Unformatted text preview: A uniform electric field is confined to a circular region of radius, r , and is increasing with time. What is the direction and magnitude of the induced magnetic field at the radius r? Answer: If I choose my orientation to be counterclockwise then Φ E = E(t)A with A = π r 2 . Ampere’s Law ( with J = 0 ) tells us that r r B dl rB r d dt r c dE dt E Circle ⋅ = = = ∫ 2 2 2 πε µ π ( ) Φ , and hence B(r) = (r/2c 2 ) dE/dt . Since dE/dt > 0 ( increasing with time ), B is positive which means that it points in the direction of my chosen orientation. Bout increasing with time r E Eout increasing with time r B...
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 Spring '08
 FRY
 Physics, Magnetic Field, R. D. Field

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