This summary presents an abridged version of the chapter, including the important equations and all available learning aids. For convenient reference, the learning aids (including the text’s examples) are placed next to or immediately after the relevant equation or discussion.

Topic	Discussion	Learning Aids
	18.1 The Origin of Electricity
The coulomb (C)	There are two kinds of electric charge: positive and negative. The SI unit of electric charge is the coulomb (C). The magnitude of the charge on an electron or a proton is
Magnitude of charge on electron or proton
	Since the symbol e denotes a magnitude, it has no algebraic sign. Thus, the electron carries a charge of –e, and the proton carries a charge of +e.
Charge is quantized	The charge on any object, whether positive or negative, is quantized, in the sense that the charge consists of an integer number of protons or electrons.	Example 1
	18.2 Charged Objects and the Electric Force
Law of conservation of electric charge	The law of conservation of electric charge states that the net electric charge of an isolated system remains constant during any process.
Electrical repulsion and attraction	Like charges repel and unlike charges attract each other.
	18.3 Conductors and Insulators
Conductor	An electrical conductor is a material, such as copper, that conducts electric charge readily.
Insulator	An electrical insulator is a material, such as rubber, that conducts electric charge poorly.
	18.4 Charging by Contact and by Induction
Charging by contact	Charging by contact is the process of giving one object a net electric charge by placing it in contact with an object that is already charged.
Charging by induction	Charging by induction is the process of giving an object a net electric charge without touching it to a charged object.
	18.5 Coulomb’s Law
Point charge	A point charge is a charge that occupies so little space that it can be regarded as a mathematical point.
	Coulomb’s law gives the magnitude F of the electric force that two point charges q1 and q2 exert on each other:	Examples 2, 3, 4 and 5
Coulomb’s law	(18.1)	Interactive LearningWare 18.1   Concept Simulation 18.1   Interactive LearningWare 18.2
	where |q1| and |q2| are the magnitudes of the charges and have no algebraic sign. The term k is a constant and has the value k=8.99×109 N·m2/C2.The force specified by Equation 18.1 acts along the line between the two charges.	Examples 16   Interactive Solution 18.15
Permittivity of free space	The permittivity of free space e0 is defined by the relation
Use Self-Assessment Test 18.1 to evaluate your understanding of Sections 18.1, 18.2, v, 18.3, 18.4 and 18.5.
	18.6 The Electric Field
	The electric field E at a given spot is a vector and is the electrostatic force F experienced by a very small test charge q0 placed at that spot divided by the charge itself:
Electric field	(18.2)	Examples 6, 7, 8   Interactive Solution 18.65
	The direction of the electric field is the same as the direction of the force on a positive test charge. The SI unit for the electric field is the Newton per coulomb (N/C). The source of the electric field at any spot is the charged objects surrounding that spot.
	The magnitude of the electric field created by a point charge q is
Electric field of a point charge	(18.3)	Examples 9, 10, 11, 17   Interactive LearningWare 18.3   Interactive Solution 18.41
	where |q| is the magnitude of the charge and has no algebraic sign and r is the distance from the charge.
	For a parallel plate capacitor that has a charge per unit area of s on each plate, the magnitude of the electric field between the plates is
Electric field of a parallel plate capacitor	(18.4)
	18.7 Electric Field Lines
Electric field lines   Direction of electric field   Strength of electric field	Electric field lines are lines that can be thought of as a “map,” insofar as the lines provide information about the direction and strength of the electric field. The lines are directed away from positive charges and toward negative charges. The direction of the lines gives the direction of the electric field, since the electric field vector at a point is tangent to the line at that point. The electric field is strongest in regions where the number of lines per unit area passing perpendicularly through a surface is the greatest—that is, where the lines are packed together most tightly.	Example 12   Concept Simulation 18.2
	18.8 The Electric Field Inside a Conductor: Shielding
Excess charge carried by a conductor at equilibrium	Excess negative or positive charge resides on the surface of a conductor at equilibrium under electrostatic conditions. In such a situation, the electric field at any point within the conducting material is zero, and the electric field just outside the surface of the conductor is perpendicular to the surface.	Example 13
	18.9 Gauss’ Law
	The electric flux FE through a surface is related to the magnitude E of the electric field, the area A of the surface, and the angle f that specifies the direction of the field relative to the normal to the surface:
Electric flux	(18.6)
	Gauss’ law states that the electric flux through a closed surface (a Gaussian surface) is equal to the net charge Q enclosed by the surface divided by e0, the permittivity of free space:
Gauss’ law	(18.7)	Examples 14, 15   Concept Simulation 18.3   Interactive Solution 18.53
Use Self-Assessment Test 18.2 to evaluate your understanding of Sections 18.6, 18.7, 18.8 and 18.9.

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