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Homework Help: Magnetic Fields

  1. Dec 2, 2007 #1
    1. Magnetic field inside a long solenoid with cross-sectional area A is given by B=(mu)nI where n is the number of turns per unit length and I is the current. Suppose that the current is given by I(t) = I(0)e^(a*t) where t is the time and a and I(0) are constants. What is the magnetic flux through the solenoid as a function of t? Hence find the induced emf outside the solenoid as a function of time

    2. Relevant equations
    Magnetic flux is the integral of B.dA
    Faraday's Law: Emf = rate of change of magnetic flux through loop

    Not quite sure how to start. Could someone please help!!
  2. jcsd
  3. Dec 3, 2007 #2


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    For a long solenoid, what is the direction of the B-field inside the solenoid? And is B a function of the position inside? What does this make [itex]\int B\cdot dA~=~[/itex] ?
  4. Dec 5, 2007 #3
    Inside the solenoid the magnetic field B will be horizontal. But we know from the equation B=mu*n*I that it doesn't depend on the radius of the solenoid.
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