Electric Fields Practice Multiple Choice

Transcription

1 Choose the best response and place your answers, using HB pencil, on the Scantron sheet provided. 1. The number of excess electrons that must be collected on a sphere to give it a charge of 5.6 x 10 6 C is: a. 9.0 x e b. 2.9 x e c. 3.5 x e d. 2.9 x e 2. Which statement defines the Law of Conservation of Electric Charge for a closed system? a. the amount of electric charge remains constant only if no reactions occur. b. the number of electrons and protons remains constant only if no reactions occur. c. the net amount of electric charge remains constant regardless of what reactions occur. d. the total number of charged objects remains constant regardless of what reactions occur. 3. Substances that prevent an electric charge from escaping are said to be: a. negatively charged b. positively charged c. insulators d. conductors 4. Which of the following statements are correct? I) The charge on a conductor accumulates at points II) In general, electrostatic charges reside entirely on the outer surface of a conductor. III) A Leyden jar may be used to store an electrostatic charge. IV) The electrophorus produces electrostatic charges by induction. a. all of the above b. II only c. II and III only d. I and IV only Use the following information for the next 2 questions Five small identical metal balls are hung from insulating silk threads and are handled only by the threads. They are not allowed to touch one another during the following experiment. It has previously been found that none of the balls is affected by a magnet, and the gravitational force between any two of the balls is negligible. Two of the balls at a time are brought near each other, and the following observations are recorded. 1. Metal balls II and V exert no force on each other. 2. Metal balls I and III repel each other. 3. All other pairs of metal balls attract one another. For example, ball I attracts balls II, IV and V 5. In which of the following pairs of balls do both balls carry charge of the same sign? a. I and II b. II and IV c. I and III d. II and V 6. In which of the following pairs of balls do the two balls could carry charge of the opposite sign? a. II and III b. III and V c. I and IV d. II and III

2 Use the following information for the next 3 questions. In the apparatus shown, electrons emitted from the hot coil move toward the first plate; those passing through the hole pass through the second plate and eventually strike the third plate. A variable voltage is applied between the second and third plates. The apparatus is enclosed in a vacuum. 7. When the variable voltage is set at 600 V, which of the graphs below best shows the acceleration (vertical axis) as a function of the distance from the hot coil? a. b. c. d.

3 8. When the variable voltage is set at 600 V, which of the graphs following best shows the velocity (vertical axis) of the electrons as a function of the distance from the hot coil? a. b. c. d. 9. Which graph below best shows the current measured by the ammeter as the variable voltage is varied from 0 V to 900 V? a. b. c. d. 10. Three identical metal balls A, B, and C are mounted on insulating rods. Ball A has a charge, q, while balls B and C are uncharged. Ball A is brought into contact momentarily with ball B, separated, and then bought in contact with ball C. At the end of this experiment, the charge on ball A will be: a. +q b. +q/2 c. +q/3 d. +q/4 11. Two small spherical clouds with charges of 1.0 C and 1.6 C repel each other with a force of 9.0 x 10 2 N. The distance separating the centres of the spheres is: a. 4.0 km b. 1.6 km c km d km

4 12. A negatively charged rod is close to the knob of the electroscope, the electroscope becomes charged: a. positively on both the knob and the leaves b. negatively on both the knob and the leaves c. positively on the knob and negatively on the leaves d. negatively on the knob and positively on the leaves 13. A negatively-charge rod is brought close to a metal sphere which is grounded. The charge on the sphere will be: a. negative, since negative charges flow from Earth to the sphere b. positive, since the negative charges on the sphere flow to Earth c. negative, since negative charges jump from the rod to the sphere d. positive, since negative charges jump from the sphere to the rod Use the following diagram for questions %LinkFirst% to %LinkLast% The charges in a thunder cloud and the ground directly beneath the cloud can develop as shown. 14. Which of the following is the most probable cause of the charge separation within the cloud? a. Rising ice crystals collide with small falling hailstones which strip electrons from the ice. b. The electrons freed from molecules by cosmic radiation fall to the cloud bottom under gravitational forces. c. The negative upper atmosphere of the earth attracts positive ions from the earth. d. Clouds rubbing against each other produce regions of positive and negative charges in each cloud.

