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Anyone see where I messed up on finding the current?

  1. Nov 12, 2005 #1
    I'm not sure what i'm doing wrong...
    Two long straight wires are parallel and 5.0 cm apart. They are to carry equal currents such that the magnetic field at a point halfway between them has magnitude 320 µT.

    (a) Should the currents be in the same or opposite directions?
    same
    opposite
    correct check mark
    (b) How much current is needed?
    wrong check mark A

    Here is my work:
    http://show.imagehosting.us/show/916283/0/nouser_916/T0_-1_916283.jpg

    Thanks!
     
  2. jcsd
  3. Nov 12, 2005 #2

    Chi Meson

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    check "r." What is this distance supposed to be?
     
  4. Nov 13, 2005 #3
    Consider that one wire should be producing HALF of the field...
    I Agree with Chi... Check your r value.
     
  5. Nov 13, 2005 #4
    I did what i think u guys ment....since its only half way, I took half the distance .05m, which is .025, and i plugged it into the formula:
    (B*2PI*r)/u = i;
    i = (320E-6)(2*PI*(.025)/1.26E-6
    i = 39.89 which was also wrong
    is that what u guys ment?
     
  6. Nov 13, 2005 #5

    lightgrav

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    don't you have two wires? Both contribute the the B-Field.
     
  7. Nov 13, 2005 #6
    So is the mangintude of the b field just multiplied by 2? or would it be 0? because they are producing a repulisve force on eachother, and the currents are equal
     
  8. Nov 13, 2005 #7

    Chi Meson

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    Part of the question is to decide which way the currents must run, parallel or antiparallel. One way will cancel the fields, the other way will add up the fields. Use the right hand.
     
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