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Name:_____________________________ K/U- /10 C- /10 A- /18 T/I- /10 Gravitational, Electric and Magnetic Fields - SPH4U1 Multiple Choice Identify the letter of the choice that best completes the statement or answers the question. ____ ____ ____ ____ ____ ____ 1. Which statement best describes differences and similarities among electrostatic force, magnetic force, and gravitational force? a. All three follow the inverse square law, with electrostatic force and magnetic force needing two poles or charges. b. Magnetic force and gravitational force follow the inverse square law, with electrostatic force needing two opposite charges. c. All three require opposite poles or charges, but only gravitational force follows the inverse square law. d. Electrostatic force and gravitational force have associated fields, but magnetic force does not. e. Gravitational force is stronger than electrostatic force, and both follow the inverse square law. 2. To investigate electric field intensity, a test charge must be used. What charge is required? a. 0 C b. 1.0 C c. 1.6 1019 C d. same as the charge for an electron (but could be positive) e. none of the above 3. Which statement best explains why the gravitational field intensity changes from position to position on Earth’s surface. a. The Moon and the Sun affect Earth’s gravity. b. Earth is not a perfect sphere, and the distance to the centre varies. c. Earth is not a perfect sphere, the distance to the centre varies, and there is an inertial effect because of Earth’s rotation. d. Some surface features on Earth are denser than others and cause a greater effect on gravity in the local area. e. Earth cannot be considered a true point source for gravity. 4. Carrie and Anne use different-sized test charges in an unchanging electric field. Carrie uses twice the charge of Anne. What does Anne find? a. the same field as Carrie b. a stronger field than Carrie c. a weaker field than Carrie d. a difference determined by the mass of the test charges e. a difference determined by the charge of the test charges 5. Why is a very small amount of charge used for a test charge? a. because it moves easily b. because it is easy to calculate c. so it will not influence the electric field intensity too much d. so it can only be influenced by one other charge object e. so it is not affected by the inverse square law 6. A charged particle is placed at rest in a magnetic field. What will the particle do? a. accelerate b. stay at rest c. move at a constant speed d. come to rest between magnetic lines of force e. none of the above Name:_____________________________ ____ 7. What is the convention for the direction of a magnetic field? a. directed out from the North Pole b. directed out from the South Pole c. determined by the direction of the electric field d. determined by the number of atoms lined up magnetically e. determined by the position of the monopole ____ 8. Which statement describes how a positively charged particle, placed between two oppositely charged plates, will behave? a. It will remain stationary. b. It will move toward the negative plate at a constant speed. c. It will accelerate toward the negative plate. d. It will move parallel to the plates. e. It will move against the direction of the electric field. ____ 9. Which property is observed when a beam of charged particles is fired into a magnetic field? a. If the beam of charged particles is parallel to the magnetic field, no deflection will occur. b. The maximum deflection happens when the beam is perpendicular to the magnetic field. c. The magnitude of the magnetic deflecting force is directly proportional to the magnitude of the charge on each particle. d. The magnetic deflecting force is always perpendicular to the direction of travel of the charge and to the magnetic field. e. all of the above ____ 10. Electrons are moving south, through a uniform magnetic field that is also directed south. What happens to the electrons? a. They speed up. b. They turn to the right. c. They slow down. d. They are not be affected by the field. e. They turn to the left. Short Answer For the following questions, write the most appropriate answer in the space provided. 11. Compare the conventions used for directions of field lines in gravitational, magnetic, and electric fields. (3 M) 2 Name:_____________________________ 12. Why can magnetic field intensity not be described/tested in the same way as gravitational or electrostatic field intensity? (3 M) 13. Why are magnetic fields and electric fields used in particle accelerators? (2 M) 14. The following diagram shows a field around a single charged particle with an invisible companion. Add the invisible companion and its field. (2 M) 3 Name:_____________________________ Problem Solving For the following questions, write the answer in the space provided. If the question requires mathematical calculations, show all of your work. 15. Each side of a vertical right-angled isosceles triangle measures 1.87 cm. Three charged objects are placed at the vertices (corners) of the triangle. Each of the two objects at the vertices of the base has a charge of +5.00 C. The object at the top vertex (right angle) of the triangle has a charge of +4.74 C. What is the net force on theobject at the top vertex? (4 M) 16. Two objects, with charges of 3.9 C and +5.3 C, are placed 21.0 cm apart. What is the electrostatic force between these objects? (3 M) 17. A wire, 20.0 cm long, is placed in a uniform magnetic field at an angle of 45 to the field. The field strength is 5.0 T. What is the force on the wire if it is carrying a current of 3.0 A? (3 M) 4 Name:_____________________________ 18. A wire is carrying a current of 3.27 A through a uniform magnetic field of 1.73 T. The force on the wire is 6.314 N. What is the length of the wire? (3 M) 19. Find the electric field intensity around a positively charged particle at point X in the following diagram. (5 M) 5 Name:_____________________________ Critical Thinking/Applications For the following questions, write the answer in the space provided. Use complete sentences in your answer. If the question requires mathematical calculations, show all of your work. Write a final statement that gives your solution. 20. The strength of the electric field between two parallel charged plates is uniform, whereas the field around a single source falls off with the square of the distance. Explain how this can be illustrated by each of the following situations? (Use the necessary diagrams in your answer) a) the shape of the field lines for a single positive source, compared with the shape of the field lines of the plates. (3 M) b) the velocity of a positive test charge placed next to the single source, compared with the velocity of a positive test charge placed next to the positive plate. (3 M) 21. Some fish produce a dipole electric field to detect other organisms, such as predators and prey in their environment. From what you know about an electric field, how does this work? (2 M) 22. At what angle must a charged particle move, with respect to a magnetic field, for the field to have the maximum force on it? Explain using the formula as a proof. (2 M) 6 Name:_____________________________ Unit Test 3 Answer Section MULTIPLE CHOICE 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. ANS: ANS: ANS: ANS: ANS: ANS: ANS: ANS: ANS: ANS: A E B A C A A C E D DIF: DIF: DIF: DIF: DIF: DIF: DIF: DIF: DIF: DIF: easy average difficult average easy easy easy average average easy REF: REF: REF: REF: REF: REF: REF: REF: REF: REF: K/U K/U K/U K/U K/U K/U K/U K/U K/U K/U LOC: LOC: LOC: LOC: LOC: LOC: LOC: LOC: LOC: LOC: EG 1.01, EG 1.02, EG 1.04 EG 1.01, EG 1.06 EG 1.01, EG 1.02, EG 1.03 EG 1.01 EG 1.01, EG 1.04 EG 1.01, EG 1.04, EG 1.08 EG 1.01, EG 1.04 EG 1.01 EG 1.01, EG 1.08 EG 1.06 SHORT ANSWER 11. ANS: Magnetic and electric field lines emanate from a point (north and positive, respectively) and terminate at a point (south and negative, respectively). Gravitational field lines terminate at a mass but do not emanate from a source point. DIF: easy REF: K/U, C LOC: EG 1.01, EG 1.04, EG 1.06 12. ANS: A source particle (such as a charged particle or a particle with mass) for magnetism (magnetic monopole) has not been found. DIF: easy REF: K/U LOC: EG 1.01, EG 1.04, EG 1.06 13. ANS: Electric fields are used to accelerate the charged particles. Electric fields and magnetic fields are both used to guide and direct the charged particles. DIF: easy REF: K/U LOC: EG 1.07 14. ANS: 7 Name:_____________________________ 15. ANS: Vector Sum = = 8.50 102 N[Up] DIF: average 16. ANS: DIF: REF: K/U, I LOC: EG 1.01, EG 1.03, EG 1.04, EG 1.06 easy REF: K/U, I LOC: EG 1.01, EG 1.03, EG 1.04, EG 1.06 average REF: K/U LOC: EG 1.05, EG 1.06, SPHU V.11 average REF: K/U LOC: EG 1.01, EG 1.06 17. ANS: DIF: 18. ANS: DIF: 8 Name:_____________________________ 19. ANS: Assume a positive charge. 1.83 103 1.467 103 cos 23.4 2.693 103 N/C 0 1.467 103 sin 23.41.33 103 5.317 103 N/C Direction: Fnet 5.96 103 N/C [up 24.3 left] DIF: average REF: I LOC: EG 1.01, EG 1.06 9 Name:_____________________________ PROBLEM 20. ANS: a) The field lines around the single source move radially outward such that the distance between them increases, indicating decreasing field strength. The field lines between the plates are parallel, indicating constant strength. b) A test charge that is placed next to a single source will move outward with a decreasing acceleration as the electric force on it decreases with distance. A test charge that is placed next to the positive plate will move to the negative plate with constant acceleration since the force on it is constant. DIF: average REF: K/U, MC LOC: EG 3.01, EG 3.02 21. ANS: Charges affect the field that is produced by the fish. Since the nervous systems of other organisms constitute moving charges, they affect the electric field. The resulting change is detectable. The amount of the change could indicate the size of the other organism, and this could help the fish distinguish predator from prey. DIF: average 22. ANS: 90 DIF: easy REF: K/U, C, MC LOC: EG 1.01, EG 1.04, EG 3.01 REF: K/U LOC: EG 1.08 10