Chapter 19 Review Current and Resistance. 1. A current of 2 amps flows for 30 seconds. How much...
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Transcript of Chapter 19 Review Current and Resistance. 1. A current of 2 amps flows for 30 seconds. How much...
![Page 1: Chapter 19 Review Current and Resistance. 1. A current of 2 amps flows for 30 seconds. How much charge is transferred?](https://reader035.fdocuments.us/reader035/viewer/2022062517/56649f305503460f94c4ba54/html5/thumbnails/1.jpg)
Chapter 19 Review
Current and Resistance
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1. A current of 2 amps flows for 30 seconds. How much charge is transferred?
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I = q/tIt = q2 x 30 = q60 C = q
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2. A charge of 10 coulombs is transmitted over a time of 20 seconds. What is the current over this period?
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I = q/tI = 10 C/20 sI = 0.5 Amps
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3. When you flip a switch to turn on a light, how long does it take the electric field in the wire to develop?
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Close to the speed of light.
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4. What is drift speed? Why is it so much slower than the speed of the electric field?
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Drift speed is the actual speed the electrons are moving in the conductor.
It is much slower because the electrons must follow a zig-zag path.
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5. What is the difference in AC and DC?
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AC is alternating current. In AC the direction of the current changes rapidly.
DC is direct current. In DC the current moves in the same direction all the time.
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6. If the current in a wire is 10 A and the resistance is 12 Ω, what is the potential difference across the circuit?
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V = IRV = 10 x 12V = 120 V
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7. A motor of resistance 5 Ω carries a current of 12 A. What is the potential difference provided by the voltage source?
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V = IRV = 12 x 5V = 60 V
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8. A light bulb with a resistance of 144 Ω is in a 120 V circuit. What is the current in the circuit?
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V =IR120 = I(144)0.833 A = I
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9. A 12 V battery is connected to a heating element. If the current is 0.5 A, what is the resistance of the heating element?
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V =IR12 = 0.5 R24 Ω = R
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10. What four factors affect the resistance of a conducting wire and what effect do they have?
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1. Length - the longer the wire, the higher the resistance2. Cross section – the “fatter” the wire, the lower the resistance3. Material – some materials are better conductors than others4. Temperature – the higher the temperature, the higher the resistance
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11. What is a superconductor? What is critical temperature?
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A superconductor is a material that will conduct electricity with zero resistance.The critical temperature is the temperature below which a superconductor has zero resistance. (These critical temperatures tend to be VERY low.)
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12. If the resistance in a circuit is doubled while the voltage is held constant, how does this change the power output of the resistor?
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By V =IR, doubling the R while V is held constant would cut I in half.By P = IV, if I is cut in half while V is held constant, the power output P is cut in half.
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13. If the voltage in a circuit is doubled while the resistance is held constant, how does this change the power output of the resistor?
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By V = IR, doubling V while R is held constant would cause I to double.By P = IV, if I is doubled and V is doubled, power output P would be quadrupled!
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14. If the current in a circuit is doubled while the resistance is held constant, how does this change the power output of the resistor?
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By V = IR, doubling I while R is held constant would cause V to double.By P = IV, if I is doubled and V is doubled, power output P would be quadrupled!
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15. If a circuit with a current of 15 A has a potential difference of 120 V, what is the power output of the circuit?
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P = IVP = 15 x 120P = 1800 W
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16. If a resistance of 240 Ω is in a 120 V circuit, what is the power output of the resistance?
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V = IR120 = I(240)I = 0.5 AP = IVP = 0.5 x 120P = 60 W
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17. A 1500 W hair dryer is plugged into a 110 V outlet. What is the current of the circuit? What is the resistance of the hair dryer?
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P = IV1500 = I(110)I = 13.6 AV = IR110 = 13.6 R8.1 Ω = R
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18. A device uses 4 A when plugged into a 120 V outlet. What is the total cost of running this device for 5 hours if the cost of energy is $0.12 per kilowatt·hour?
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P = IV P = 4 x 120P = 480 W480 W / 1000 = 0.480 kW0.480 kW x 5 hours = 2.4 kWh2.4 kWh x 12 cents =28.8 = 29 cents
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19. A device uses 6 A when plugged into a 120 V outlet. What is the total cost of running this device for 2 hours if the cost of energy is $0.11 per kilowatt·hour?
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P = IV P = 6 x 120P = 720 W720 W / 1000 = 0.720 kW0.720 kW x 2 hours = 1.44 kWh1.44 kWh x 11 cents =15.84 = 16 cents
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