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: Two parallel wires

  1. Jul 7, 2008 #1
    In the picture, two parallel wires carry currents in opposite direction. Where will the magnetic force never be zero?
    http://img154.imageshack.us/img154/4706/31130394mv0.th.jpg [Broken]

    1. you need to know the currents to answer this question
    2. nowhere
    3. part A
    4 part B
    5 part C

    All I know about these two wires for sure is that they will repel each other and so move away from each other. I relaly don't know where the magnetic force will never be zero.
    Last edited by a moderator: May 3, 2017
  2. jcsd
  3. Jul 7, 2008 #2


    User Avatar
    Gold Member

    Do you know the right hand rule? This is the rule that relates the direction of the current with the curl of the magnetic field.

    In this case, for I(1) you point your right thumb toward the right (following the current) and you will see that your fingers curl toward you, so the magnetic field from this wire comes out of the page.

    For I(2), point your right thumb to the left and your fingers curl in, so this B-field goes into the page.

    These two fields will cancel IFF the currents are equal (which would result in two equal fields that are opposite in direction).

    However, since we don't know the currents the answer is (1), you need to know the currents to answer this question.
  4. Jul 7, 2008 #3
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook