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Direction of the induced current and polarity

  1. Apr 17, 2013 #1
    1. The problem statement, all variables and given/known data
    http://img805.imageshack.us/img805/6030/82154948.png [Broken]
    Find Vemf (between points 1 and 2) and it's polarity at t = 0.
    I have omitted details because my question is specifically on the polarity.


    2. Relevant equations
    Lenz's law:
    An induced electromotive force (emf) always gives rise to a current whose magnetic field opposes the original change in magnetic flux.

    Vemf = -dΦ/dt

    3. The attempt at a solution
    This is a worked out example in my textbook. We first find the flux Φ and Vemf which are function of time. We compute dΦ/dt at t = 0. Then Vemf = -dΦ/dt.

    We find that dΦ/dt > 0, so the magnetic field B is increasing. To counter-act this change, I must be in the direction given in the picture. Everything is ok at this point.

    Now here is where I get lost. My textbook says:

    I thought I always is from the higher potential to the lower potential. Which should make terminal 1 at a higher potential than terminal 2 considering the direction of I. It seems like the textbook have it reversed.

    What am I missing?
     
    Last edited by a moderator: May 6, 2017
  2. jcsd
  3. Apr 17, 2013 #2
    Is it a matter of conventional current vs electrons flow?
     
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