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: Energy Dissipated in Loop (Magnetic Field)-

  1. Apr 2, 2012 #1
    Energy Dissipated in Loop (Magnetic Field)-- Please Help!

    1. The problem statement, all variables and given/known data

    What is the energy dissipated as a function of time in a circular loop of N turns of wire having a radius of r and a resistance of R if the plane of the loop is perpendicular to a magnetic field given by

    2. Relevant equations


    3. The attempt at a solution

    I first wanted to calculate the EMF, and since the B field varies, I found the derivative of the B field, times the number of turns times the area:
    Then squaring this term and multiplying it by 1/R will equal the time-derivative of the energy dissipated
    dE/dt = (NA)^2*(t/tau)^2*(B^2)e^(-2t/tau)

    Bringing dt over and integrating from 0 to t I find (and substituting pi*r^2 for A):
    E=(N*pi*r^2)^2*(B^2)(tau^2-e^(-2t/tau))(2t^2+2t*tau + tau^2)/(4R*tau)

    This is not the correct answer, though.

    Any help??? Please!
  2. jcsd
  3. Apr 2, 2012 #2


    User Avatar

    Staff: Mentor

    Re: Energy Dissipated in Loop (Magnetic Field)-- Please Help!

    Your derivative of the B field doesn't look right. Since you're taking the derivative w.r.t. time the t shouldn't be coming down from the exponent.
  4. Apr 2, 2012 #3
    Re: Energy Dissipated in Loop (Magnetic Field)-- Please Help!

    Oh-duh! Thank you--got it now.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook