effectiveness Part A: Multiple Choice (6 marks) Please select the correct answer. 1. How can the electric force between two charges q1 and q2 be doubled? a. double both charges b. double the distance between the charges c. double just one of the charges d. cut the distance between the charges in half 2. Which statement describes the behaviour of a charged particle in an electric field? a. It remains at rest. b. It always accelerates in the direction of the field. c. It accelerates in the direction of the field if it is positively charged. d. It does work on the electric field as it accelerates. 3. Two plates in a Millikan apparatus are charged to 900 V and separated by a distance of 1.50 cm. What is the magnitude of the electric field between the plates? 60 000 N/C b. 1350 N/C 600 N/C d. 13.5 N/C4. Two identical electric charges q1 and q2 are separated by a distance r. If r is tripled, what happens to the electric force between them? FE FE 92 a. Triples b. decreases by a factor of 3 c. decreases by a factor of 9 d. increases by a factor of 9 5. An electric charge moves through an electric field from point P to point Q in a straight line through a distance, d. The field does 24.0 J of work on the charge. Suppose that the charge moved along a different path from P to Q through a distance of 2d. What is the work done in this case? a. 0J b. 12.0J C. 24.0J d. 48.0 J 6. A charged oil drop is at rest between the plates of a Millikan apparatus. What forces must be included on a FBD of the oil drop? a. the electric and gravitational force b. the electric, gravitational and normal force c. the electric force only d. the gravitational force only Part B: Short Answer (48 Marks) Show clear and complete solutions rounded to the correct number of significant figures. 1. A positive of charge $ 1 = U.Dis placed 12 m west of another positive charge 42 = 0.49 . A third negative charge $3 = -U. is placed 5.0 m north of $2. What is the net electric force on "2? (5 marks) 2. Two charges, one of charge +1.5 @ 10"2 C and the other of charge -2.7 @ 10" C, are 25.0 cm apart. The positive charge is to the left of the negative charge. Determine where a third charge should be located on the line connecting the two charges so that it experiences a net force of zero due to these two charges. (4 marks)3. Three point charges of 15.0 uC are arranged on the vertices of an equilateral triangle of side length 0.400m, as shown in the diagram below. Determine the net electric force experienced by charge q1 due to the other two charges. (3 marks) 91 92 4. Point charge qi has a charge of 2.5 x 10" C, and point charge q2 has a charge of 9.1 x 10-6 C. Point charge q1 is initially at rest and 0.30 m from q2. Point charge q2 has a mass of 3.8 x 10 kg. Both charges are positive with q1 remaining fixed at the origin while q2 travels to the right after being released. Determine the speed of charge q2 when it reaches a distance of 0.45 m from q1. (3 marks) 5. A positive charge Q is fixed to the origin. A negative charge with magnitude 9Q is fixed along the positive x-axis a distance d to the right of the origin. Determine a point where a small positive test charge q will experience zero electrical force from the two charges, or show that there is no such point. Include a diagram and an explanation of the placement of the test charge q. (4 marks) 6. A dust particle with a mass of 2.2 x 10"12 kg carries a negative charge due to the presence of 3500 excess electrons. It is held in position 6.0 cm from a fixed negative point charge of magnitude 4.0 x 10" C. The particle is then released and is immediately repelled. How fast will it be travelling when it is 10.0 cm from the negative point charge? (4 marks) 7. An oil drop is balanced in a Millikan apparatus. The drop has a mass of 1.8 x 10 * kg. The plates have a potential difference of 920 V, and are separated by 3.6 cm. a. Is the sphere positively or negatively charged? Explain. (1 mark) b. Calculate the magnitude of charge on the sphere. (2 marks) c. How much excess or deficit of electrons does the sphere have? (1 mark) 8. Explain, with the aid of a diagram, how an electric doorbell works. (5 marks) 9. Summarize how the principles of electricity and magnetic force are applied to make a speaker work. What role does electric current play? How is sound produced? (5 marks) 10. A positively charged object moving west on the equator experiences a magnetic force pointing up to the sky. What is the direction of the dominant magnetic field at this location? Explain. (2 marks)11. A conductor is located between the poles of a horseshoe magnet. Current flows in the direction indicated by the arrow on the diagram. Explain how to determine in which direction the conductor will move. (2 marks) horseshoe magnet 12. An electron with speed 322 m/s moves through a magnetic field of 1.9 T. The magnitude of the force on the electron is 2.73 x 10-17 N. What angle does the electron's velocity make with the magnetic field? (3 marks) 13. A particle of charge q = -4.9 microcoulombs has a speed of 620 m/s. The particle lies in the x-y plan and travels at an angle of 52 with respect to the x-axis. There is a uniform magnetic field of magnitude 1.3 T parallel to the y-axis. What are the magnitude and direction of the magnetic force on the particle? (4 marks)