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Homework Help: Flux through loop around solenoid

  1. Apr 30, 2012 #1
    1. The problem statement, all variables and given/known data
    A simple loop of 5 cm radius encompasses the middle turns of a long coil. The coil has 2500-turns,
    is of length 1 m and radius 1 cm, and carries a current of 10 Amps. What is the magnetic flux through the single loop?

    2. Relevant equations
    B=μIN/L with L=1: B=μIN

    3. The attempt at a solution

    flux= μIN*A(loop)= 4π*10^-7*10*π*(5*10^-2)^2
    This is not right apparently

    the actual answer uses the area of the solenoid. Why is that? FLux is the B field dotted with perpendicular area, so why is it the solenoid area? That means that flux is independent of the loop's size!
  2. jcsd
  3. Apr 30, 2012 #2
    That is correct.
    Flux DENSITY = B = Webers/m^2
    Flux is in Webers = B x A.
    The solenoid is what is producing the flux and it is constant = B x Area of solenoid
  4. Apr 30, 2012 #3
    But I'm looking for the flux through the loop!
  5. Apr 30, 2012 #4


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    truesearch :smile: is right …

    there's no magnetic field (and no flux) outside the solenoid :wink:
  6. Apr 30, 2012 #5
    But the question asks if there is a magnetic flux through the loop which is outside the solenoid!
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