Electricity Final Unit Final Assessment Name k = 1/ (4pe 0 ) = 9.0 10 9 N m 2 C -2 mass of an electron = 9.11 10-31 kg mass of a proton = 1.67 10-27 kg G = 6.67 10-11 N m 2 kg -2 C = 3 x10 8 m/s Show all your work. Partial credit is available on most questions. If a question does not make sense to you, come ask me! Good luck. 1. What is the force of repulsion between two electrons held one meter apart in a vacuum? What is the gravitational force of attraction between them? By what factor is the electric repulsion greater than the gravitational attraction? 2. In which way is the electric force similar to the gravitational force? A. Electric force is proportional to the mass of the object. B. Electric force is similar in strength to gravitational force. C. Electric force is both attractive and repulsive. D. Electric force decreases in strength as the distance between the charges increases. 3. A negatively charged balloon has 3.5 µc of charge. How many excess electrons are on this balloon?
4. According to Newton s third law, every action has an equal and opposite reaction. When a comb is charged and held near small pieces of paper, the comb exerts an electric force on the paper pieces and pulls them toward it. Why don t you observe the comb moving toward the paper pieces as well? 5. At the point of fission, a nucleus of 235U that has 92 protons is divided into two smaller spheres, each of which has 46 protons and a radius of 5.90 10 15 m. What is the magnitude of the repulsive force pushing these two spheres apart? 6. Three positive point charges of 3.0 nc, 6.0 nc, and 2.0 nc, respectively, are arranged in a triangular pattern, as shown below. Find the magnitude and direction of the electric force acting on the 6.0 nc charge. 7. Draw some representative electric field lines for two charges of +q and 3q separated by a small distance
8. Find the electric field at a point midway between two charges of +30.0 10 9 C and +60.0 10 9 C separated by a distance of 30.0 cm. 9. The moon (m = 7.36 10 22 kg) is bound to Earth (m = 5.98 10 24 kg) by gravity. If, instead, the force of attraction were the result of each having a charge of the same magnitude but opposite in sign, find the quantity of charge that would have to be placed on each to produce the required force. 10. Consider an electron that is released from rest in a uniform electric field. a. If the electron is accelerated to 1.0 percent of the speed of light after traveling 2.0 mm, what is the strength of the electric field? b. What speed does the electron have after traveling 4.0 mm from rest?
Use the graph below to answer questions 11 14. The graph shows the electric field strength at different distances from the center of the charged conducting sphere of a Van de Graaff generator. 11. What is the electric field strength 2.0 m from the center of the conducting sphere? A. 0 N/C B. 5.0 10 2 N/C C. 5.0 10 3 N/C D. 7.2 10 3 N/C 12. What is the strength of the electric field at the surface of the conducting sphere? A. 0 N/C B. 1.5 10 2 N/C C. 2.0 10 2 N/C D. 7.2 10 3 N/C 13. What is the strength of the electric field inside the conducting sphere? A. 0 N/C B. 1.5 10 2 N/C C. 2.0 10 2 N/C D. 7.2 10 3 N/C 14. What is the radius of the conducting sphere? A. 0.5 m B. 1.0 m C. 1.5 m D. 2.0 m
15. An electric heater works by passing a current of 100 A though a coiled metal wire, making it red hot. If the resistance of the wire is 1.1 ohms, what voltage must be applied to it? Use the diagram below to answer the question 16-18. 16. What is the total voltage in each circuit? 17. How much current would be measured in each circuit if the light bulb has a resistance of 6 ohms? 18. How much current would be measured in each circuit if the light bulb has a resistance of 12 ohms? 19. A toaster oven is plugged into an outlet that provides a voltage difference of 120 V. What power does the oven use if the current is 10A? 20. The current flowing in an appliance connected to a 120 V source is 2 A. How many kilowatt-hours of electrical energy does the appliance use in 4 h?
21. Determine what the four voltmeters (A, B, C, D) will register when connected to the circuit below in the following positions (assume a battery voltage of 6 volts): 22. Calculate the amount of voltage dropped across resistor R 2 in diagram below:
23. In circuit below, three resistors receive the same amount of voltage (24 volts) from a single source. Calculate the amount of current "drawn" by each resistor, as well as the amount of power dissipated by each resistor: 24. One deterrent to burglary is to leave your front porch light on all the time. If your fixture contains a 60W bulb and your local power utility sells energy at 8 cents per kilowatt hour, how much will it cost to leave the bulb on for a 30-day month?
KEY 1. F = kq 1 Q 2 /r 2 = (9.0 x 10 9 x 1.6 x 10-19 x 1.6 x 10-19 )/ 1 2 = 2.3 x 10-28 N F = Gm 1 m 2 /r 2 = (6.67 x 10-11 x 9.11 x 10-31 x 9.11 x 10-31 )/ 1 2 = 5.5 x 10-71 N Electrical force/gravitational force = 2.3 x 10-28 / 5.5 x 10-71 = 4 x 10 42 2. D 3. 2.2 10 13 electrons 4. The comb has a significantly greater mass, so its acceleration is much less. 5. 3.50 10 3 N 6. 1.00 10 7 N, 12 below the positive x-axis 7. Lines should originate from the +q charge and end on the 3q charge, and the ratio of lines from +q to lines ending on 3q should be 1/3 8. 12.0 103 N/C, toward the 30.0 10 9 C charge 9. 5.72 10 13 C 10. a. 1.3 10 4 N/C b. 4.2 10 6 m/s 11. B 12. D 13. A 14. A 15. 110V 16. 6V, 12V 17. 1A, 2A 18. 0.5A, 1A 19. 1200W 20. 0.96kWh 21. A: 0V, B: 6V, C: 6V, D: 0V 22. 12.11V 23. I 1 Ω = 24 amps I 2 Ω = 12 amps I 3 Ω = 8 amps P 1 Ω = 576 watts P 2 Ω = 288 watts P 3 Ω = 192 watts 24. $3.456