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Find magnitude of the magnetic field

  1. Jul 26, 2009 #1
    1. The problem statement, all variables and given/known data

    A wire carries a current of 30A along the x-axis from x = 0 to x = 3.0 cm. Determine the magnitude in uT of the magnetic field at the point y = 4.0 cm on the y-axis.


    2. Relevant equations

    dB = (u/4pi) ((Ids x r)/r^2)

    3. The attempt at a solution

    We tried using this formula, but it didn't work. We are lost. Please help! Be descriptive if you can.
     
  2. jcsd
  3. Jul 26, 2009 #2

    rl.bhat

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    Re: Magnetism

    If you take a small element dx on x-axis at a distance x from the origin, its distance from a point on the y-axis is sqrt(x^2 + y^2)
    Now (dx)xr = dx*sinθ, where r is the unit vector along r and θ is the angle between r and y-axis.
    sinθ = x/sqrt(x^2 + y^2)
    Substitute these values in dB and take the integration from x = 0 to x = 4
     
  4. Jul 26, 2009 #3
    Re: Magnetism

    We don't understand how we're supposed to integrate. Isn't there an R^2 in the bottom?
     
  5. Jul 26, 2009 #4

    rl.bhat

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    Re: Magnetism

    Yes. It is there.
    B = μο/4π*I*Intg[ sinθ*dx/( x^2 + y^2 )
    If you substitute the value of sinθ,the expression becomes
    B = μο/4π*I*Intg[ x*dx/( x^2 + y^2 )^3/2
    Now find the integration and substitute the limits.
     
  6. Jul 26, 2009 #5
    Re: Magnetism

    Can you write out what would be the exact (B=) equation?
     
  7. Jul 27, 2009 #6

    rl.bhat

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    Re: Magnetism

    B = - μo/4π*I/sqrt(x^2 + Y^2)
     
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