solutions_chapter17 - 17 ELECTRIC CHARGE AND ELECTRIC FIELD...

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17-1 E LECTRIC C HARGE AND E LECTRIC F IELD 17 Answers to Multiple-Choice Problems 1. D 2. C 3. C 4. B, C 5. E 6. B 7. C 8. A 9. B 10. B 11. D 12. A 13. B 14. C 15. A Solutions to Problems 17.1. Set Up: Unlike charges attract and like charges repel. In a conductor some of the negative charge is free to move. In an insulator the charge can shift position only slightly. Solve: (a) Aluminum is a conductor and negative charge in the sphere moves away from the rod. The distribution of charge is sketched in Figure 17.1a. (b) The charges in the nonconducting sphere displace slightly, with negative charge moving away from the rod. The distribution of charge is sketched in Figure 17.1b. Figure 17.1 17.2. Set Up: Copper is a conductor, so some of the electrons are free to move. The positive charge on the rod attracts the negative charge in the ball. When the ball is connected to the earth by a conducting wire, charge can flow between the ball and the earth. Solve: (a) Electrons move toward the rod. The distribution of charge is sketched in Figure 17.2a. (b) Electrons from the earth are attracted by the region of positive charge on the ball and flow onto the ball, giving it a net negative charge. When the rod is removed, this net charge distributes uniformly over the surface of the ball, as sketched in Figure 17.2b. Figure 17.2 17.3. Set Up: For an isolated sphere, the excess charge is uniformly distributed over the surface of the conductor. Unlike charges attract and like charges repel, and in a conductor the excess charge is free to move. Solve: (a) The uniform distribution of charge over the surface of each sphere is sketched in Figure 17.3a. (b) When the spheres are close to each other, the negative and positive excess charges are drawn toward each other, as shown in Figure 17.3b. (a) (b) (a) (b)
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(c) When the spheres are close to each other, the excess negative charges on each sphere repel, as shown in Fig- ure 17.3c. Figure 17.3 Reflect: We will learn later in the chapter that the excess charge on a conductor is on the surface of the conductor. 17.4. Set Up: Unlike charges attract and in a conductor the excess charge is free to move. Solve: Negative charge in the earth is pulled to the surface beneath the charged cloud, as sketched in Figure 17.4. Figure 17.4 17.5. Set Up: The charge of one electron is Solve: (a) (b) 17.6. Set Up: The total charge is the number if ions times the charge of each. Solve: 17.7. Set Up: Charge conservation requires that the total charge Q of the reactants equals the total charge of the products. and has charge and each have charge Solve: (a) reactants: products Could not occur. (b) reactants: products Could occur. (c) reactants: products Could not occur. (d) reactants: products Could not occur. (e) reactants: products Could occur. Reflect: Just because the reaction obeys charge conservation doesn’t mean it actually occurs. There could be other reasons why the reaction does not occur.
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