Physics Electrostatics

Transcription

1 Physics Electrostatics Directions: Each of the questions or incomplete statements below is followed by five suggested answers or completions. Select the one that is best in each case and fill in the corresponding oval on the answer sheet. 1. Consider four charges, A, B, C, and D, which ehst in a region of space. Charge A attracts B, but B repels C. Charge C repels D, and D is positively charged. What is the sign of charge A? A) Positive B) Negative C) Neutral D) All of the charges are positive E) All of the charges are negative 2. Consider two charged spheres of equal size carryinra charge of +8 C and - 4 C, respectively. The spheres are brought in contact with one another for a time suffi ient to allow them to reach an equilibrium charge. They are then separated. What is the final charge on eac sphere? A) -4C B) -2C C) -1 C D) + 1 C E) +2C 3. An insulator differs from a conductor in that A) insulators are usually metals B) a conductor resists the flow of charge C) an insulator has a small number of free electrons D) an insulator has a large number of free electrons E) a conductor has more atoms than an insulator ~

2 4. A negatively charged plastic tube is brought near a neutral aluminum can sitting on its side. Which of the following statements is true? '-. ~Ube Caged ". Can A) The side of the can marked A will become positive and the can will roll toward the tube. B) The side of the can marked B will become positive and the can will roll toward the tube. C) The side of the can marked A will become negative and the can will roll away from the tube. D) The side of the can marked B will become positive and the can will roll away from the tube. E) The neutral can will not be affected by the charged tube. 5. Two conducting spheres of equal size have a charge of - 3 C and +1 C, respectively. A conducting wire is connected from the first sphere to the second. What is the new charge on each sphere? A) -4C B) +4C C) -1 C D) + 1 C E) Zero 6. Two charges qi and q2are separated by a distance r and apply a force Fto each other. If both charges are doubled, and the distance between them is halved, the new force between them is A) 1;4F B) YzF C) 4F D) 8F E) 16F 2

3 7. Two uncharged spheres A and B are near each other. A negatively charged rod is brought near one of the spheres as shown. The far right side of sphere B is 88 A) uncharged B) neutral C) positive D) negative E) equally positive and negative 8. Two charges are separated by a distance r. If one charge is doubled, and the distance between the charges is tripled to 3r, the force between the charges changes by a factor of A) 2/9 B) 4/9 C) 113 D) 2/3 E) the force is unchanged 9. Coulomb's law and Newton's law of universal gravitation both involve which ofthe following? A) The mass of the particles B) The charged of the particles C) The gravitational constant G D) The electric constant k E) The inverse square law 10. Two charges are separated by a distance r and apply an electric force of 4 newtons on each other. If one of the charges is brought closer to the other charge so that they are only half as far apart as before, the force between the two charges will be A) 1N B) 2N C) 4N D) 8N E) 16N 3

4 11. Two charges of +2 C each are placed on a line 1 meter apart. A tiny negative charge is placed at one ofthe points labeled on the diagram. At which point would the net force acting on the tiny negative charge be zero? +2C +2C -I------Ol O~f_ ABC D E A) A B) B C) C D) D E) E 12. Two charges of + 4 C and - 2 C are placed on a line 1 meter apart. A tiny positive charge is placed at one of the points labeled on the diagram. At which point would the net force acting on the tiny positive charge be zero? +4C -2C --~()~ ~()r--- A) At a point halfway between the two charges B) At a point between the charges, but closer to the negative charge C) At a point to the left of the + 4 C charge D) At a point to the right of the - 2 C charge E) None of the above 4

5 Questions Four charges are arranged in a square as shown in the figure. The center of the square is labeled with the letter C. +q C +q -q 13. Which of the following arrows best represents the direction of the net electric force acting on a tiny positive charge placed at the center of the square? A) ~ B) t C)--+ D).- E) 14. Which of the following arrows best represents the direction ofthe net electric field at the center of the square? A)! B) t C) -- D) - E) " 15. Which of the following arrows best represents the net force acting on the negative charge in the upper right corner? A) t B)! C) - D) " E) "<, 5