5 15. What is the most probable cause of the charge produced on the Earth's surface? a. The cloud induces a charge separation on the ground beneath it. b. The cloud attracts protons to the ground beneath it. c. The earth is naturally positively charged. d. Other lightning bolts have attracted electrons to the other areas of the earth, leaving this area positive. 16. If a gold leaf electroscope is charged positively, and then a moderately, negatively charged rod is slowly brought near the cap of the electroscope, the leaves will now: a. slowly diverge further b. immediately diverge and later collapse c. slowly diverge and later collapse d. slowly collapse 17. The metal disc of an electrophorus can be charged repeatedly by induction without recharging the metal plate because: a. the hard rubber is charged negatively b. the electrical energy used to charge the metal disc comes mostly from grounding the disc. c. an insulating handle is used d. the metal plate contains an extremely large electrostatic charge 18. The force of repulsion between two unequal like charges is: a. directly proportional to the sum of the charges b. directly proportional to the square of each charge c. inversely proportional to the distance separating the charges d. inversely proportional to the square of the distance separating the charges 19. If a small object with a charge of 10.0 C is located 5.0 m from another small object with a charge of 10.0 C, then the electrical force between them is: a. 1.8 x N b. 2.4 x N c. 3.0 x N d. 3.6 x N 20. Two charged bodies repel each other with a force of F. The charge on one is doubled, and the charge on the other is increased by a factor of 7/3. If the distance between them is then tripled, the final resulting force would be: a. 42 F b. 14 F/3 c. 14 F/27 d. F/9

6 21. The magnitude of the force acting on Y due to X and Z is: a. 7.6 x N b. 2.2 x N c. 3.2 x N d. 2.7 x N 22. The magnitude of the force on B due to A and C is a. 5.9 x 10 7 N b. 2.4 x 10 8 N c. 2.7 x 10 8 N d. 5.0 x 10 8 N 23. A unit combination equivalent to V/m is: a. N/C b. N/A c. J/C d. J/A 24. Which of the following cannot be represented by a vector field? a. force b. impulse c. momentum d. energy 25. A charge of 2.0 x 10 6 C experiences a force of 8.0 x 10 2 N at a certain point in an electric field. The strength of the field at this point is: a. 2.0 x 10 6 N/C b. 4.0 x 10 4 N/C c. 2.5 x 10 5 N/C d. 1.6 x 10-7 N/C 26. At a point m from a point charge of magnitude 8.00 x 10-6 C, the intensity of the electric field is: a x 10-5 N/C b x 10-5 N/C c x 10 5 N/C d x 10 5 N/C 27. How does the strength of the electric field due to a charged particle vary as the distance from the particle changes? a. Directly as the distance b. Inversely as the distance c. Directly as the square of the distance d. Inversely as the square of the distance

7 28. Gravitational and electrostatic (Coulomb) forces are similar in many ways but differ in others. Which one of the following statements is not true for both gravitational and electrostatic forces? a. The force varies as 1/R 2 b. The force depends upon the quantity (mass or charge) on which the force acts c. The force can be attractive and repulsive d. The force law can be tested in the laboratory 29. One object has a positive charge, while a second object has a negative charge. The diagram that best represents the electric field surrounding the charges is: a. b. c. d. 30. R, S and T are charges of equal magnitude each located at equal distances from a point X and from each other. R and S are positive charges and T is negative. The electric field strength at X due to any one of the charges when considered separately is 2.0 N/C. Therefore, the electric field magnitude at X due to the combined effects of the three charges is most likely: a. 6.0 N/C b. 4.0 N/C c. 2.0 N/C d. 1.0 N/C 31. What change in potential difference is produced by a force that moves a charge of x 10 6 C a distance of 3.50 x 10 2 m in a direction opposite to the direction of an electric field whose intensity is 2.25 x 10 2 N/C? a V b V c V d V 32. An electron passes between two plates that are 5.0 x 10-3 m apart and that have a potential difference of 4.0 x 10 3 V between them. What is the magnitude of the force that acts on the electron? a. 1.3 x N b. 6.4 x N c. 1.3 x N d. 6.4 x N 33. An electron-volt is a unit of: a. energy b. electric potential c. voltage d. potential difference

