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2.1: Introduction
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This section provides an introduction to the chapter on electric charges, fields, and forces.
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2.2: Electric Charge Model
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You are certainly familiar with electronic devices that you activate with the click of a switch, from computers to cell phones to television. And you have certainly seen electricity in a flash of lightning during a heavy thunderstorm. But you have also most likely experienced electrical effects in other ways, maybe without realizing that an electric force was involved. Let’s take a look at some of these activities and see what we can learn from them about electric charges and forces.
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2.3: Conduction and Charging
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In the preceding section, we said that scientists were able to create electric charge only on nonmetallic materials and never on metals. To understand why this is the case, you have to understand more about the nature and structure of atoms. In this section, we discuss how and why electric charges do—or do not—move through materials. A more complete description is given in a later chapter.
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2.4: Electric Fields and Forces
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Each electric charge is associated with an electric field. The electric field only depends on the configuration and size of the source charges. Once the electric field is found, it allows us to calculate the force on any test charge. The electric force between two point charges is described by Coulomb's Law.
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2.5: Electric Fields and Forces with Multiple Charges
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Experiments with electric charges have shown that if two objects each have electric charge, then they exert an electric force on each other. The magnitude of the force is linearly proportional to the net charge on each object and inversely proportional to the square of the distance between them. (Interestingly, the force does not depend on the mass of the objects.) The direction of the force vector is along the imaginary line joining the two objects and is dictated by the signs of the charges.
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2.6: Electric Field Diagrams
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Our model is that the charge on an object (the source charge) alters space in the region around it in such a way that when another charged object (the test charge) is placed in that region of space, that test charge experiences an electric force. Electric field-vector diagrams and field-line diagrams enable us to visualize the field.
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2.7: Common Models of Electric Field
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Many practical scenarios contain so many individual charges that they can be effectively considered as a continuous distribution of charge. This section will summarize the electric fields that result from some common geometries of charge distribution, including a finite line, infinite line, ring, disk, and infinite plane.
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2.8: Motion of a Charged Particle in an Electric Field
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When a charged particle is placed in an electri field, the field causes an electric force on the particle. The electric force then causes particle motion. In the case that the electric field is uniform, kinematics can be used to calculate the position and velocity of the charged particle.
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2.9: Conclusion
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This section concludes the chapter and provides connections to the next chapter.
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2.10: The Electric Field (Summary)
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This section provides a glossary and summary of key points.
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2.11: The Electric Field (Exercises)
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This section provides a set of exercises for the chapter.
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2.12: The Electric Field (Answers)
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This section provides the answers to the odd-numbered conceptual questions and problems.