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Kruum
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Homework Statement
http://www.aijaa.com/img/b/00106/3735947.jpg
Homework Equations
[tex] \epsilon =- \frac {d \Phi}{dt}=- \frac {d BA}{dt}= \oint \vec{E} \cdot d \vec{l} [/tex]
[tex] B= \mu _0nIA [/tex], where n is solenoid's turns per meter.
The Attempt at a Solution
I was able to solve this through trial and error, almost. What I got is [tex] \epsilon =- \frac { \mu _0 nAdI}{dt} \Longrightarrow \frac {dI}{dt}=- \frac {E2 \pi r_1}{ \mu _0n \pi r_{2}^2}=-9.21 \frac{A}{s}[/tex], where r1=0.035m and r2=0.011m. Our assistant teacher wasn't able to tell me why we to take the line integral over a circle in [tex] \epsilon = \oint \vec{E} \cdot d \vec{l} [/tex] and why my sign is wrong. Can somebody help?
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