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Homework Help: Magnetic field

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

    a long straight 6mm diameter conducting wire is carrying a current of 4A.

    1)What is the magnitude of the magnetic field at a point 1mm inside the surface of the wire.

    2)what is the magnitude of the magnetic field at a point 2cm from the centre of the wire

    2. Relevant equations

    using amperes law:
    for part 1 i got 44*10^-9

    and for part 2: 50*10^-9

    I wnt to make sure i have done it right though, becuase it is a past exam question that i dont have solutions for. So if anyone is good at these questions, it would be helpful to check my answers in case i have stuffed up.

    3. The attempt at a solution
  2. jcsd
  3. Nov 3, 2009 #2


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    The answers to both parts are incorrect.
  4. Nov 3, 2009 #3
    how do you calculate current inside the wire? And do you notice units of all parameters when you calculate?
  5. Nov 3, 2009 #4
    what i tried was:

    diameter =6mm. At a point 1mm inside the conducting wire, diameter is 4mm, therefore r=2mm

    using amperes law:


    I{Through}=I∗((πr²)/(πR²)) where R=6mm and r =2mm

  6. Nov 3, 2009 #5
    You wrote diameter = 6mm but then when you put it into eq, you wrote R=6mm.
    Last edited: Nov 4, 2009
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