lecture05

# lecture05 - 6 Capacitance and capacitors 6.1 Capacitors...

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Unformatted text preview: 6. Capacitance and capacitors 6.1 Capacitors +Q-Q-Q +Q-Q +Q 6.2 Capacitance [C]= 1 F = 1 C / V V Q C = Definition: Units: Symbol : - +- â‰¡ âˆ† â‰¡ V V V V C is independent from: Q and Î” V (Î” V is always proportional to Q ) C depends on: â€¢ the geometry of the system â€¢ the dielectric between the conductors 6.3 Parallel plate capacitor-Q +Q d E A Q E Îµ Îµ Ïƒ = = A Qd Ed V V V a b Îµ = =- â‰¡ a b V Q C = d A C Îµ = 6.3a Cylindrical capacitor: = a b L C ln / 2 Ï€Îµ 6.3b Spherical capacitor: b a a C / 1 4- = Ï€Îµ Large plates of area A separated by a small distance d, can be considered as infinite planes. Example (Variable capacitor): A parallel plate capacitor is connected to a battery that produces a constant potential difference across its plates. If we push the plates of the capacitor together so that the distance between them is halved, the charge on the capacitor changes by: battery- + C d â†’ d/ 2 V - const Q = CV A C d Îµ = C â†’ 2 C Q â†’ 2 Q A. Â½A....
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## This note was uploaded on 11/17/2011 for the course PHYS 5863005 taught by Professor Meyer during the Fall '09 term at Iowa State.

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lecture05 - 6 Capacitance and capacitors 6.1 Capacitors...

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