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Homework Help: Amplitude of the induced voltage across the coil

  1. Mar 30, 2010 #1
    If anyone can advise that would be great.

    1. The plane of a 5 turn coil of 5mm² cross sectional area is rotating a 1200 r.p.m in a magnetic field of 10mT.

    Q. Calculate the amplitude of the induced voltage across the coil


    5 turns
    c = 1200 rpm
    A = 5cm²
    B = 10 mT

    2. φ = N.B.A φ = 5×10×10^-3 ×5 × 10^-2
    φ = 2.5 ×10^-3

    V = dφ/dt or N.A. dB/dt

    The equation thought to have been used is the following but the Length is not vissible to me.

    V/L = c x B c being the speed
    B field
    L lenth of wire

    3. I have tried two avenues please advise

    a: V(t) = -N•d(B•A)/dt = -N•B•dA/dt = N•B•ω•A•sin(ωt)
    V(t) =(5)(10x10^-3)(125.66370599999999)(5)sin(ωt) = 31.415 sin(ωt) volts.


    b: And using the following, saying t = 60 sec

    Then φ = N.B.A φ = 5×10×10^-3 ×5 × 10^-2
    φ = 2.5 ×10^-3

    And V = dφ/dt or N.A. dB/dt = 4.17x10^-3 V

    My concern here is that 1200rpm was not used.
    Last edited: Mar 30, 2010
  2. jcsd
  3. Apr 2, 2010 #2


    User Avatar

    Staff: Mentor

    You should write out the function φ(t) (hint: it is a sinusoidal function), then differentiate it to find V(t)...
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