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Current and Resistance Practice Multiple Choice Identify the choice that best completes the statement or answers the question. ____ 1. How is current affected if the time interval over which the charge passes through a given area decreases while the amount of charge remains the same? a. The current increases. b. The current decreases. c. The current initially increases and then is gradually restored. d. The current is not affected. ____ 2. The current in an electron beam in a cathode-ray tube is 7.0 10 s? a. 2.8 10 C c. 3.5 10 C b. 5.6 10 C d. 5.3 10 C ____ 3. The amount of charge that moves through the filament of a lightbulb in 2.00 s is 2.67 C. What is the current in the lightbulb? a. 5.34 A c. 0.835 A b. 1.33 A d. 0.417 A ____ 4. When electrons move through a metal conductor, a. they move in a straight line through the conductor. b. they move in zigzag patterns because of repeated collisions with the vibrating metal atoms. c. the temperature of the conductor decreases. d. they move at the speed of light in a vacuum. ____ 5. A lightbulb has a resistance of 240 when operating at 120 V. What is the current in the lightbulb? a. 2.0 A c. 0.50 A b. 1.0 A d. 0.20 A ____ 6. Which of the following wires would have the greatest resistance? a. an aluminum wire 10 cm in length and 3 cm in diameter b. an aluminum wire 5 cm in length and 3 cm in diameter c. an aluminum wire 10 cm in length and 5 cm in diameter d. an aluminum wire 5 cm in length and 5 cm in diameter ____ 7. Which of the following is the best description of a schematic diagram? a. uses pictures to represent the parts of a circuit b. determines the location of the parts of a circuit c. shows the parts of a circuit and how the parts connect to each other d. shows some of the parts that make up a circuit ____ 8. Three resistors connected in series have potential differences across them labeled V , V , and V . Which of the following expresses the potential difference taken over the three resistors together? a. Vt = V1 + V2 + V3 c. Vt = V1 = V2 = V3 A. How much charge hits the screen in 5.0 b. ____ Vt = d. Vt = 9. Three resistors connected in parallel carry currents labeled I , I , and I . Which of the following expresses the total current I in the combined system? a. It = I1 + I2 + I3 c. It = I1 = I2 = I3 b. d. It = It = ____ 10. Three resistors with values of 3.0 , 6.0 , and 12 are connected in parallel. What is the equivalent resistance of this combination? a. 0.26 c. 9.0 b. 1.7 d. 21 ____ 11. The symbol used to represent resistance in a schematic diagram is a. two straight lines. b. a single line that is broken and has a bend in it. c. one straight line. d. a zigzag line. e. none of the above ____ 12. When resistors are put in series next to each other, their overall resistance is a. the same as the resistance of one of the resistors. b. larger than the resistance of any individual resistor. c. smaller than the resistance of any of the resistors. ____ 13. As more lamps are put into a parallel circuit, the overall current in the main (through the battery) circuit a. increases. b. stays the same. c. decreases. ____ 14. Compared to the resistance of two resistors connected in series, the same two resistors connected in parallel have a. less resistance. b. more resistance. c. the same resistance. ____ 15. When one light bulb in a parallel circuit containing several light bulbs burns out, the other light bulbs a. do not burn at all. b. burn brighter. c. burn the same as before. ____ 16. In a simple parallel circuit a. voltage across each branch is the same. b. current through each resistor is inversely proportional to the resistance. c. current is divided at each branch. d. all of the above e. none of the above ____ 17. Two lamps, one with a thick filament and one with a thin filament, are connected in parallel to a battery. The voltage is greater across the lamp with the a. thin filament. b. thick filament. c. Both voltages are the same. ____ 18. Two lamps, one with a thick filament and one with a thin filament, are connected in series to a battery. The voltage is greater across the lamp with the a. thin filament. b. thick filament. c. Voltage is the same for both. ____ 19. In order for there to be a flow of charge from one place to another, there must be a a. conductor, such as a wire, connecting the two places. b. potential difference between the two places. c. Both A and B above ____ 20. An example of a voltage source is a. a dry cell. b. a generator. c. a car battery. d. rubbing a rubber rod with fur. e. all of the above ____ 21. Electrical resistance in a wire depends on the wire's a. thickness. b. conductivity. c. length. d. all of the above e. none of the above ____ 22. What is the equivalent resistance for the resistors in the figure shown above? a. 25 c. 7.5 b. 10.0 d. 5.0 Short Answer 23. What is electrical potential energy? 24. What is the source of the energy produced by a battery? 25. With regard to electric current, what is resistance? 26. Draw a schematic diagram that contains three resistors and one battery. 27. Current is not carried in the circuit shown in the schematic diagram above. Explain why this is so. 28. In the circuit shown above, what will happen when the switch is closed? Explain. Problem 29. A bolt of lightning discharges 9.6 C in 5.5 10 s. What is the average current during the discharge? 30. How much time is required for 41.34 C of charge to move through an electric juicer if the current through the juicer is 1.48 A? 31. How much current is in a resistor of 227 if the potential difference across the resistor is 145 V? 32. A potential difference of 3.6 V is placed across a resistor, producing a current of 14.3 A. What is the resistance of the resistor? 33. A 1.4 k resistor has 0.012 A of current in it. What is the potential difference across the resistor? 34. A 4.7 10 resistor carries 1.52 10 A of current. What potential difference is across the resistor? 35. Three resistors with values of 17 , 23 , 9 , respectively, are connected in series. What is their equivalent resistance? 36. A current of 0.12 A passes through a 5.1 resistor. The resistor is connected in series with a 9.1 V battery and an unknown resistor. What is the resistance value of the unknown resistor? 37. Three resistors with values of 11 , 15 , 22 , respectively, are connected in parallel. What is their equivalent resistance? 38. A 60-V potential difference is applied across a parallel combination of a 10-ohm and a 20-ohm resistor. What is the current in the 10-ohm resistor? 39. What is the equivalent resistance for the resistors in the figure shown above? 40. How much current is in one of the 10 resistors in the diagram shown above? Current and Resistance Practice Answer Section MULTIPLE CHOICE 1. ANS: A 2. ANS: C Given I = 7.0 10 t = 5.0 s PTS: 1 DIF: II OBJ: 17-3.1 DIF: IIIA OBJ: 17-3.1 DIF: IIIA PTS: 1 OBJ: 17-3.1 DIF: I OBJ: 17-3.2 DIF: PTS: PTS: PTS: OBJ: DIF: DIF: DIF: OBJ: 17-3.4 OBJ: 18-1.1 OBJ: 18-2.1 A Solution PTS: 1 3. ANS: B Given Q = 2.67 C t = 2.00 s Solution PTS: 1 4. ANS: B 5. ANS: C Given V = 120 V R = 240 Solution PTS: 6. ANS: 7. ANS: 8. ANS: 1 A C A IIIA 1 1 1 17-3.3 I I II 9. ANS: A 10. ANS: B Given R1 = 3.0 R2 = 6.0 R3 = 12 PTS: 1 DIF: II OBJ: 18-2.2 Solution 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. PTS: 1 DIF: IIIA OBJ: ANS: D PTS: 1 DIF: KEY: resistance | symbol BLM: ANS: B PTS: 1 DIF: KEY: resistor | series BLM: ANS: A PTS: 1 DIF: KEY: parallel | circuit | lamp BLM: ANS: A PTS: 1 DIF: KEY: resistance | series BLM: ANS: C PTS: 1 DIF: KEY: parallel | bulb | circuit BLM: ANS: D PTS: 1 DIF: KEY: parallel | circuit BLM: ANS: C PTS: 1 DIF: KEY: voltage | wire | parallel BLM: ANS: A PTS: 1 DIF: KEY: thick | series | voltage BLM: ANS: C PTS: 1 DIF: KEY: flow | charge BLM: ANS: E PTS: 1 DIF: KEY: voltage BLM: comprehension ANS: D PTS: 1 DIF: KEY: resistance | length BLM: ANS: B Given R1 = 8.0 R2 = 2.0 R3 = 10.0 R4 = 5.0 Solution 18-2.2 L1 OBJ: knowledge L2 OBJ: comprehension L2 OBJ: comprehension L2 OBJ: comprehension L2 OBJ: application L2 OBJ: comprehension L2 OBJ: analysis L2 OBJ: analysis L2 OBJ: comprehension L2 OBJ: 35.5 Schematic Diagrams 35.3 Series Circuits 35.4 Parallel Circuits 35.3 Series Circuits 35.4 Parallel Circuits 35.4 Parallel Circuits 35.4 Parallel Circuits 35.3 Series Circuits 34.1 Flow of Charge 34.3 Voltage Sources L2 OBJ: 34.4 Electric Resistance comprehension R1,2 = R1 + R2 = 8.0 + 2.0 = 10.0 Req = R1,2,3 + R4 = 5.00 + 5.0 = 10.0 PTS: 1 DIF: IIIA OBJ: 18-3.1 SHORT ANSWER 23. ANS: potential energy associated with a charge due to the position of the charge in an electric field. It also can be described as the amount of work done by an external agent to place a charge at a given location in an electric field PTS: 1 DIF: I OBJ: 17-1.1 24. ANS: Chemical reactions are the source of the energy in a battery. PTS: 1 DIF: I OBJ: 17-1.3 25. ANS: Resistance is the opposition to electric current by a material or device. PTS: 1 DIF: I OBJ: 17-3.3 26. ANS: Schematics should show symbols for the named circuit elements. The arrangement of the elements in either series or parallel is not important. PTS: 1 DIF: I OBJ: 18-1.1 27. ANS: There is no continuous path for current because the switch is open. PTS: 1 DIF: II OBJ: 18-1.2 28. ANS: The lamp will go out, or the lamp will get dimmer. The resistance through the switch is lower than the filament of the lamp. PTS: 1 DIF: II OBJ: 18-1.2 PROBLEM 29. ANS: 1.7 10 A Given Q 9.6 C t 5.5 10 s Solution PTS: 1 30. ANS: 27.9 s DIF: IIIA OBJ: 17-3.1 DIF: IIIB OBJ: 17-3.1 DIF: IIIA OBJ: 17-3.3 Given 1.48 A Q 41.34 C Solution PTS: 1 31. ANS: 0.639 A Given R 227 V 145 V Solution PTS: 1 32. ANS: 0.25 Given V 3.6 V I 14.3 A Solution PTS: 1 33. ANS: 17 V DIF: IIIA OBJ: 17-3.3 Given R 1.4 k 1.4 10 I 0.012 A Solution PTS: 1 34. ANS: 7.1 10 V DIF: IIIA OBJ: 17-3.3 DIF: IIIA OBJ: 17-3.3 Given R 4.7 10 I 1.52 10 A Solution PTS: 1 35. ANS: 49 Given R1 17 R2 23 R3 9 Solution For resistors in series, Req R1 + R2 + R3 PTS: 1 17 + 23 + 9 DIF: I 49 OBJ: 18-2.1 36. ANS: 71 Given I1 0.12 A R1 5.1 Vbatt 9.1 V Solution For a series circuit, I1 I2 I 0.12 A V1 R1I (5.1 )(0.12 A) 0.61 V V2 Vbatt – V1 9.1 V – 0.61 V 8.5 V PTS: 1 37. ANS: 4.93 DIF: IIIB OBJ: 18-2.1 Given R1 11 R2 15 R3 22 Solution For resistors in parallel, PTS: 1 38. ANS: 6A DIF: IIIA PTS: 1 DIF: L2 KEY: current | parallel | potential 39. ANS: 5.2 Given OBJ: 18-2.2 OBJ: 35.4 Parallel Circuits BLM: application R1 R2 R3 R4 2.0 6.0 10.0 4.0 Solution R2,3 R2 + R3 6.0 + 10.0 PTS: 1 40. ANS: 0.80 A 16.0 DIF: IIIB OBJ: 18-3.1 Given R1 2.0 R2 20.0 R3 10.0 R4 10.0 Vbatt 12 V I3 I4 Solution R V 2.0 + 4.00 R +R V PTS: 1 (R I ) 6.0 (4.00 )(2.0 A) DIF: IIIB 8.0 V OBJ: 18-3.2