Electrostatics with answers

Name: 5. ELECTROSTATICS (~12.5%)  52 Multiple Choice Questions (~4 questions on Provincial)  8 Long Answer Problems (1/2) Answers: Multiple Choice 1. 2. 3. 4. 5. 6. 7. 8. 9. a a a a d c b a b 10. c 11. c 12. c 13. a 14. d 15. c 16. c 17. b 18. b 19. b 20. c 21. d 22. d 23. d 24. c 25. c 26. b 27. b 28. c 29. d 30. b 31. b 32. c 33. c 34. a 35. b 36. a Long Answers 1. a) E= 2.50 x 103 N/C b) q= -1.60 x 10-6 C 2. E= 3.75 x 105 N/C to the right 3. V = 1.23 x 103 V 4. Q = +7.67 x 10-6 C 5. a) 2.85 x 10-15 J b) 1.85 x 106 m/s 6. a) 1.03 x 10-3 J b) Greater since the change in potential difference will be greater 7. v = 1.20 x 107 m/s 8. F = 70 N to the right 1 37. b 38. c 39. a 40. b 41. a 42. a 43. b 44. b 45. c 46. b 47. a 48. b 49. c 50. c 51. c 52. d Multiple Choice: 1. The diagram shows the electric field lines near two point charges, L and R. Identify the polarity of these point charges. 2. An electron orbits a nucleus which carries a charge of 9.6 1019 C. If the electron’s orbital radius is 2.0 1010 m, what is its electric potential energy? A. 6. 9 10 18 J B. 3. 5 10 8 J C. 43 J D. 2. 2 1011 J 3. What is the change in kinetic energy of an electron that moves from the negative plate to the positive plate in the situation shown to the right? A. B. C. D. A gain of 4.8 10 17 J A loss of 4.8 10 17 J A gain of 9. 6 10 16 J A loss of 9. 6 10 16 J 4. Two 2.0 106 C charges are positioned as shown in the diagram below. What work must be done to move a 1.2 107 C charge from location X to location Y? A. B. C. D. 3. 6 10 3 J 1. 5 10 2 J 1.8 10 2 J 3. 9 10 2 J 5. Which of the following gives correct units for electric field strength? A. V B. C C. N/m D. V/m 6. What is the final speed of an electron accelerated from rest through a potential difference of 750 V ? A. 3.8 105 m s B. 8.1 106 m s C. 1.6 107 m s D. 2.6 1014 m s 2 7. Which of the following diagrams shows the electric field in the region of two equal but opposite point charge? 8. An electron experiences an electric force of 1.8 1011 N at a distance of 5. 0 109 m from the nucleus of an ion. The electron is moved farther away, to a distance of 2.0 108 m from the ion. What is the new electric force on the electron? A. 1.11012 N B. 4.5 1012 N C. 7.2 1011 N D. 2.9 1010 N 9. What is the magnitude of the electric field at point P due to the two fixed charges as shown? A. B. C. D. 3.0 103 N/C 9.4 103 N/C 1.3 104 N/C 3.9 104 N/C 10. An electron is travelling in an electric field as shown. 3 11. A proton initially at rest is accelerated between parallel plates through a potential difference of 300 V. What is the maximum speed attained by the proton? A. 7.5 103 m/s B. 1.7 105 m/s C. 2.4 105 m/s D. 1.2 106 m/s 12. A negative charge in an electric field experiences a force accelerating it due south. What is the direction of the electric field? A. east B. west C. north D. south 13. A 2.3 106 C charge exerts a repulsive force of magnitude 0.35N on an unknown charge 0.20 m away. What are the magnitude and polarity of the unknown charge? 14. Two point charges, 2.5 106 C and -5.0 106 C , are placed 3.0m apart as shown below. What is the magnitude of the electric field at point P, midway between the two charges? A. 0 N/C B. 1.0 104 N/C C. 2.0 104 N/C D. 3.0 104 N/C 15. A 4.0109 C charge is initially located 3.0 m from a stationary 6.0108 C charge. How much work is required to move the 4.0109 C charge to a point 0.50 m from the stationary charge? A. 6.0 10 7 J B. 8.6 10 7 J C. 3.6 10 6 J 16. Two parallel plates 4.0102 m apart have a potential difference of 1000 V. An electron is released from the negative plate at the same instant that a proton is released from the positive plate. Which of the following best compares their speed and kinetic energy as they strike the opposite plate? 4 D. 4.3 10 6 J 17. Which one of the following represents correct units for electric field strength? A. T B. N/C C. J / C D. N m2/C2 18. The flow of charge per unit time defines A. power. B. current. C. voltage. D. resistance. 