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chapter26_1class

# chapter26_1class - Charges positive negative conservation...

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Charges positive (+) negative (-) conservation Force (field) Potential (energy) 12 12 12 r r F ) ) r 2 2 1 0 2 2 1 4 1 r q q r q q k e πε = = Force between point charges e q = F E r r Force on charge in the field 0 A E ε Φ q d E = = r r Connect field with its source: charge = - B A d V s E r r Δ 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

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Chapter 26 Capacitance and Dielectrics
Capacitors = that which have capacitance to hold = containers circle6 Capacitors are devices that store electric charge circle6 Any conductors can store electric charge, but circle6 Capacitors that specially designed devices to story a lot of charges circle6 Examples of where capacitors are used include: circle6 radio receivers circle6 filters in power supplies circle6 to eliminate sparking in automobile ignition systems circle6 energy-storing devices in electronic flashes How is my English?

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Capacitance circle6 The capacitance , C , is defined as the ratio of the amount of the charge Q on the conductor to the potential increase Δ V of the conductor because of the charge: circle6 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. circle6 The SI unit of capacitance is the farad (F) V Q C Δ Q V C= 1V 1C F 1 =
More About Capacitance circle6 Capacitance will always be a positive quantity circle6 The capacitance of a given capacitor is constant circle6 The capacitance is a measure of the capacitor’s ability to store charge circle6 The farad is an extremely large unit, typically you will see microfarads ( μ F=10 -6 F), nanofarads (nF=10 -19 F), and picofarads (pF=10 -12 F)

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Capacitance of a one conductor system is small: for example, Isolated Sphere circle6 Assume a spherical charged conductor with radius R circle6
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chapter26_1class - Charges positive negative conservation...

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