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 E 0, E ind, σ ind, Q ind, free charge, bound charge, K?

the end