19. The diagram below shows two positive charges of magnitude Q and 2Q. 20. A 6.0 x 10 –6 C charge is located 4.0 m from a –3.0 x 10 –6 C charge. What is the electric potential at P, halfway between the charges? A. –4.1x10–2 V B. 6.8 x 103 V C. 1.4 x 104 V 21. Which of the following best represents the electric field between oppositely charged parallel plates? 5 D. 4.1 x 104 V 22. Three point charges of equal magnitude but opposite sign are arranged as shown in the diagram below. 23. What is the magnitude of the electric field at point P due to the two charges positioned as shown in the diagram below? A. 5.6 104 N/C B. 8.4 104 N/C C. 2.4 105 N/C D. 8.2 105 N/C 24. Which of the following diagrams best shows the electric field between two equal negative charges? 25. In a hydrogen atom, the electron and proton are separated by a distance of 5.310–11 m. What is the electric force exerted on the proton by the electron? A. 0 N B. 4. 4 10 18 N C. 8. 2 10 8 N D. 1. 0 1012 N 6 26. A 2.5 C charge is moved from a point with a potential of 12 V to another point of potential 75 V. How much work was done on this charge? A. 30 J B. 160 J C. 180 J D. 220 J 27, An object with a charge of 4.01018 C and a mass of 1.11015 kg is held stationary by balanced gravitational and electric forces midway between horizontal charged plates as shown. What is the applied voltage V? A. 16 V B. 32 V C. 65 V D. 2. 7 102 V 28. The diagram below shows a positive point charge Q. 29. A 2.0106 C charge is located halfway between an 8.0 106 C charge and a 5.0106 C charge as shown below. Find the net force on the 2.0 106 C charge. A. 1.4 10 2 N towards the left C. 5.9 10 2 N towards the left B. 1.4 10 2 N towards the right D. 5.9 10 2 N towards the right 30. What is the electric potential energy of an electron located 5.31011 m from the proton in a hydrogen atom? A. 8.2 108 J B. 4.31018 J C.2.21018 J D. 1.61019 J 31. Two long, parallel plates are separated by 0.028 m and have a potential difference between them of 80 V, as shown below. Point P is located midway between the plates. What is the potential difference between point P and one of the plates? A. 0 V B. 40 V C. 80 V D. 160 V 7 32. The diagram below shows the electric field near two point charges L and R. 33. The graphs below show potential difference V versus current I for different conductors. Which graph refers to a conductor which obeys Ohm’s Law? (Yes, this is the next unit.) 34. The electric field 2.0 m from a point charge has a magnitude of 8.0 104 N/C. What is the strength of the electric field at a distance of 4.0 m? A. 2.0104 N/C B.4.0 104 N/C C. 1.6 105 N/C D.3.2 105 N/C 35. When a charge is accelerated through a potential difference of 500 V, its kinetic energy increases from 2.0105 J to 6.0105 J . What is the magnitude of the charge? A. 4. 0 10 8 C B. 8. 0 10 8 C C. 1. 2 10 7 C 8 D. 1. 6 10 7 C 36. Which of the following correctly describes the polarity of the charges X and Y? 37. Three positive charges are fixed as shown in the diagram below. 38. A cathode ray tube beam deflects to the location as shown in Diagram I when a certain voltage is applied to the deflecting plates. The connections to the deflecting plates are then reversed and the deflecting voltage is reduced. Which location in Diagram II best represents the new beam position? A. Location 1 B. Location 2 C. Location 3 D. Location 4 9 39. Which of the following shows the electric field between two opposite charges of unequal magnitude? 40. What is the magnitude of the electric field at point P due to the two charges shown? A. 4.5103 N/C B.9.0103 N/C C.1.4104 N/C D.1.8104 N/C 41. What is the acceleration of a proton in a uniform 2.5 10 5 N/C electric field as shown below? 