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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

B(t)=B_{0}e^{-t/tau}

2. Relevant equations

P=I^2*R=EMF^2/R

EMF=-d/dt(flux)=-dB/dt*NA

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:

EMF=NA*(t/tau)Be^(-t/tau)

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!

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# Homework Help: Energy Dissipated in Loop (Magnetic Field)-

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