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Unformatted text preview: Phys102 Lecture 7/8 Capacitors Key Points Capacitors Determination of Capacitance Capacitors in Series and Parallel Electric Energy Storage Dielectrics References SFU Ed: 241,2,3,4,5,6. 6 th Ed: 177,8,9,10+. A capacitor consists of two conductors that are close but not touching. A capacitor has the ability to store electric charge. Parallelplate capacitor connected to battery. (b) is a circuit diagram. When a capacitor is connected to a battery, the charge on its plates is proportional to the voltage: The quantity C is called the capacitance. Unit of capacitance: the farad ( F ): 1 F = 1 C/V. 241 Capacitors Determination of Capacitance For a parallelplate capacitor as shown, the field between the plates is E = Q / A. The potential difference: V ba = Ed = Qd / A. This gives the capacitance: Example 241: Capacitor calculations. (a) Calculate the capacitance of a parallelplate capacitor whose plates are 20 cm 3.0 cm and are separated by a 1.0mm air gap. (b) What is the charge on each plate if a 12V battery is connected across the two plates? (c) What is the electric field between the plates? (d) Estimate the area of the plates needed to achieve a capacitance of 1 F, given the same air gap d . Capacitors are now made with capacitances of 1 farad or more, but they are not parallel plate capacitors. Instead, they are activated carbon, which acts as a capacitor on a very small scale. The capacitance of 0.1 g of small scale....
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This note was uploaded on 10/14/2010 for the course PHYS PHYS 102 taught by Professor Michaelchen during the Fall '10 term at Simon Fraser.
 Fall '10
 MichaelChen
 Capacitance, Energy

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