**Unformatted text preview: **J is constant however inside the area of a thin ring: dr r dA 2 π = (For a derivation of this, look in your calculus books for the infinitesimal area d A = (d r )( r d φ ) in the case of polar coordinates.) Putting things together we find, using R = 0.002 m, A 10 5 . 2 2 2 ) 2 ( 3 × = = = = ∫ ∫ BR dr B dr r r B i R R...

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