Fisica

Chapter 26

Capacitance and Dielectrics
CHAPTE R OUTLI N E

26.1 Definition of Capacitance 26.2 Calculating Capacitance 26.3 Combinations of Capacitors 26.4 Energy Stored in a Charged Capacitor 26.5 Capacitors with Dielectrics 26.6 Electric Dipole in an Electric Field 26.7 An Atomic Description of Dielectrics

L All of these devices are capacitors, which store electric charge and energy. A capacitor is one type of circuit element that we can combine with others to make electric circuits. (Paul Silverman/Fundamental Photographs)

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In this chapter, we will introduce the first of three simple circuit elements that can be

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connected with wires to form an electric circuit. Electric circuits are the basis for the vast majority of the devices that we use in current society. We shall discuss capacitors— devices that store electric charge. This discussion will be followed by the study of resistors in Chapter 27 and inductors in Chapter 32. In later chapters, we will study more sophisticated circuit elements such as diodes and transistors. Capacitors are commonly used in a variety of electric circuits. For instance, they are used to tune the frequency of radio receivers, as filters in power supplies, to eliminate sparking in automobile ignition systems, and as energy-storing devices in electronic flash units. A capacitor consists of two conductors separated by an insulator. The capacitance of a given capacitor depends on its geometry and on the material—called a dielectric— that separates the conductors.

Figure 26.1 A capacitor consists of two conductors. When the capacitor is charged, the conductors carry charges of equal magnitude and opposite sign.

26.1

Definition of Capacitance

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PITFALL PREVENTION

26.1 Capacitance Is a Capacity
To understand capacitance, think of similar notions that use a similar word. The capacity of a milk carton is the volume of milk that it can store. The heat capacity of an object is the