chapter26_1class

chapter26_1class - Charges positive (+) negative (-)...

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Unformatted text preview: Charges positive (+) negative (-) conservation Force (field) Potential (energy) 12 12 12 r r F 2 2 2 2 1 2 2 1 4 1 r q q r q q k e = = Force between point charges e q = F E Force on charge in the field A E q d E = = Connect field with its source: charge =- B A d V s E qV U = Connect field with energy What for? To understand the world Or to move on to capacitor, one of the three passive components in circuits Chapter 26 Capacitance and Dielectrics Capacitors = that which have capacitance to hold = containers Capacitors are devices that store electric charge Any conductors can store electric charge, but Capacitors that specially designed devices to story a lot of charges Examples of where capacitors are used include: radio receivers filters in power supplies to eliminate sparking in automobile ignition systems energy-storing devices in electronic flashes How is my English? Capacitance The capacitance , C , is defined as the ratio of the amount of the charge Q on the conductor to the potential increase V of the conductor because of the charge: This ratio is an indicator of the capability that the object can hold charges. It is a constant once the object is given, regardless there is charge on the object or not. This is like the capacitance of a mug which does not depend on there is water in it or not. The SI unit of capacitance is the farad (F) V Q C Q V C= 1V 1C F 1 = More About Capacitance Capacitance will always be a positive quantity The capacitance of a given capacitor is constant The capacitance is a measure of the capacitors ability to store charge The farad is an extremely large unit, typically you will see microfarads ( F=10-6 F), nanofarads (nF=10-19 F), and picofarads (pF=10-12 F) Capacitance of a one conductor system is small: for example, Isolated Sphere...
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This note was uploaded on 05/06/2008 for the course PHYS 1304 taught by Professor Ye during the Spring '08 term at SMU.

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chapter26_1class - Charges positive (+) negative (-)...

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