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Homework Help: What is the magnitude of the current density across A1 ?

  1. Nov 3, 2009 #1
    1. The problem statement, all variables and given/known data

    The figure represents a section of a circular conductor of nonuniform diameter carrying a current of 5.00 A. The radius of cross-section A1 is 0.400 cm.

    2. Relevant equations

    (a) What is the magnitude of the current density across A1 ?
    (b) If the current density across A2 is one-fourth the value across A1, what is the radius of the conductor
    at A2 ?

    3. The attempt at a solution

    J=I/A= 5.00A/pi(.004)^2=99,472.8 A m^2
    Could someone help please? I am doing this the right way?
  2. jcsd
  3. Nov 3, 2009 #2


    User Avatar

    Staff: Mentor

    Looks correct so far, except for the units of your answer -- should be A/m^2. You did the right thing in the division, just left out the "/" in the final answer's units.
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