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Magnetic Flux Exiting a Cube

  1. Jul 9, 2014 #1
    1. The problem statement, all variables and given/known data

    Here is the prompt: http://imgur.com/FTFz0fZ


    2. Relevant equations

    Magnetic flux = ∫B dot dA

    Net Flux for closed surface = 0


    3. The attempt at a solution

    For part a:
    magnetic flux = (7.74 ^i + 4 ^j + 3 ^k)T * (0.254 m)^2 ^i
    = 7.74 T * (0.254m)^2 m
    = 0.499 Wb

    For part b:
    I'm not really sure. I know that the net flux for a closed surface is 0, so does that mean if 0.499 Wb is exiting from one face that -0.499 Wb would be exiting from the other 5 to make it 0?
    = -0.499 Wb??
     
  2. jcsd
  3. Jul 9, 2014 #2

    Orodruin

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    Assuming the numerical values are correctly computed, what you have done seems reasonable.
     
  4. Jul 9, 2014 #3

    BiGyElLoWhAt

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    Well the total flux would be the sum of the flux from all 6 sides.

    Just out of curiosity is this a webassign problem?
     
  5. Jul 9, 2014 #4

    Orodruin

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    And magnetic fields are conservative, which means that the total flux is zero. This is the property he is using...
     
  6. Jul 9, 2014 #5

    BiGyElLoWhAt

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    I understand that. I'm just saying he could always check it if he was doubtful, which is what I got out of the OP.
     
  7. Jul 10, 2014 #6

    rude man

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    It's not that magnetic fields are conservative. Electrostatic fields are conservative, but the net flux emanating from a volume is zero if and only if there is no charge inside that volume.

    In fact, there is no meaning to calling a magnetic field conservative since moving a charge around a mag. field results in zero work no matter where the start and end of the path is. In a conservative field, the force is derivable from the gradient of a scalar, which is not the case for a mag. field.

    (A few authors do consider the mag. field conservative since the circulation is zero but that is far-fetched.)

    The property he is invoking is ∇*B = 0 i.e. there are no isolated poles in a mag. field that can be stuck inside a given volume. So by the divergence theorem the total mag. flux out of any closed surface = 0.
     
    Last edited: Jul 10, 2014
  8. Jul 10, 2014 #7

    rude man

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    Right.
     
  9. Jul 10, 2014 #8

    Orodruin

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    Indeed, brain freeze. What I meant to say was "divergence free".
     
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