1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Find the maximum induced emf in the large coil solenoid

  1. Jul 30, 2007 #1
    1. The problem statement, all variables and given/known data
    Given: u_0 = 1.25664e-6
    A 2 m long large coil with a radius of 14.6 cm and 320 turns surrounds a 4.2 m long solenoid with a radius of 4.6 cm and 7700 turns. The current in the solenoid changes as I = I_0 sin (2pi*f*t) where I_0= 30 A and f=60 Hz.Inside solenoid has 7700turns and outside coil has 320 turns. The equation for the emf is E = E_0sin(omega*t). There is also a resistor on the smaller coil that is 25 ohms. Find the maximum induced emf in the large coil. Answer in units of V.

    2. Relevant equations
    Magnetic field = B = u_0 * I / (2*pi*r)
    Flux = BA

    3. The attempt at a solution
    I found the magnetic field of the solenoid (0.069115sin(120*pi*t)) and the area (0.006648). I then multipled BA to find the flux which is (0.000459 sin(120*pi*t))

    Then I found the magnetic field of the outer coil ((0.006032sin(120*pi*t)) and the area to be 0.066966.
    The magnetic flux is BA = (0.000404sin(120*pi*t))

    Now I am truly stuck because I've no clue where to go from here. Please help! Many thanks.
  2. jcsd
  3. Jul 31, 2007 #2
    I think Ohm's Law and Faraday's Law would help:

    [tex]\displaystyle V = iR[/tex]

    [tex]\displaystyle \oint\vec{E}\cdot d\vec{l} = \mathcal{E}_{ind} = -\frac{d\Phi_B}{dt}[/tex]
  4. Jul 31, 2007 #3
    Hmm...I'm still lost. Could you perhaps clarify what you mean and how those two equations would relate to each other.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook