Unformatted text preview: then Φ B = BA and ε = -d Φ B /dt = -A dB/dt = -( π r 2 )(-20T/s) = 62.8 V . The induced current is I = ε /R = (62.8 V)/(5 Ω ) = 12.6 A . Since ε is positive the current is flowing in the direction of my chosen orientation ( counterclockwise ). The induced magnetic field at the center of the circle is given by B ind = 2 π kI/r = (2 π x 10-7 Tm/A)(12.6 A)/(1 m) = 7.9 µ T and points out of the paper . Lenz’s Law: It is a physical fact not a law or not a consequence of sign conventions that an electromagnetic system tends to resist change. Traditionally this is referred to as Lenz’s Law: Induced EMF’s are always in such a direction as to oppose the change that generated them. B-out changing with time r Loop...
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- Spring '08
- Physics, Magnetic Field, Lenz