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A coil moves into a magnetic field

  1. Dec 16, 2015 #1
    1. The problem statement, all variables and given/known data
    A coil, made up of 1850 loops, is inserted in an electric circuit and has a resistance of 45,0Ω. The area of each loop is 4,70⋅10^(-4) m^(2). The coil moves from a region where there's no magnetic field, to a region where the magnetic field is present. The normal to the coil stays parallel to the magnetic field. The induced charge that flows into the circuit is 8,87⋅10^(-3) C. Find the intensity of the magnetic field.

    Number of loops: 1850
    Resistance: 45,0Ω
    Area of a loop: 4,70⋅10^(-4) m^(2)
    Induced charge: 8,87⋅10^(-3) C

    2. Relevant equations

    magnetic field in the centre of a coil B= N⋅μ⋅i / (2⋅R)
    Faraday-Neumann law ΔV = - Δφ/ Δt

    3. The attempt at a solution
    I thought about finding the intensity of the magnetic field by using the Faraday-Neumann law, since the flux of a magnetic field is equal to φ= B⋅A, and the problem gives us the area of a loop. Then, in fact, I would try to find ΔV and Δt so that I could get B, but I don't know how to proceed to find neither of them. I thought about using the first Ohm law to find ΔV, since the problem gives us the resistance of the coil, but it doesn't give us the current. Do you have any suggestions? Thank you!
  2. jcsd
  3. Dec 16, 2015 #2


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    Hello. Welcome to PF!

    You are on the right track with Faraday's law and Ohm's law. (The formula for the field at the center of a coil is not relevant here.) Can you write out Faraday's law explicitly in terms of the number of turns, the field, the area, and the time interval?

    As a suggestion, you might think about the relation between the current and the total charge that flows.
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