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: Magnetic field at the center of a loop

  1. Feb 19, 2015 #1
    1. The problem statement, all variables and given/known data
    A conductor consists of a circular loop of radius
    R = 14.4 cm
    and two long, straight sections as shown in the figure. The wire lies in the plane of the paper and carries a current
    I = 1.60 A.
    Find the magnetic field at the center of the loop.

    2. Relevant equations
    biot-savart law

    3. The attempt at a solution
    I know I need use biot-savart law to get the field created by the loop, which is giving me 8.77 uT. This is apparently within 10% of the correct answer.
    Do i need to find the current from the straight part of the wire too (superposition)?

    I'm just not sure how to do this / what equations to use to do this?

    Attached Files:

  2. jcsd
  3. Feb 19, 2015 #2


    User Avatar

    Staff: Mentor

    Yes. And superpostiion is an excellent idea.
    You should have an expression for the magnetic field at a given distance from a current-carrying wire...
  4. Feb 19, 2015 #3
    thats where i'm confused.

    shouldn't i use B = (uI)/(2 pi r) ?
    4pi x 10^-7 x 1.6A / 2 pi x .144m ? this gives me 2.22 uT which when added to the 8.77 is out the the correct range
    Last edited: Feb 19, 2015
  5. Feb 19, 2015 #4


    User Avatar

    Staff: Mentor

    2.22 μT looks right for the straight wire. But the loop contribution looks a bit high to me. Can you show the details of your work there?
    No, the expression gives the field magnitude, not a differential element. The integration was already done in deriving the expression.
  6. Feb 19, 2015 #5
    Ahhhh thank you! my mistake was in the calculation for the loop! i left the 4pi in place when using u/4pi

    hahaah that was dumb. but thank you, i got the right answer. it's 9.20 uT!

Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted