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Homework Help: 10 cm diameter loop in magnetic field

  1. Mar 13, 2017 #1
    1. The problem statement, all variables and given/known data

    The figure shows a 10-cm diameter loop in three different magnetic fields. The loop's resistance is 0.10 Ω. For each case, determine the induced emf, the induced current, and the direction of the current.


    2. Relevant equations

    Faraday's Law: εinduced= - (ΔΦb/Δt) = - A ⋅ ΔB / Δt
    Lenz's Law

    3. The attempt at a solution

    εinduced= - (ΔΦb/Δt)
    εinduced= -0.50 T/sec ⋅ π ⋅ 0.052m2
    εinduced= -3.93 × 10-3 V

    For part A: The flux is increasing, and the external magnetic field is going upward through the loop, so shouldn't the induced magnetic field go in opposite direction (downward) to oppose the external magnetic field? And so therefore shouldn't the induced current be clockwise around the loop according to the right hand rule?

    the flux is decreasing and the magnetic field is going into the loop (into the page). So since the flux through the loop is decreasing wouldn't this say that the the induced magnetic field goes in same direction of external magnetic field to try and prevent the decrease; and thus the current goes counter-clockwise?

    c) The field does not penetrate the loop so the emf and current are 0.
    Last edited: Mar 13, 2017
  2. jcsd
  3. Mar 14, 2017 #2
    Your reasoning and answers are good, except check your right hand rule for b again.
  4. Mar 14, 2017 #3


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    Don't forget to calculate the value of current in each case.
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