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!

Homework Help: Two Long Straight Wires Carrying Curent

  1. Mar 18, 2016 #1


    User Avatar
    Gold Member

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

    2. Relevant equations
    B = μ0*i/(2PI*r)

    3. The attempt at a solution
    First of all, if you're looking at this, that means you intend to help me study for my upcoming physics exam on a Friday night. If you fit into this category of people, then god bless your soul.

    I should state that I have all the answers to these, because the solutions are posted - I just want to ensure that I understand the material. Some of the solutions are illegible, but that's not a huge deal.

    So, I understand part a: I use the relevant equation that I typed and replaced 'i' with "i1" and "i2" and replaced 'r' with 'd.' After accounting for unit vectors, the correct answer is:

    B(vector) = μ0*(i1*x(vector) + i2*y(vector))/(2PI*d)

    So, let's start w/ part b: I have no clue what's going on besides that we need to find the force per unit length, which is F3 / L where L is length. The formula sheet equates F3 / L = i3 * B(total). Why is this the case?
  2. jcsd
  3. Mar 18, 2016 #2
    so, what is force on a current carrying conductor in a magnetic field?
  4. Mar 19, 2016 #3


    User Avatar
    Gold Member

    Oops, brain fart - Fm = iL x B, so Fm/L = i3*B(tot). B(tot) is equal to (μ0*√i1^2+i2^2) / (2PI*d), so Fm/L is equal to i3 times this.

    For c, if the angle is to be 45 degrees, then tan^-1(i2/i1) = 45 degrees. This would mean that the ratio of i2/i1 is one to one, so i1 would have to be the same value as i2, which is 40.0 mA. The resultant force vector would be -45 degrees because the force is perpendicular to the B-field.

    I'm confident that these answers are correct. Of course, you can let me know if you see a discrepancy, though. Thanks for your help!
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted