Chapter 21: The Electric Field I: Discrete Charge Distributions

1. Chapter 21: The Electric Field I: Discrete Charge Distributions Section 21-1: Charge

2. Electric charges of the same sign • attract each other. • repel each other. • exert no forces on each other.

3. Electric charges of the same sign • attract each other. • repel each other. • exert no forces on each other.

4. Electric charges of the opposite sign • attract each other. • exert no forces on each other. • repel each other.

5. Electric charges of the opposite sign • attract each other. • exert no forces on each other. • repel each other.

6. Electrons • are about 2000 times more massive than protons. • are about 2000 times less massive than protons. • have about 2000 times more charge than protons. • have about 2000 times less charge than protons. • can have any amount of charge.

7. Electrons • are about 2000 times more massive than protons. • are about 2000 times less massive than protons. • have about 2000 times more charge than protons. • have about 2000 times less charge than protons. • can have any amount of charge.

8. Protons • are about 2000 times more massive than electrons. • are about 2000 times less massive than electrons. • have about 2000 times more charge than electrons. • have about 2000 times less charge than electrons. • can have any amount of charge.

9. Protons • are about 2000 times more massive than electrons. • are about 2000 times less massive than electrons. • have about 2000 times more charge than electrons. • have about 2000 times less charge than electrons. • can have any amount of charge.

10. Experimental evidence indicates that • charge is quantized and conserved. • charge is quantized but not conserved. • charge is conserved but not quantized. • charge is neither quantized nor conserved.

11. Experimental evidence indicates that • charge is quantized and conserved. • charge is quantized but not conserved. • charge is conserved but not quantized. • charge is neither quantized nor conserved.

12. An electron (q = e) and a positron (q = e) can combine to give off two gamma rays. The net change in the algebraic sum of the charges before and after the combination is • +2e • zero • 2e • +e • e

13. An electron (q = e) and a positron (q = e) can combine to give off two gamma rays. The net change in the algebraic sum of the charges before and after the combination is • +2e • zero • 2e • +e • e

14. How many electrons must be transferred to a body to produce a charge of 125 nC? • 1.25 ´ 10–7 • 1.60 ´ 10–19 • 1.28 ´ 1012 • 3.45 ´ 1011 • 7.81 ´ 1011

15. How many electrons must be transferred to a body to produce a charge of 125 nC? • 1.25 ´ 10–7 • 1.60 ´ 10–19 • 1.28 ´ 1012 • 3.45 ´ 1011 • 7.81 ´ 1011

16. A particular nucleus of the element erbium contains 68 protons and 90 neutrons. What is the total number of electrons in the neutral erbium atom? • 90 • 158 • 22 • 68 • None of the above

17. A particular nucleus of the element erbium contains 68 protons and 90 neutrons. What is the total number of electrons in the neutral erbium atom? • 90 • 158 • 22 • 68 • None of the above

18. Chapter 21: The Electric Field I: Discrete Charge Distributions Section 21-2: Conductors and Insulators and Concept Check 21-1a, 21-1b and 21-2

19. Two identical conducting spheres, one that has an initial charge +Q, the other initially uncharged, are brought into contact. What is the new charge on each sphere? • −Q • −Q/2 • zero • +Q/2 • +Q

20. Two identical conducting spheres, one that has an initial charge +Q, the other initially uncharged, are brought into contact. What is the new charge on each sphere? • −Q • −Q/2 • zero • +Q/2 • +Q

21. Two identical conducting spheres, one that has an initial charge +Q, the other initially uncharged, are brought into contact. While the spheres are in contact, a positively charged rod is moved close to one sphere, causing a redistribution of the charges on the two spheres so the charge on the sphere closest to the rod has a charge of −Q. What is the charge on the other sphere? • −2Q • −Q • zero • +Q • +2Q

22. Two identical conducting spheres, one that has an initial charge +Q, the other initially uncharged, are brought into contact. While the spheres are in contact, a positively charged rod is moved close to one sphere, causing a redistribution of the charges on the two spheres so the charge on the sphere closest to the rod has a charge of −Q. What is the charge on the other sphere? • −2Q • −Q • zero • +Q • +2Q

