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Magnetic flux through a solenoid

  1. Mar 30, 2010 #1
    ok, the magnetic field through a single ring is n[tex]\mu[/tex]I ,
    so the flux is BAcos(theta), with cos(theta)=1, flux = BA = piR2n[tex]\mu[/tex]I

    so why for the entire solenoid flux, it is now nL*the flux above? where L = length of solenoid

    shouldn't multiplying it with just n = number of rings be suffice?

    also, i don't really understand the magnetic flux. is it define to be the number of field lines per unit area? it is something like density right? so shouldn't it be flux = B/A ? i am getting confused :X

  2. jcsd
  3. Mar 30, 2010 #2
    Those formulas look pretty wrong. The flux should decrease with the length of the coil. And your first formula contains a number n that is not even defined for a single loop (or simply n=1)

    Maybe this helps: http://en.wikipedia.org/wiki/Solenoid
  4. Mar 31, 2010 #3
    yup, for a single coil , n = 1.

    but i don't understand why for the entire solenoid, we use n*L*dflux/dt = induced EMF

    shouldn't just multiplying with n be enough? because n = number of turns. and dflux/dt is for 1 turn. so the entire solenoid just needs to be multiplied by n turns. why do we multiply another length L factor? it is taken from masterphysics.com
  5. Mar 31, 2010 #4
  6. Mar 31, 2010 #5
    oh i realise where it all went wrong. after reading the question again for the 3000 time, i realise that n was the number of turns per unit length. so to get N, number of turns, we have to multiply n with L. -.-

    sorry for the commotion
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