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Homework Help: EMF problem - Current in Coil

  1. Apr 1, 2008 #1
    [SOLVED] EMF problem - Current in Coil

    1. The problem statement, all variables and given/known data

    A small square coil is located inside an ideal solenoid at the center with its plane oriented perpendicular to the axis of the solenoid. The resistance of this coil is 2.00 [tex]\Omega[/tex] and each side is 4.00 cm long. The solenoid has 125 windings per centimeter of length. If the current in the solenoid is increasing at a constant rate of 1.50 A/s, the current in the square coil is:

    a) steady at 18.8 [tex]\mu A[/tex]
    b) initially equal at 18.8 [tex]\mu A[/tex] but is increasing
    c) increasing at 1.50 A/s
    d) decreasing at 1.50 A/s
    e) zero

    2. Relevant equations


    3. The attempt at a solution

    First, I plugged in what I know for magnetic flux:

    [tex]\Phi_{B}=BA=B(.04 m^{2})[/tex]

    Then I used that information to plug into the induced emf formula:

    And since



    [tex]\epsilon=\left|.04 m^{2}*\frac{N}{L}*\mu_{0}*\frac{di}{dt}\right|[/tex]

    [tex]\frac{di}{dt}[/tex] is 1.5 A/S
    N = (125 *.04 m) = 5


    My question is, am I going about this the right way? And if so, How do I find L and how can I use that to eventually get to the induced current?
  2. jcsd
  3. Apr 1, 2008 #2


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    Homework Helper

    Well [itex]\frac{N}{L}[/itex] is the number of turns per unit length. Which is given in the question. (Just convert the units)

    When you get the induced emf, use V=IR to find the induced current...
  4. Apr 1, 2008 #3
    Okay. (I thought L was inductance). I got a value, but how do I know if its increasing/decreasing, or steady?
    Last edited: Apr 1, 2008
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