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Transcript
Chapter 24 Capacitance, Dielectrics, Energy Storage Introduction: Our approach • Getting familiar with capacitors • Defining and calculating capacitance • Understanding what happens when capacitors are in a circuit • Understanding energy in a capacitor • Understanding the role of dielectrics in capacitors Capacitors • What are the main uses of devices called capacitors? • How does a capacitor “store charge” without having a net charge? • How are capacitors constructed? • In what sense can just about any object be considered a capacitor? Capacitance • What is the definition of capacitance? • In general, how can capacitance be calculated from the electric field? • How is capacitance calculated for a few simple capacitors? Connected Capacitors • What is meant by a (closed) electrical circuit? • How are capacitors in circuits represented diagrammatically? • What is meant by two or more capacitors in series? • What is meant by two or more capacitors in parallel? Connected Capacitors (cont’d.) • What is the equivalent capacitance for capacitors in series? • What is the equivalent capacitance for capacitors in parallel? • How is the distribution of charge determined when capacitors, some of which were initially charged, are connected in a circuit? Energy in capacitors • How is the energy in a capacitor defined? • What is the energy in a capacitor in terms of the capacitance, charge, and voltage of the capacitor? • How does the energy of a capacitor change as its separation increases? How does it matter whether the capacitor is connected to a battery? Energy in capacitors (cont’d) • Where is the energy in a capacitor? • In the above framework, how is the quantity of energy defined and expressed in terms of other quantities? Dielectrics • What is a dielectric? What are some examples? • How is the dielectric constant defined? • Why is it reasonable that a capacitor with a dielectric in the spacing has a greater capacitance? • What is dielectric strength? • What is the permittivity of a material? Dielectrics (microscopically) • What is going on microscopically when a dielectric is in a capacitor? • What is referred to by E0, Eind, σind, Qind, free charge, bound charge, K? the end