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: Eddy Currents

  1. Jun 29, 2008 #1
    Hi All!

    I am working on the Eddy Currents problem.

    I was to set up the problem and derive some equations for the pivot pendulum with Eddy currents.

    Please see attachment.

    As you see the pendulum swings between max point ( just outside the B field) and enters the B field and then reaches another max just outside the B field.

    The B field is uniform and pointing in the "page"
    Eddy currents are shown.

    How to set it up.

    I did researched the Wikipedia.com and other sources on the internet I checked the book and the class notes too.
    I came to the conclusion that I need help!!!!!!!

    Thanks again ... you guys are great!

    Chris W

    I hope this is enough to set up this problem. If you need dimensions like height and width or length, just use variables.

    P.S. Please see the attachment for the FBD.

    Attached Files:

  2. jcsd
  3. Jun 29, 2008 #2
    what I could conclude so far is that:

    when the pendulum makes that swing the area (A=w*h) of the bottom part of the pendulum is submerged in the B-field while swinging.

    this can be explressed as dA/dt

    vltage generated is = - n d[tex]\phi[/tex]/dt

    and d[tex]\phi[/tex] is changing while the A is outside the B field the the magnetic flux is 0

    when the pendulum make the swing and enters the B field the volatage generated is

    EMF = - N d(BA)/dt


    I am stuck

    any ideas?

    please help


    Chris W
  4. Jun 29, 2008 #3
    I think my question is related to the notes that I have.

    Please see the attachment.

    Chris W

    Attached Files:

  5. Jun 29, 2008 #4
    hmmm anyone ??
    any hints?
    any ideas?
    please... and thanks you
    Chris W
  6. Jun 29, 2008 #5


    User Avatar
    Gold Member

    Hey Chris,

    I don't think anyone can see your attachments yet, as they're still awaiting approval by the forum. Give it some time, and once people can review your attachments I think they'll help you out.
  7. Jun 29, 2008 #6

    Thanks guys.

    Chris W

    Basically it looks like this:
    ------>pivot point
    | / \ |
    | X X / \ X X |<--------region of the B field
    | / \ | pointing into the
    | X 1 / X \ 2 X | screen X
    | _/_ _\_ |
    |X |__| X |__| X |
    |_______________________ |

    the pivot point of the pendulum is on the top

    B field is uniform and constant

    position 1 - the pendulum is outside the B field
    (sorry the PBD don't show that, hard to do it here)
    the eddy forces in the box on the bottom of the pendulum are counterclockwise
    the Fm is pointing to the left
    the v is pointing to the right

    position 2 - the pendulum is outside the B field again on the another side
    (sorry the FDB don't show it that this is the case - but you can imagine what is going on)
    The eddy forces in the box on the bottom of the pendulum are clockwise
    the Fm is pointing to the left
    the v is pointing to the right

    the box on the bottom of the pendulum has dimensions W*H

    If this won't help I guess we have to wait till the attachment will be available

    but thanks again

    Chris W
  8. Jun 29, 2008 #7
    man... this won't work ...

    sorry I was trying to make a FDB using keyboard.... all is massed up!

    let's wait!

  9. Jun 29, 2008 #8
    oh... I think the attachment are available now!!!!
    just on time!
  10. Jun 29, 2008 #9
    Re: Fdb

    I hope you can see the attachments

    now you can see what I was trying to "draw" using the keyboard.... lol
  11. Jun 29, 2008 #10
    hmmmm.... can you see the attachments?

    the FDB for the problem is drawn by hand.

    the class notes attachment is something that I think is needed to set up the problem

    I don't have to solve .

    just set up the equations

    please ... I need help here


    Chris W
  12. Jun 29, 2008 #11
    Hi guys.

    First off I would like to say thanks for the help that I got from all of you!
    you guys rock!

    as for the Eddy current problem.... hmmmm

    I don't know why one is it.???
    is this problem that hard? hmmm wow .................(I didn't expect it!)
    or the explanation is bad?

    please let me know so I know what is going on.

  13. Jun 30, 2008 #12
    I guess the explanation is bad.I don't get your question at all friend.Please bit be a bit more clear by what you mean by 'setting it up'?
  14. Jul 1, 2008 #13
    the pendulum will experience the damping force due to the B field.

    I was wondering how to set up the equation for this problem.

    the effect of the damping force can be seen on this video.

    thank you

    Chris W
    Last edited by a moderator: Sep 25, 2014
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook