# lec05 - • The capacitance of a capacitor increases by a...

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Capacitor and Capacitance A capacitor is a device which stores charge. It consists of two conductors (of any shape) placed near each other. A battery is used to charge a capacitor. The battery in effect removes charge from one conductor and deposits it on the other. When charged, each conductor carries a charge of the same magnitude, but opposite in sign. The magnitude of the charge q on each conductor is directly proportional to the potential difference V between the conductors: Therefore where C is the capacitance. The unit of C is Farad (=Coul/Volt) In general , the value of capacitance C depends on geometric construction of the capacitor. For a parallel plate capacitor of area A and plate spacing d V q CV q = d A C 0 ε = ) / 10 85 . 8 4 1 ( 2 2 12 0 Nm C k × = = π A (area) d + Battery +q -q V + + + + +

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Capacitors and Dielectric
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Unformatted text preview: • The capacitance of a capacitor increases by a factor κ when a piece of insulating ( dielectric ) material is inserted between the plates. – Where C is the capacitance before the dielectric is inserted, and is the dielectric constant of the material – This increase is due to induced surface charge on the dielectric. • For a parallel plate capacitor with dielectric: • Energy is stored in a capacitor when charged. – The stored energy is equal to the amount of work done by the battery in transfer charge from one plate to the other. – For a capacitor with charge magnitude q and potential difference V between the plates C C = d A C κε = d A (area) dielectric C q CV qV Energy 2 2 1 2 1 2 2 = = =...
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lec05 - • The capacitance of a capacitor increases by a...

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