6 16. The electric potential at the center of the square is A) zero B) positive C) negative D) directed to the right E) directed to the left 17. Which of the following statements is true concerning the magnitude of the electric field at a point in space? A) It is a measure of the total charge on an object. B) It is a measure ofthe electric force acting on an object. C) It is a measure of the ratio of the charge on an object to its mass. D) It is a measure of the electric force per unit charge on a small test charge.. E) It is a measure of the electric force per unit mass on a small test charge. 18. Etctric field lines are always directed I A~ in the direction a negative charge would experience a force. B) in the direction a positive charge would experience a force. C] in the direction opposite to the electric force acting on any charge. D~ in the direction of electric potential. E) in the direction of attraction. I 19. I~an object is electrically neutral, we can say that it ~) attracts only negative charges Bp repels both positive and negative charges C) contains equal numbers of positive and negative charges D~ contains no electrons i) contains no protons 20. ill transfer of charge is due to the movements of 1) neutrons ~) electrons C) quarks q) protons E) atoms I 6

7 21. The arrows in the figure represent the electric field lines in a region of space. E Which of the following statements is true concerning the diagram shown in the figure? A) They could represent the electric field lines around a single positive charge. B) They could represent the electric field lines around a single negative charge. C) They could represent the electric field lines around a neutral metal sphere. D) They could represent the electric field lines between two charged parallel plates. E) They could represent the gravitational field around a large mass. 22. The electric field lines are sketched around two charges A and B as shown. What are the signs of A and B, respectively? A) Negative, negative B) Negative, positive C) Positive, positive D) Positive, negative E) Neutral, neutral 7

8 Questions The electric field for two charges is shown below. A small positive charge and a small negative charge are placed at the points shown. e+ - e o 23. The force vector acting on the small positive charge most nearly points in which direction? A)/ B) / C)~ D) 1 E) 24. The force vector acting on the small negative charge most nearly points in which direction? A)/ B) / C)~ D) 1 E) 25. Suppose that the large positive charge is C, and the small positive charge is C, and the small positive charge experiences a force of 1000 N. The strength of the electric field at the location of the small positive charge is A) 250N/C B) 500N/C C) 1000N/C D) 2000N/C E) 4000N/C 8

9 26. Two closely separated charged parallel plates are shown below The electric field lines between the plates will be directed A) to the right B) to the left C) upward D) downward E) upward and to the left 27. A positively-charged proton enters an electric field as shown. The force on the proton will be directed A) to the left B) to the right C) upward D) downward E) upward and to the left 28. A force acts on an electric charge in an electric field as shown. F +-0 E Which of the following statements must be true? A) The charge is positive. B) The charge is negative. C) The charge is neutral. D) The electric field is weak. E) The electric field is strong. 9

10 29. A positive charge enters an electric field between two charged plates and follows the path shown. '<c.::' The top plate has a charge which is A) negative B) positive C) neutral D) uncharged E) none of the above 30. The charged oil drop in Millikan's oil drop experiment was balanced between A) a gravitational force and an electric force. B) a weak nuclear force and a strong nuclear force. C) two electrical forces. D) two unlike electric fields. E) two opposite electric fields 31. Millikan's oil drop experiment established that A) the charge on any oil drop is always positive B) charge is transferred by transferring electrons C) electric charge occurs in simple multiples of the electron charge D) the charge on any oil drop is always negative E) the force between two charges follows the inverse-square law 32. The electric field strength between two charged metal plates is 8000 N/C. If the plates are a distance of 0.5 m apart, what is the potential difference between them? A) 2000 V B) 4000 V C) 8000 V D) 12,000V E) 16,000 V 10

11 Questions The figure shows three equipotentiallines for a particular charge distribution. Point A lies on a line of potential 0 volts, point B lies on a line of potential of +2 volts, and point C lies on a line of potential +4 volts. -lv v 8 c +2v +4v 33. At which point is the electric field the greatest? A) PointA B) PointB C) Point C D) The electric field is the same at all points. E) There is no electric field present. 34. Which ofthe following arrows best represents the direction ofthe electric field vector at point C? A).> B) / C) 4 D) ~ E) r 11

12 35. Suppose the distance between points B and C is 0.4 m. Assuming the electric field between points B and C is relatively constant, the magnitude of the electric field strength between points B and C is most nearly A) 0.5 V m B) 0.8 V m C) 1.6 ::{ m D) 2.0 V m E) 5.0 V m 12

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