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 of long parallel straight wires

  1. Mar 14, 2010 #1
    1. The problem statement, all variables and given/known data
    Two infinitely long parallel straight wires carry currents in the +- z direction as shwn in the figure below. Each wire is located on the x-axis a distance of a from the origin.

    a) Determine B as a function of y along the line x=0
    b) Sketch a graph of B vs. y along the line x=0, including all values of y.


    2. Relevant equations
    B=u0I/2PiR


    3. The attempt at a solution
    for part a i get u0I/PiR
    for part b as y increases, B decreases because they're inversely related?
     
  2. jcsd
  3. Mar 14, 2010 #2

    Redbelly98

    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper

    Not quite. It looks like you're calculating B at the origin (x=y=0) only, but you need to find B all along the y-axis, as a function of y. So you should get some expression that has y in it.

    For this, you'll need to get part (a) done correctly first, then you can sketch the function you get for (a).
     
  4. Mar 14, 2010 #3
    well if one current is flowing in the +z direction and one is flowing in the -z direction the magnetic field is the following:

    B=μI/2∏ {[(-y/(x-a)²+y²)+(y/(x+a)²+y²)]ihat + [(x-a/(x-a)²+y²)+(x+a/(x+a)²+y²)]jhat

    If we let x equal 0 and reduce, we get B = μIa/∏(a²+y²)

    I just know this from the answer in the back of my book, and I have no idea how they get it. :(

    From this equation you can deduce the graph. As y goes to infinity it seems as if B goes to zero. Correct?
     
    Last edited: Mar 14, 2010
  5. Mar 15, 2010 #4

    Redbelly98

    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper

    How about B due to a single wire, do you know that?
    Yes.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Magnetic field of long parallel straight wires
Loading...