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Homework Help: Magnetic Field homework

  1. Oct 19, 2014 #1
    1. The problem statement, all variables and given/known data
    Figure 29-61 shows a cross section of a long thin ribbon of width w = 4.91 cm that is carrying a uniformly distributed total current i = 4.61 * 10^-6 A into the page. What is the magnetic field at a point in the plane of the ribbon at a distance 2.16 cm from its edge?

    2. Relevant equations
    B = ((1.26 * 10^-6)i)/(2*pi*R)


    3. The attempt at a solution
    I tried using the Biot-Savart law:

    0.0491 m + 0.0216 m = 0.0707 m

    ((1.26 * 10^-6)(4.61 * 10^-6))/(2*pi*0.0707) = 1.3 * 10^-11 T

    ((1.26* 10^-6)(4.61 * 10^-6))/(2*pi*0.0216) = 4.28 * 10^-11 T

    (4.28 * 10^-11) - (1.3 * 10^-11) = 2.98 * 10^-11 T

    When I checked, the answer was 22.3 pT instead of 29.8 pT.
    Can anybody please let me know what I should be doing differently?
     
  2. jcsd
  3. Oct 19, 2014 #2

    mfb

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    2017 Award

    Staff: Mentor

    I don't understand your calculations.
    This is the field 2.16cm outside, okay. The units are missing.
    What is this?
    And where is the point in subtracting the two values?

    Does the question really ask for a point outside? That would make the details about the ribbon pointless.
     
  4. Oct 19, 2014 #3
    I figured the problem out, but thank you.
     
  5. Jul 12, 2018 #4
    how did you solve it
    using what equation
     
  6. Jul 13, 2018 #5

    mfb

    User Avatar
    2017 Award

    Staff: Mentor

    This thread is from 2014 and OP didn't post anything in this forum in the last three years, it is unlikely that you will get an answer.
     
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