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Find the induced EMF and Lenz' law

  1. Mar 27, 2016 #1
    1. The problem statement, all variables and given/known data
    There is a magnetic feild directed inside/ towards the screen. There is also a single rectangular coil parallel to the screen where one of the sides are movable. The magnetc feild increases, what happens to this movable side of the coil. This is my description of the problem, the original was displayed diagrammatically so please ask me to clarify if needed.

    2. Relevant equations
    Lenz's law

    3. The attempt at a solution

    The induced emf in the coil would be anti-clockwise. In order to oppose this change an emf will be induced in the coil. I dont know why the side of the coil should move at all but the answer is that it moves to the right. Can anyone explain to me why?
     
  2. jcsd
  3. Mar 27, 2016 #2

    berkeman

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    Staff: Mentor

    Can you write out Lenz' Law for us? And are you familiar with Ampere's Law? And have you learned about the Lorentz Force yet?
     
  4. Mar 27, 2016 #3
    Didn't learn about Lorentz Force but I do know ampere's law.
    So Lenz's law- The induced current will be in a direction to oppose the change in magnetic flux that created the current. In this case -
    Φ=BA
    Φ(flux),(B) magnetic field strength and A (area of loop)
    So it occurred to me now that oposing a change in flux is like keeping Φ constant. If B is increasing then it makes sense that A would have to decrease to keep it constant. This agrees with the answer as moving the side of the coil to the right would decrease the area(would make better sense with the diagram).
    So is this like an alternative to producing an emf?I mean just by reducing the area a change in flux was avoided so a current wont be induced in the coil. Im guessing this is what actually happens but why reduce area over inducing current?
     
  5. Mar 28, 2016 #4

    berkeman

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    Staff: Mentor

    I don't know if that's a correct interpretation. It may be, but it's not the explanation I'm familiar with.

    Changing the flux through the loop will induce a current in the loop. The moving charges in the wire sections experience the Lorentz Force F = qv X B which is normal to both the charges' velocity vector v and the B field vector. That is where the force comes from to move the wire. You just have to use Ampere's Law and the Righthand Rule to figure out which way the wire moves.
     
  6. Mar 28, 2016 #5
    Yes! This makes so much more sense, it works. Thank you
     
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