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Homework Help: Magnitude of the non-coulomb electric field around a solenoid.

  1. Nov 10, 2012 #1
    1. The problem statement, all variables and given/known data

    A metal ring of radius r = 24 cm surrounds a
    solenoid of radius R = 2 cm and 10000 turns.
    The magnetic field inside the solenoid changes from 5 T to 3 T in
    0.1 s. Find the magnitude of the non-Coulomb
    electric field along the ring.
    Answer in units of V/m

    2. Relevant equations

    emf = -N*d(flux)/dt = -N*db/dt*A
    emf = integral of E*dl

    3. The attempt at a solution

    Ok, so i pretty much just plugged in numbers. for the emf:

    emf = -10000*(3-5)/0.1*pi*0.02^2 = 251.3 volts.

    For the electric field:

    E = emf/L = 251.3/2*pi*0.24 = 166.7 V/m

    Unfortunately, the computer keeps saying i'm wrong. Am I really doing something wrong? This seemed pretty straight forward.
  2. jcsd
  3. Nov 10, 2012 #2
    You're looking at the emf induced in the metal ring. How many turns of wire does a metal ring have?
  4. Nov 11, 2012 #3
    Wait, so you have to use the emf equation from the ring's perspective?

    emf = (3-5)/0.1*pi*0.24^2 = 3.62 volts.

    E = emf/L = 251.3/2*pi*0.24 = 2.40 V/m

    Or do I still use the solenoid's area for the emf?
    Last edited: Nov 11, 2012
  5. Nov 11, 2012 #4
    I have until 11:30 ct to finish this one problem, can anyone please give input.
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