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Homework Help: Magnetic flux on a surface

  1. Sep 9, 2006 #1
    Along a wire (of radius r) a current i is crossed from one.
    Calculate the magnetic flux through the surface S, inner to the wire.

    http://img138.imageshack.us/my.php?image=cilindrodb4.jpg

    I think

    [tex]\phi_b= \int B dS= BS[/tex]

    [tex]B=\mu_0 i/2\pi r[/tex]

    How to calculate S if I have not the length of wire?

    The solution of the problem is
    [tex]\phi_b=\mu_0 i /4\pi[/tex]
     
    Last edited: Sep 9, 2006
  2. jcsd
  3. Sep 9, 2006 #2

    Astronuc

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    Staff Emeritus
    Science Advisor

    If this is a wire 'loop' of radius r, then the length is simply 2[itex]\pi[/itex]r, and the area circumscribed by a circle is given by A = [itex]\pi[/itex]r2.
     
  4. Sep 9, 2006 #3
    Area=S

    S is a rectangular (see image linked) surface, it is not a circle.

    S would be the Area of a rectangular of base R and height=length of wire (infinite)
     
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