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: Canceling Magnetic Field between two wires using an external force

  1. Nov 1, 2008 #1
    1. The problem statement, all variables and given/known data
    Suppose that I1 = I2 = 20 A; currents are running opposite each other, and that the separation between the wires is 0.019 m. By applying an external magnetic field (created by a source other than the wires) it is possible to cancel the magnetic field at the position of each of the wires. This external field must point along the vertical direction. What is the magnitude of the external field?

    2. Relevant equations
    B= [(permeability of free space) times (current)]/ [(2 (pie) r)]
    F(from wire 1 to 2)= I2 [(permeability of free space)I1]/[2 pie r] times L
    Permeability of free space is 4 pie times 10-7 Ttimes m/A

    3. The attempt at a solution Working through this a plugged in current and separation between wires into the equation to find B. I got .084 Telsa. I found out this was the wrong answer and thought doubling it would get me the right answer, but it didn't. I wasn't given a radius for the wire so I don't know what to do. Can anyone help me?
    Last edited: Nov 2, 2008
  2. jcsd
  3. Nov 2, 2008 #2


    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper

    From what you wrote, I have no idea what the question is.

    Please write out the problem statement exactly as it was given to you.
  4. Nov 2, 2008 #3
    I have added the question by editing my initial information. If anyone can help me it would be greatly appreciated.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook