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https://s1.lite.msu.edu/enc/53/3b1b...bbf37ae59602796c87a446f0a53c5801a82918f44.gif

The variable resistor is changed so that the solenoid current decreases linearly from 6.81 A to 1.59 A in 0.225 s. Calculate the induced emf in the circular loop. (The field just outside the solenoid is small enough to be negligible.)

phi(flux)= ∫B*dA

ε= dphi/dt

A(circle)=∏r^2

B= N*mu_0_*I/L (solenoid)

I'm having troubles finding the flux through the loop. I tried taking the integral from .0410 to .197 m but I don't think that is right. I know once I get my flux integral i can take the flux at both currents, find the difference between the two, and divide by .225 s to find the induced emf. I just don't know what to integrate over.