42. How much work is needed to move a -2.0106 C charge from position S to position T as shown below? A. 4.3102 J B. 4.8102 J C. .1x102 J D.1.1101 J 43. An electron, initially at rest, is accelerated through a potential difference of 600 V as shown. What is the maximum kinetic energy of the electron? A. 3.71031 J B. 9.61017 J C.6.0102 J 10 D.1.4104 J 44. Which of the following is an equivalent unit for the volt? A. C/s B. J/C C. N/C D. J 45. A proton is accelerated from rest between parallel plates with a potential difference of 3.0 104 V. What is the maximum speed of the proton? A. 1.3101 m/s B. 3.8105 m/s C. 2.4106 m/s D. 1.5107 m/s 46. What are the magnitude and direction of the electric force on the 2.0106 C charge shown below? 47. What is the electric potential energy of an electron at a distance of 5.31011 m from the proton in a hydrogen atom? A. 4.31018 J B.-8.2108 J C.2.7101 J D.5.11011 J 48. Two positive charges, equal in magnitude, are separated as shown below. In which location would the electric field strength be zero? A. 1 B. 2 C. 3 D. 4 49. An electron is positioned in an electric field. The force on the electron due to the electric field is equal to the force of gravity on the electron. What is the magnitude of this electric field? A. 8.931030 N/C B. 5.691012 N/C C. 5.581011 N/C D. 1.44109 N/C 11 50. Two parallel plates 6.0 10 2 m long are separated by 2.5 10 2 m and have a potential difference of 850 V. Point P is located midway between the two plates as shown below. What is the magnitude of the electric field at point P? A. 1.4104 V/ m B. 1.7104 V/m C. 3.4104 V/ m D. 6.8104 V/m 51. A particle with a charge of 2.4 105 C is accelerated from rest through a potential difference of 6.2104 V. If the final speed of this particle is 9.3103 m/s, what is the mass of the particle? A. 7.71010 kg B.5.2109 kg C.3.4108 kg D. 1.5101 kg 52. Two 3.0106 C point charges are placed 5.0 m apart as shown below. What is the potential at point P due to the two charges? A. 0 V B. 5.4103 V C. 7.6103 V D. 1.110 4 V 12 Written Problems: 1. Two charges are positioned as shown in the diagram below. a) Find the magnitude and direction of the electric field at A. (Note: 1.0 C 1.0106 C) (4 marks) b) A charge placed at A experiences a force of 4.0103 N towards the right. What are the magnitude and polarity of this charge? (3 marks) 2. Calculate the net electric field (magnitude and direction) at point P due to the two point charges shown in the diagram. (7 marks) 3. The diagram shows a small sphere of mass 1.51014 kg held in equilibrium between two parallel plates by electrostatic and gravitational forces. If the plates are 4.0103 m apart and the sphere carries a charge of magnitude 4.81019 C, what is the potential difference V between the plates? (7 marks) 4. Two point charges Q 1 and Q 2 are arranged as shown in the diagram below. The electric potential at point P due to these charges is found to be 1.9105 V. What are the magnitude and sign of charge Q1 ? (7 marks) 5. A proton is located at A, 1.0 m from a fixed +2.2106 C charge. a) What is the change in potential energy of the proton as it moves to B, 10 m from the fixed charge? (5 marks) b) If the proton started from rest at A, what would be its speed at B? (2 marks) 13 6. a.) A 2.5107 C charge is initially located 7.0 m from a fixed 8.0 106 C charge. What is the minimum amount of work required to move the 2.5107 C charge 2.0 m closer as shown? (3 marks) b) If the 2.5107 C charge is moved a further 2.0 m closer to the 8.0106 C charge, will the additional work required be less than, the same as or greater than the work required in (a)? Using principles of physics, explain your answer. (4 marks) 7.) An electron moving at 7.5106 m/s enters an electric field between parallel plates by passing through a small hole in one of the plates. What is the impact speed of the electron on the second plate? (7 marks) 8. A -4.2106 C charge is placed between two stationary charges, Q1 and Q2 , as shown below. What is the magnitude and direction of the net force on the -4.2106 C charge due to the two stationary charges? (7 marks) 14