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!

Magnetic field between 2 parallel wires

  1. Nov 9, 2012 #1
    1. The problem statement, all variables and given/known data
    Sorry. I know this question is on the forum somewhere, but I still don't get it... Thus.

    For parallel wires, at the mid-point of the wires, what is the strength of the magnetic field? Do I use the formula [itex]B=\frac{μi_{1}i_{2}L}{2∏r}[/itex], or is it the sum of
    [itex]B=\frac{μi}{2∏r}[/itex], for both wires? I'm really confused:(

    For example,
    Two parralel wires are 8 cm apart. The magnetic field halfway between them is 300 uT. What equal currents must be in the wires?

    I would use equation no. 1, but it is actually 2x equation (2). Thus I don't really get, how to calculate the magnetic field between 2 parallel current carrying wires? And when to use equation (1)?

    Thank you.

    2. Relevant equations



    3. The attempt at a solution
     
  2. jcsd
  3. Nov 9, 2012 #2

    haruspex

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member
    2016 Award

    For one wire you would obviously use eqn 2. For two wires it will be just the sum of the fields due to each wire, so just use eqn 2 for each and add them up. (Note that the currents must be in opposite directions or the fields would cancel.)
    I don't recognise eqn 1. It doesn't make sense dimensionally. Where did you find it?
     
  4. Nov 9, 2012 #3
    Oh, okay, thanks!

    Uh the 2nd formula is in quite a lot of places actually, though I might have misunderstood it... Places like http://www.cartage.org.lb/en/themes/sciences/physics/electromagnetism/Magnetostatics/MagneticField/Forcesoncurrents/parallelwires/parallelwires.htm [Broken]

    and the attached is the Halliday Textbook... In such a case, what do they mean by the 1st equation? Is it the force acting on one wire or something? Thanks!
     

    Attached Files:

    Last edited by a moderator: May 6, 2017
  5. Nov 9, 2012 #4

    haruspex

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member
    2016 Award

    Yes, it's the force the wires experience from each other, not the field.
    Field at 1st wire = B1 = μ i2/d
    Current in 1st wire = i1
    Force per unit length acting on first wire = B1 i1 = μ i1i2/d
    Force on 1st wire of length L = μ i1i2L/d
     
  6. Nov 9, 2012 #5
    Thank yu very much! Now I get it:D
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Magnetic field between 2 parallel wires
Loading...