8 34. What are the magnitudes of the electric field and the electric potential at point P midway between the two fixed charges? Magnitude of Electric Field Electrical Potential Magnitude of Electric Field Electrical Potential a. 0 N/C 0 V b. 0 N/C V c N/C 0 V d N/C V 35. If an electron is accelerated through a distance of 0.20 m across a potential difference of 5.0 x 10 2 V, its gain in kinetic energy is: a. 5.0 x 10 2 J b. 4.0 x J c. 8.0 x J d. 1.6 x J 36. If the potential difference of a field is 4.0 x 10 4 V, the speed at which an electron would emerge from this field is (assume no relativistic effects): a. 1.2 x 10 8 m/s b. 3.0 x 10 8 m/s c. 3.7 x 10 8 m/s d. 3.8 x 10 7 m/s 37. The potential difference through which an electron must be accelerated to increase its speed from rest to 1.9 x 10 7 m/s is a. 5.4 x 10-5 V b. 1.1 x 10-4 V c. 1.0 x 10 3 V d. 2.1 x 10 3 V 38. Electric current is a measure of the: a. rate at which charge passes a point b. force that moves a charge past a point c. energy required to move a charge past a point d. resistance to the movement of a charge past a point 39. If a beam of high-speed protons produced by a cyclotron is equivalent to a current of 3.2 x 10-3 A, the number of protons that will leave the cyclotron each second is: a. 2.0 x b. 6.3 x c. 2.0 x d. 5.1 x When a current of 3.0 x 10-3 A exists in a wire, the amount of charge that passes a certain point in the wire in 10 s is: a. 3.0 x 10-3 C b. 3.0 x 10-2 C c. 3.0 x 10-1 C d. 3.0 x 10 0 C

9 41. When a charge of 4.8 x C moves a distance of 2.4 x 10-1 m from point X to point Y in a uniform electric field, it gains 9.6 x J of kinetic energy. The potential difference in volts between the point X and Y is a. 2.0 x 10-9 V b. 4.0 x V c. 2.0 x 10-1 V d. 5.0 x 10-1 V 42. Electrons are released at A and pass through the openings in B and C The kinetic energy of the electrons 2.0 cm to the right of C is: a. 1.6 x J b. 1.6 x J c. 8.0 x J d. 8.0 x J 43. The electron gun in the back of a black and white TV set has a length of 1.2 x 10-2 m and an accelerating voltage of 2.0 x 10 3 V. The acceleration of the electron while in this gun is: a. 1.8 x m/s 2 b. 2.9 x m/s 2 c. 4.2 x m/s 2 d. 3.0 x 10 8 m/s A proton is accelerated to a speed of 2.0 x 10 6 m/s by a strong electric field. The proton is then stopped in 4.0 x 10 3 s. Assuming uniform deceleration, the stopping force exerted on the proton is: a. 1.4 x N b. 3.4 x N c. 8.4 x N d. 3.4 x N Use the following information for the next 2 question(s) An alpha particle, of mass m and charge q, undergoes an acceleration because of an external potential difference V has a physical quantity S associated with it. The formula for S is given by: S = 2qVm 45. When the potential difference is 7.62 x 10 4 V, the numerical value of S in SI units is: a. 3.2 x b. 1.8 x c. 4.5 x d. 4.4 x 10-7

10 46. The appropriate SI unit for S is equivalent to the SI unit for: a. force b. energy c. momentum d. magnetic field intensity 47. The acceleration of an electron in an electric field with a strength of 7.0 N/C is: a. 1.1 x m/s 2 b. 9.8 x m/s 2 c. 9.3 x m/s 2 d. 1.2 x m/s In a Millikan-type experiment using a negatively charged oil drop, the positive electric plate must be placed: a. above the negative plate b. below the negative plate c. to the left of the negative plate d. to the right of the negative plate 49. A charged oil drop of mass 1.9 x kg is suspended in a vertical electric field of strength 6.0 x 10 3 N/C. For equilibrium,the charge on the oil drop must be: a. 3.2 x C b. 3.1 x C c. 1.9 x C d. 1.1 x C 50. A negatively charged particle of mass 3.0 x kg moves horizontally through a vertical electric field of intensity 6.1 x 10 4 N/C. The number of excess electrons on the particle is: a. 0.3 b. 1 c. 3 d. 30