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Homework Help: Electric Field of a Solenoid

  1. Jul 31, 2013 #1
    1. The problem statement, all variables and given/known data

    A long solenoid of radius R, length L (which
    is much longer than R), number of windings
    N, has a current I that is changing in time at
    a rate (dI/dt). What is the magnitude of the
    electric eld a distance R=2 from the axis of
    the solenoid?

    2. Relevant equations


    3. The attempt at a solution

    I thought I had this completely right until I get to the R/2 Part. if you just throw the R/2 part into the equation, then you get the B field I believe, but the answer is: μ0(dI/dt)(N/L)R/4.

    I am not seeing where the 4 in the denominator comes from unless we had some kind of divisible action of R going on somewhere, or something. Not really sure how to proceed!
  2. jcsd
  3. Aug 1, 2013 #2

    rude man

    User Avatar
    Homework Helper
    Gold Member

    Start by stating the problem correctly. What do you mean by "R=2"? Did you mean R/2? 2R?
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