closed surface surrounds a dipole, the net flux through the surface is zero. True or False?


    2. If the net flux through a closed surface is zero, then there can be no charge or charges within that surface. True or False?


    I think the equation to find flux is Gauss's Law, which says E=Q(enclosed)/E(knot). With Q being a negative number(dipole), then I'd say the flux can't be zero.

    Along with what I just said, then if Q=0, then there can not be any flux within that surface.....right?

    Thanks guys!!!
    Brad

    Oh, one more question. Are Equipotential lines vectors? I'm thinking they are, but need to know to figure a question.
     
  2. jcsd
  3. Jul 3, 2006 #2

    Doc Al

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    What makes you think Q (total charge?) is negative for a dipole?
     
  4. Jul 3, 2006 #3
    Well I'm not sure, I guess that is just what I thought. I don't really understand the whole dipole thing(even in chemistry I struggled). Isn't it a negative charge, that will go towards a postive charge? Or, how do I figure Q for the dipole?
     
  5. Jul 3, 2006 #4

    Doc Al

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    An electric dipole consists of two opposite charges with a separation between them; the net charge is zero.
     
  6. Jul 3, 2006 #5
    So then with that information, I'd say that Q=0, thus the flux is 0. So, it is true.

    For the second one, if a dipole is considered a charge....then I'd say it is false.

    Also Doc Al....can ya help me with the vector question, so I can start working on it.....are those equipotential lines vectors??? I can't find it anywhere in my book that says they are(which might mean they aren't), but I was thinking they were for some reason.

    Thank you again!!
     
  7. Jul 3, 2006 #6

    Doc Al

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    Both correct.

    Hint: Does an equipotential line (surface, actually) have a direction?
     
  8. Jul 3, 2006 #7
    No I don't think they do actually have a direction, as far as I know. They aren't like field lines which go from + to -. I think basically they just run perpendicular to field lines, in no general direction. So, no they aren't vectors then.
     
  9. Jul 3, 2006 #8

    Doc Al

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    You are correct.
     
  10. Jul 3, 2006 #9
    Thanks a lot Doc...I appreciate every bit of it!!!!
     
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