23. Two identical conducting spheres are charged by induction and then separated by a large distance; sphere 1 has charge +Q and sphere 2 has charge −Q. A third identical sphere is initially uncharged. If sphere 3 is touched to sphere 1 and separated, then touched to sphere 2 and separated, what is the final charge on each of the three spheres? • Q1 = +Q/4, Q2 = +Q/4, Q3 = −Q/2 • Q1 = −Q/2, Q2 = +Q/4, Q3 = +Q/4 • Q1 = +Q/2, Q2 = −Q/4, Q3 = −Q/4 • Q1 = −Q/4, Q2 = −Q/2, Q3 = −Q/2 • Q1 = −Q/2, Q2 = +Q/2, Q3 = +Q/2

24. Two identical conducting spheres are charged by induction and then separated by a large distance; sphere 1 has charge +Q and sphere 2 has charge −Q. A third identical sphere is initially uncharged. If sphere 3 is touched to sphere 1 and separated, then touched to sphere 2 and separated, what is the final charge on each of the three spheres? • Q1 = +Q/4, Q2 = +Q/4, Q3 = −Q/2 • Q1 = −Q/2, Q2 = +Q/4, Q3 = +Q/4 • Q1 = +Q/2, Q2 = −Q/4, Q3 = −Q/4 • Q1 = −Q/4, Q2 = −Q/2, Q3 = −Q/2 • Q1 = −Q/2, Q2 = +Q/2, Q3 = +Q/2

25. Two small spheres attract one another electrostatically. This can occur for a variety of reasons. Which of the following statements is true? • At least one sphere must be charged. • Neither sphere need be charged. • Both spheres must be charged and the charges must have the same sign. • Both spheres must be charged and the charges must have opposite signs.

26. Two small spheres attract one another electrostatically. This can occur for a variety of reasons. Which of the following statements is true? • At least one sphere must be charged. • Neither sphere need be charged. • Both spheres must be charged and the charges must have the same sign. • Both spheres must be charged and the charges must have opposite signs.

27. Two small spheres repel one another electrostatically. Which of the following statements is true? • At least one sphere must be charged. • Neither sphere need be charged. • Both spheres must be charged and the charges must have the same sign. • Both spheres must be charged and the charges must have opposite signs.

28. Two small spheres repel one another electrostatically. Which of the following statements is true? • At least one sphere must be charged. • Neither sphere need be charged. • Both spheres must be charged and the charges must have the same sign. • Both spheres must be charged and the charges must have opposite signs.

29. If you bring a positively charged insulator near two uncharged metallic spheres that are in contact and then separate the spheres, the sphere on the right will have • no net charge. • a positive charge. • a negative charge.

30. If you bring a positively charged insulator near two uncharged metallic spheres that are in contact and then separate the spheres, the sphere on the right will have • no net charge. • a positive charge. • a negative charge.

31. If you bring a negatively charged insulator near two uncharged metallic spheres that are in contact and then separate the spheres, the sphere on the right will have • no net charge. • a positive charge. • a negative charge.

32. If you bring a negatively charged insulator near two uncharged metallic spheres that are in contact and then separate the spheres, the sphere on the right will have • no net charge. • a positive charge. • a negative charge.

33. A uniformly positively charged spherical conductor is placed midway between two identical uncharged conducting spheres. How would the charges in the middle sphere be distributed? • The positive charges stay uniformly distributed on the surface of the middle sphere. • There are more positive charges near the top and bottom of the sphere compared to the sides next to the two other spheres. • There are more positive charges near the sides of the spheres that are next to the other two spheres compared to the other regions of the sphere. • There are more positive charges near the front and back of the sphere compared to the sides next to the two other spheres. • None of these is correct.

