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Force between two wires

  1. Oct 12, 2005 #1
    Hi,

    My Question:

    A rectangular loop of wire lies in the same plane as a straight wire, as show in Fig. 20-57. There is a current of 2.5A in both wires. Determine the magnitude and direction of the net force on the loop.

    http://www.webassign.net/pse/p31-09.gif

    where the width is 10.cm and width of the box is 5.0 cm and distance from the rectangular loop and the straight wire is 3.0 cm.

    My Work

    F=((mu constant)(I)^2(length))/(2pi(distance))
    F=((4pi x 10^-7 Tm/A)(2.5A)^2(.10m))/(2pi(.05m))
    F=2.5 x 10^-6 N

    but the answer in the back of the book gives F=2.6 x 10^6

    What did I do wrong:confused:

    Thank You:smile:
     
  2. jcsd
  3. Oct 12, 2005 #2

    Tom Mattson

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    Staff Emeritus
    Science Advisor
    Gold Member

    You need to calculate the force on each segment of the loop due to the long straight wire, and add them up. It looks to me like you only attempted to calculate the force on a single segment.

    It also looks like you've plugged in the wrong distance (that's supposed to be the distance from the straight wire to the segment you are analyzing).

    And this bit here is confusing:

    Which one is the "width"?
     
  4. Oct 12, 2005 #3
    Sorry,

    http://www.webassign.net/pse/p31-09.gif

    width=5 cm
    Length= 10 cm
    height= 3 cm

    I thought the width would be used for the distance, but I guess that's wrong. I tried plugging in number but with no results close to the textbook answer of 2.6 x 10^-6 N

    I still don't know what I did wrong though:confused:

    Please help and Thank You
     
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