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: Ampere's aw-conductor.

  1. Feb 1, 2012 #1
    1. The problem statement, all variables and given/known data
    I have to find the magnetic field inside a long conductor of radius a.


    2. Relevant equations
    Ampere's law.
    ∫B.dl=μIenclosed


    3. The attempt at a solution

    Problem has cylindrical symmetry and B is along θ direction.

    B*2∏r=μIenclosed

    How to find what fraction of current inside the area considered?

    I just saw in a book that it is ∏r2/∏a2.But can't figure out the idea.:(

    I know it is very simple and donno why i forget basics always..:(
     
  2. jcsd
  3. Feb 1, 2012 #2

    vela

    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper
    Education Advisor

    You have a total current I in the wire. Assume it's evenly distributed across the cross-sectional area of the wire. What would be the current density?
     
  4. Feb 2, 2012 #3
    Yeah!now got it.
    Current density is constant.

    Ienc/∏r2= Itotal/∏α2
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook