capacitance - (www.ramsey.k12.nj.us).
advertisement
LECTURE_CAPACITANCE September 25, 2014 CAPACITANCE 1 LECTURE_CAPACITANCE September 25, 2014 TABLE of CONTENTS CAPACITORS/CAPACITANCE Physical Characteristics of a Capacitor Storage of Electric Energy CAPACITORS IN ELECTRICAL CIRCUITS Summary 2 LECTURE_CAPACITANCE September 25, 2014 We have learned about practical applications of conductors in electric fields, such as grounding and shielding. Another important application involving electric fields and conductors is storing energy in the form of electric potential energy. When positively and negatively charged objects are separated, the system's electric potential energy increases. How can this charge separation be maintained so that the electric potential energy can be stored for useful purposes? This is accomplished with a device known as a capacitor. 3 LECTURE_CAPACITANCE September 25, 2014 Charging a Capacitor A capacitor In the process of charging A capacitor consists of two conducting surfaces separated by a nonconducting material. 4 LECTURE_CAPACITANCE Capacitor is now fully charged September 25, 2014 The E fields produced on each plate 5 LECTURE_CAPACITANCE The E fields produced on each plate September 25, 2014 The E fields for both plates when together The net E field The net E field is strong between the plates and zero outside 6 LECTURE_CAPACITANCE September 25, 2014 For a uniform Electric Field ∆V = ­E∆d Double V means double E caused by double Q Q = CV C is proptionality constant, called the capacitance, in Farads. 1F = 1C/1V 7 LECTURE_CAPACITANCE September 25, 2014 What properties of capacitors determine their capacitance? The capacitor with the larger surface Now imagine two capacitors area A plates should be able to with the same surface area and maintain more charge separation the same potential difference because there is more room for the across the plates but with charge to spread out different distances d between the plates. But since the magnitude of this E field is proportional to the amount ofelectric charge on the plates, a larger plate separation leads to a smaller magnitude of electric charge on the plates (+q on one and —q on the other). This means the capacitance of the capacitor decreases with increasing d. 8 LECTURE_CAPACITANCE September 25, 2014 9 LECTURE_CAPACITANCE September 25, 2014 A capacitor consists of two conductors that are close but not touching. A capacitor has the ability to store electric charge. 10 LECTURE_CAPACITANCE September 25, 2014 R. W. E. Capacitors 11 LECTURE_CAPACITANCE September 25, 2014 Heart defibrillators use electric discharge to “jump­start” the heart when its beats become irregular, and can save lives. 12 LECTURE_CAPACITANCE September 25, 2014 Parallel­plate capacitor connected to battery. 13 LECTURE_CAPACITANCE September 25, 2014 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. The unit of capacitance is the farad (F) 1 F = 1 C/V 14 LECTURE_CAPACITANCE September 25, 2014 Physical Characteristics of a Capacitor The capacitance does not depend on the voltage; it is a function of the geometry and materials of the capacitor. For a parallel­plate capacitor: 15 LECTURE_CAPACITANCE September 25, 2014 16 LECTURE_CAPACITANCE September 25, 2014 17 LECTURE_CAPACITANCE September 25, 2014 18 LECTURE_CAPACITANCE September 25, 2014 19 LECTURE_CAPACITANCE September 25, 2014 20 LECTURE_CAPACITANCE September 25, 2014 21 LECTURE_CAPACITANCE September 25, 2014 22 LECTURE_CAPACITANCE September 25, 2014 23 LECTURE_CAPACITANCE September 25, 2014 24 LECTURE_CAPACITANCE September 25, 2014 25 LECTURE_CAPACITANCE September 25, 2014 26 LECTURE_CAPACITANCE September 25, 2014 27 LECTURE_CAPACITANCE September 25, 2014 Q = CV 28 LECTURE_CAPACITANCE September 25, 2014 Storage of Electric Energy A charged capacitor stores electric energy; the energy stored is equal to the work done to charge the capacitor. Using Q = CV 29 LECTURE_CAPACITANCE September 25, 2014 I. E. Capacitance I.E. Capacitance 30 LECTURE_CAPACITANCE September 25, 2014 CAPACITORS in ELECTRICAL CIRCUITS CAPS in PARALLEL QT = CTV 31 LECTURE_CAPACITANCE September 25, 2014 CAPS in SERIES 32 LECTURE_CAPACITANCE September 25, 2014 33 LECTURE_CAPACITANCE September 25, 2014 34 LECTURE_CAPACITANCE September 25, 2014 35 LECTURE_CAPACITANCE September 25, 2014 36 LECTURE_CAPACITANCE September 25, 2014 Summary Capacitor: nontouching conductors carrying equal and opposite charge Capacitance: Capacitance of a parallel­plate capacitor: 37 LECTURE_CAPACITANCE September 25, 2014 38
