Gausslaw q da eg 0 q da eg 1q 4 r 2 0 enclosed

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Unformatted text preview: 4) Q enclosed =0 +Q must be on inside surface (a3), so that Qenclosed = + Q – Q = 0 Calculation Calculation cross-section +Q A capacitor is constructed from two conducting cylindrical BB shells of radii a1, a2, a3, and a4 and length L (L >> ai). + + − − − + + + −−− − − + + What is the capacitance C of this capacitor ? − ­Q − − + + − − + + − − metal − − − + + +++ + + a2 a1 + a4 a3 C≡ Q V metal Where is ­Q on inner conductor located? (A) at r=a2 (B) at r=a1 (C) both surfaces (D) throughout shell Why? Gauss’ law: Q dA ∫ Eg = ε enclosed Q 0 enclosed =0 We know that E = 0 in conductor (between a1 and a2) Q enclosed =0 ­Q must be on outside surface (a2), so that Qenclosed = 0 Calculation Calculation cross-section +Q A capacitor is constructed from two conducting cylindrical shells BB of radii a1, a2, a3, and a4 and length L (L >> ai). + + − − − + + + −−− − − + + What is the capacitance C of this capacitor ? − ­Q − − + + − − + + − − metal − − − + + +++ + + a2 a1 + a4 a3 C≡ metal Q V a2 < r < a3: What is E(r)? 1Q 1 2Q 1Q (A) 0 (B) (C) (D) (E) 2πε Lr 2πε Lr 4πε r 2 0 0 Why? Gauss’ law: Q dA ∫ Eg = ε 0 Q dA...
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