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Homework Help: Current in Two Loops

  1. Mar 9, 2015 #1
    1. The problem statement, all variables and given/known data

    Except for the loops -- and the fact that current runs through them in opposite directions -- DISREGARD THIS DIAGRAM

    Two wire loops have current travelling in opposite directions. My problem asks me to determine whether a force exists between both loops and, if so, then in which direction (attractive or repulsive). The correct answers are "yes" and "repulsive."

    I want to understand why my logic isn't sound:

    2. Relevant equations
    Right hand rules

    3. The attempt at a solution

    1) Induced magnetic fields oppose each other
    2) To evaluate the force applied on one loop, we need to:
    a) Determine the direction of the magnetic field in the other loop
    b) Apply the right-hand rules on one particle of the loop in question
    3) The field running through the right hand loop points leftwards
    a) a particle going around the loop experiences a radially outward force
    b) all particles also experience radially outward forces
    c) net force should cancel
  2. jcsd
  3. Mar 11, 2015 #2


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    Staff: Mentor

    Why radial outwards? The field is "circular" around the wire of loop 1, so it points in radial direction at the point where loop 2 is.
  4. Mar 11, 2015 #3
    what do you meanby "circular" around the wire of loop 1? I take your description to mean:

    1) Loop 1 creates a magnetic field
    2) part of that magnetic field runs THROUGH loop 2
    3) part of that magnetic field also runs around loop 2 on either side
  5. Mar 11, 2015 #4


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    Staff: Mentor

    Circular as in this image. If you imagine another wire nearby, running in the same direction, the wires attract or repel (based on the current direction).
  6. Mar 12, 2015 #5

    rude man

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    You can also look at this as two magnets formed by the two loops. Since the currents oppose you will get two N or two S poles facing each other.
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