34. A uniformly positively charged spherical conductor is placed midway between two identical uncharged conducting spheres. How would the charges in the middle sphere be distributed? • The positive charges stay uniformly distributed on the surface of the middle sphere. • There are more positive charges near the top and bottom of the sphere compared to the sides next to the two other spheres. • There are more positive charges near the sides of the spheres that are next to the other two spheres compared to the other regions of the sphere. • There are more positive charges near the front and back of the sphere compared to the sides next to the two other spheres. • None of these is correct.

35. Chapter 21: The Electric Field I: Discrete Charge Distributions Section 21-3: Coulomb’s Law

36. Two small spheres, each with mass m = 5.0 g and charge q, are suspended from a point by threads of length L = 0.30 m. What is the charge on each sphere if the threads make an angle theta of 20º with respect to the vertical? • 7.9 × 10–7 C • 2.9 × 10–7 C • 7.5 × 10–2 C • 6.3 × 10–13 C • 1.8 × 10–7 C

37. Two small spheres, each with mass m = 5.0 g and charge q, are suspended from a point by threads of length L = 0.30 m. What is the charge on each sphere if the threads make an angle theta of 20º with respect to the vertical? • 7.9 × 10–7 C • 2.9 × 10–7 C • 7.5 × 10–2 C • 6.3 × 10–13 C • 1.8 × 10–7 C

38. Three charges +q, +Q, and –Q are placed at the corners of an equilateral triangle as shown. The net force on charge +q due to the other two charges is • up. • down. • along a diagonal. • to the left. • to the right.

39. Three charges +q, +Q, and –Q are placed at the corners of an equilateral triangle as shown. The net force on charge +q due to the other two charges is • up. • down. • along a diagonal. • to the left. • to the right.

40. Charges q1 and q2 exert repulsive forces of 10 N on each other. What is the repulsive force when their separation is decreased so that their final separation is 80% of their initial separation? • 16 N • 12 N • 10 N • 8.0 N • 6.4 N

41. Charges q1 and q2 exert repulsive forces of 10 N on each other. What is the repulsive force when their separation is decreased so that their final separation is 80% of their initial separation? • 16 N • 12 N • 10 N • 8.0 N • 6.4 N

42. A proton is about 2000 times more massive that an electron but they both have charges of the same magnitude. The magnitude of the force on an electron by a proton is ____ the magnitude of the force on the proton by the electron. • greater than • equal to • less than

43. A proton is about 2000 times more massive that an electron but they both have charges of the same magnitude. The magnitude of the force on an electron by a proton is ____ the magnitude of the force on the proton by the electron. • greater than • equal to • less than

44. The Coulomb’s force between a proton and an electron is 2.271039 times greater than the gravitational force between them. If the two forces were equal, what should the size of the elementary charge be? • 1.60  10-19 C • 3.36  10-39 C • 1.23  10-77 C • 2.27  10-39 C • 4.41  10-40 C

45. The Coulomb’s force between a proton and an electron is 2.271039 times greater than the gravitational force between them. If the two forces were equal, what should the size of the elementary charge be? • 1.60  10-19 C • 3.36  10-39 C • 1.23  10-77 C • 2.27  10-39 C • 4.41  10-40 C

46. A charge 2Q is located at the origin while a second charge Q is located at x = a. Where should a third charge be placed so that the net force on this third charge is zero? • x < 0 • 0 < x < a • x > a • x < 0 or 0 < x < a • 0 < x < a or x > a

47. A charge 2Q is located at the origin while a second charge Q is located at x = a. Where should a third charge be placed so that the net force on this third charge is zero? • x < 0 • 0 < x < a • x > a • x < 0 or 0 < x < a • 0 < x < a or x > a

48. The force between two very small charged bodies is found to be F. If the distance between them is doubled without altering their charges, the force between them becomes • F/2 • 2F • F/4 • 4F • 1/F 2

49. The force between two very small charged bodies is found to be F. If the distance between them is doubled without altering their charges, the force between them becomes • F/2 • 2F • F/4 • 4F • 1/F 2

50. The force between two very small charged bodies is found to be F. If the distance between them is tripled without altering their charges, the force between them becomes • 9F • 3F • F/3 • F/9 • 1/F 3