1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Calculating magnetic flux

  1. Sep 7, 2011 #1
    1. The problem statement, all variables and given/known data

    A cube of edge length 0.05m is positioned as shown in the figure below. A uniform magnetic field given by B = (5 i + 3 j + 2 k) T exists throughout the region.


    a) Calculate the flux through the shaded face.

    2. Relevant equations

    [itex]\phi[/itex] = B.A cos [itex]\theta[/itex]

    3. The attempt at a solution

    The area would simply be 0.0025m^2

    I'm having trouble understanding how to get the angle and also how to interpret the given magnitude of the magnetic field, it's a vector quantity.

    I thought at first the way to get the angle was to assume that the surface of the cube could be considered a vector as well, that way it would only have the j component since it's only got a direction in the y-axis.

    Then using the formula for the angle between two vectors, I got 53.5 degrees, though I'm not too sure how to use the given magnetic field value.
    Last edited: Sep 7, 2011
  2. jcsd
  3. Sep 7, 2011 #2


    User Avatar
    Science Advisor
    Homework Helper

    Hi NewtonianAlch! :smile:
    Forget angles, forget magnitude of the field …

    just do the inner product! (dot product)​

    the area can be represented by a vector of magnitude A in the normal direction, so just "dot" that with the field, and that's your flux! :wink:

    (or you can "dot" it with the unit normal, and then multiply by the area … same thing)
  4. Sep 7, 2011 #3
    Hi tinytim,

    Do you mean to say:

    (5, 3, 2)[itex]^{T}[/itex].0.0025 which is (5*0.0025 + 3*0.0025 + 2*0.0025)

  5. Sep 7, 2011 #4


    User Avatar
    Science Advisor
    Homework Helper

    No, (5,3,2).(the unit normal times 0.0025) :smile:

    (btw, you can't write BT.A …

    it's either BTA or B.A :wink:)
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook