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Homework Help: FluX Density

  1. Jan 12, 2009 #1
    1. The problem statement, all variables and given/known data

    Loop like an "O" with current moving to the left
    Diameter = 8cm
    Current = 15A

    2. Relevant equations

    B(flux density)=F(magnetic flux)/A(area)
    B=H(magnetic field strength)*Permeability
    H(magnetic field strength)=I(current)/A(area)
    L(inductance)=Ioda(magnetic flux)/I(current)
    Ioda(magnetic flux)=V(velocity)xT(time)

    3. The attempt at a solution

    Area = 50.24 = (3.14 *(42))
    Magnetic Field Strangth = .299 or .3 = (15/50.24)

    From this point I am lost because it appears to me that I am missing a key part to finish the equation. If I can find out the time or the charge then I can do some substitions and find the answer the equation. Can anyone point me in the right direction?

    These are the possible answers:

    1. 1.68 x 10^-5 Wb/meters squared
    2. 2.36 x 10^-5 Wb/meters squared
    3. 1.68 x 10^-4 Wb/meters squared
    4. 2.36 x 10^-4 Wb/meters squared
    5. 2.87 x 10 Wb/meters squared
    Last edited: Jan 13, 2009
  2. jcsd
  3. Jan 12, 2009 #2
    That second equation might come in handy.
  4. Jan 12, 2009 #3
    That en lies my problem...

    For that equation, I need to find permeability!
    To find permeability I need to find inductance
    To find Inductance I need to find magnetic flux
    To find magnetic flux I need to find velocity and time!

    How am I to find 2 items to which I am unable to derive a possible answer for?
  5. Jan 12, 2009 #4
    can no one show me what it is that I am missing in this problem?
  6. Jan 12, 2009 #5


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    Homework Helper

    Isn't this just the Biot-Savart law? That should be all you need. You have too many equations.
  7. Jan 12, 2009 #6
    Well I was given no equations to work with because i missed this day in class and im playing catch up so I am lost. These were the "relevant" equations that I could find. Im gonna have to look up Biot...appreciate the possible direction point!
  8. Jan 13, 2009 #7
    After doing some more investigation, I tried another avenue but to no avail.

    Permeability = 4Pi x 10^-7 H/m (IN A VACUUM)

    B(magnetic flux) = H(magnetic field strength) * permeability
    B = .3*(4Pi x 10^-7)
    B = 3.768 x 10^-7

    But it is not the answer according to my instructor...he gave me a list of options as show above but I cant seem to get there. Anyone?
  9. Jan 13, 2009 #8

    B = permeability x current / 2 x radius

    B = (4Pi x 10^-7) x 15A / 2 x (.04 meters)

    B = 2.355 x 10^-4 (rounded off = 2.36 x 10^-4)
  10. Jan 13, 2009 #9
    B= Permeability x Current / Area

    2 x radius looks strongly like a diameter rather than an area
  11. Jan 13, 2009 #10
    Yeha im not exactly sure how any of this works because I missed the last 2 classes and im playing catch up and it sucks but the list of equations that I originally found were the ones I listed and they didnt help me in anyway but after doing some reading I found the equation that I used in my last post and that gave me the answer I was looking for so I have no clue how these equations supposedly tie in together but my instructor said my answer was correct so Im not complaining about that...just sucks that I can't figure out how this all ties in together
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