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: Urgent Magnetic Field Problem Urgent please Help!

  1. Apr 14, 2008 #1
    Urgent Magnetic Field Problem!!! Urgent!!!!!!!!!!please Help!

    1. The problem statement, all variables and given/known data

    a) What is the direction of the net magnetic filed at P due to the currents?
    b) Determine the magnitude of the net magnetic field at P due to the currents.

    A charged particle at point P that is instantaneously moving with a velocity of 10^6 meters/second toward the top of the page experiences a force of 10^-7 Newtons to the left due to the two currents.

    c) State whether the charge on the particle is positive or negative.
    d) Determine the magnitude of the charge on the particle.
    e) Determine the magnitude and direction of an electric field also at point P that would make the net force on this moving charge equal to 0.

    2. The attempt at a solution

    I know the answer to part b). it is 6e-6 T and 4e-7 T.

    i need help with the other parts. i think, for part a), the direction of the net magnetic field is in the -x becuase the direction of the magnetic filed for the 3Amp wire is +z and the direction of the 1A wire is -z but i need help!!!

    THE PICTURE IS ATTACHED.!!!!.!!!!!!!!!!!!!!!!!!!!!!!!!

    Attached Files:

    Last edited: Apr 14, 2008
  2. jcsd
  3. Apr 14, 2008 #2
    can't really help until the picture is approved lol. You should jus take a screen shot of the problem and upload the pic to imageshack or something.
  4. Apr 14, 2008 #3
    do you know who approves the pictures? can someone please tell them to approve the picture???
  5. Apr 14, 2008 #4
    i drew the picture.
    so does that mean that no one can see the picture?

    well i can give you a general description it is like the x and y-axis but is is slanted, although the angles are 90 degrees.
    there is a line going to the x-axis and a line going to the y-axis from point P so basically it looks like a rectangle on top of a almost completely turned x and y-axis. the 3A is on the y-axis and the 1 A is on teh x-axis. the 1.0m line goes from point P to the y-axis and the 0.5m line goes from point P to the x-axis.
  6. Apr 14, 2008 #5
    i wanna help, but i cant quite understand your description. post it to photobucket and host from there.
  7. Apr 14, 2008 #6
    no problem. i think everyone was just waiting for you to post an image, people totally wanna help so no dont worry. :)
  8. Apr 14, 2008 #7
  9. Apr 15, 2008 #8
    omg, dont kill me, but i dont get it. i know someone will though.
    to verify, the velocity is pointing north, the magnetic Force is pointing left... the magnetic field for the 3Amp wire is +z, and magnetic field for the 1Amp wire is -z.......?
  10. Apr 15, 2008 #9
    oh, but for part d...
    F = q v B sin (theta)
    rearrange for q, because you have F and v, and you, yourself found B :)

    after you find q, you can do part e...
    E = F/q
  11. Apr 15, 2008 #10
    wait, what is the value of sin theda????? and what is B?
  12. Apr 15, 2008 #11
    IS theda 90 degrees?
    and i still don't know what B is?
    Last edited: Apr 15, 2008
  13. Apr 15, 2008 #12
    i totally cant even answer you on theta bc the diagram seems to be missing B fields.
    B = magnetic field.

    all i know is F = 0 when charges move parallel or antiparallel to the magnetic field bc sin0 = 0 and sin180 = 0

    i hope someone helps...ill keep checking on this because i want to know the answer too. ps. have you tried posting on answers.yahoo?
    Last edited: Apr 15, 2008
  14. Apr 15, 2008 #13


    User Avatar
    Homework Helper

    Hi physicsbhelp,

    About your answers to part b: they want to know the net magnetic field force that comes from adding the separate magnetic field produced by each wire at point P. Those numbers that you stated, how did you get those? If those were the magnetic fields of the wires then I believe one of them is wrong.
  15. Apr 15, 2008 #14


    User Avatar
    Homework Helper

    Hi physicsbhelp,

    As I said in my last post, I think a good place to start would be with the two numbers you gave to part b. Did you find them using

    B = \frac{\mu_0 I}{2 \pi r}

    If so, I believe you made a calculation error in one of them. Once you have the correct magnitudes of each magnetic field, you'll then need to find the direction of each which will show you how to add them together. The vector sum of those fields will be the answers to a and b.
  16. Apr 15, 2008 #15


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Someone has already given the formula for the magnitude of magnetic field due to an infinite wire carrying a current. Do you know of a method to find the direction of a magnetic field around a current carrying wire?
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook