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Homework Help: Visualization of a wire & magnetic field

  1. Apr 19, 2004 #1

    I'm having trouble visualizing the way to calculate magnetic flux inside a wire and I was hoping someone here could help me.

    [tex]\Phi_B = \oint B \cdot dA[/tex]

    Inside a wire, using ampere's law, I got:

    [tex] B = \frac{\mu_0 i}{2\pi}\frac{r}{R^2} [/tex]

    And that's where I get stuck. http://img23.photobucket.com/albums/v68/AngelOfMusic/wire.jpg" [Broken] of the wire, it seems that B is perpendicular to dA everywhere.

    In the book's solution, they had this perspective of the wire:

    http://img23.photobucket.com/albums/v68/AngelOfMusic/wire2.jpg" [Broken] And it suddenly makes sense.

    I was just wondering if someone could point out to me how the two diagrams relate? I'm having trouble going from one perspective to the next.
    Last edited by a moderator: May 1, 2017
  2. jcsd
  3. Apr 19, 2004 #2
    AngelofMusics said: "I'm having trouble visualizing the way to calculate magnetic flux inside a wire...."

    You don't really calculate flux "in" something; you calculate flux through a surface. The magnetic flux through the surface of a cylindrical current carrying wire is zero. But I'm not sure why you want to know this.
  4. Apr 20, 2004 #3
    I should have been more clear. I'm calculating the magnetic flux through a wire in a set up where there are two wires parallel to each other. The solution manual says:

    A question, though: Under what circumstances is the magnetic flux through a wire zero? It seems from the book's explanation that it shouldn't be zero at all.
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