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Chapter 19 Review Current and Resistance

Chapter 19 Review Current and Resistance. 1. A current of 2 amps flows for 30 seconds. How much charge is transferred?

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Page 1: Chapter 19 Review Current and Resistance. 1. A current of 2 amps flows for 30 seconds. How much charge is transferred?

Chapter 19 Review

Current and Resistance

Page 2: Chapter 19 Review Current and Resistance. 1. A current of 2 amps flows for 30 seconds. How much charge is transferred?

1. A current of 2 amps flows for 30 seconds. How much charge is transferred?

Page 3: Chapter 19 Review Current and Resistance. 1. A current of 2 amps flows for 30 seconds. How much charge is transferred?

I = q/tIt = q2 x 30 = q60 C = q

Page 4: Chapter 19 Review Current and Resistance. 1. A current of 2 amps flows for 30 seconds. How much charge is transferred?

2. A charge of 10 coulombs is transmitted over a time of 20 seconds. What is the current over this period?

Page 5: Chapter 19 Review Current and Resistance. 1. A current of 2 amps flows for 30 seconds. How much charge is transferred?

I = q/tI = 10 C/20 sI = 0.5 Amps

Page 6: Chapter 19 Review Current and Resistance. 1. A current of 2 amps flows for 30 seconds. How much charge is transferred?

3. When you flip a switch to turn on a light, how long does it take the electric field in the wire to develop?

Page 7: Chapter 19 Review Current and Resistance. 1. A current of 2 amps flows for 30 seconds. How much charge is transferred?

Close to the speed of light.

Page 8: Chapter 19 Review Current and Resistance. 1. A current of 2 amps flows for 30 seconds. How much charge is transferred?

4. What is drift speed? Why is it so much slower than the speed of the electric field?

Page 9: Chapter 19 Review Current and Resistance. 1. A current of 2 amps flows for 30 seconds. How much charge is transferred?

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.

Page 10: Chapter 19 Review Current and Resistance. 1. A current of 2 amps flows for 30 seconds. How much charge is transferred?

5. What is the difference in AC and DC?

Page 11: Chapter 19 Review Current and Resistance. 1. A current of 2 amps flows for 30 seconds. How much charge is transferred?

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.

Page 12: Chapter 19 Review Current and Resistance. 1. A current of 2 amps flows for 30 seconds. How much charge is transferred?

6. If the current in a wire is 10 A and the resistance is 12 Ω, what is the potential difference across the circuit?

Page 13: Chapter 19 Review Current and Resistance. 1. A current of 2 amps flows for 30 seconds. How much charge is transferred?

V = IRV = 10 x 12V = 120 V

Page 14: Chapter 19 Review Current and Resistance. 1. A current of 2 amps flows for 30 seconds. How much charge is transferred?

7. A motor of resistance 5 Ω carries a current of 12 A. What is the potential difference provided by the voltage source?

Page 15: Chapter 19 Review Current and Resistance. 1. A current of 2 amps flows for 30 seconds. How much charge is transferred?

V = IRV = 12 x 5V = 60 V

Page 16: Chapter 19 Review Current and Resistance. 1. A current of 2 amps flows for 30 seconds. How much charge is transferred?

8. A light bulb with a resistance of 144 Ω is in a 120 V circuit. What is the current in the circuit?

Page 17: Chapter 19 Review Current and Resistance. 1. A current of 2 amps flows for 30 seconds. How much charge is transferred?

V =IR120 = I(144)0.833 A = I

Page 18: Chapter 19 Review Current and Resistance. 1. A current of 2 amps flows for 30 seconds. How much charge is transferred?

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?

Page 19: Chapter 19 Review Current and Resistance. 1. A current of 2 amps flows for 30 seconds. How much charge is transferred?

V =IR12 = 0.5 R24 Ω = R

Page 20: Chapter 19 Review Current and Resistance. 1. A current of 2 amps flows for 30 seconds. How much charge is transferred?

10. What four factors affect the resistance of a conducting wire and what effect do they have?

Page 21: Chapter 19 Review Current and Resistance. 1. A current of 2 amps flows for 30 seconds. How much charge is transferred?

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

Page 22: Chapter 19 Review Current and Resistance. 1. A current of 2 amps flows for 30 seconds. How much charge is transferred?

11. What is a superconductor? What is critical temperature?

Page 23: Chapter 19 Review Current and Resistance. 1. A current of 2 amps flows for 30 seconds. How much charge is transferred?

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.)

Page 24: Chapter 19 Review Current and Resistance. 1. A current of 2 amps flows for 30 seconds. How much charge is transferred?

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?

Page 25: Chapter 19 Review Current and Resistance. 1. A current of 2 amps flows for 30 seconds. How much charge is transferred?

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.

Page 26: Chapter 19 Review Current and Resistance. 1. A current of 2 amps flows for 30 seconds. How much charge is transferred?

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?

Page 27: Chapter 19 Review Current and Resistance. 1. A current of 2 amps flows for 30 seconds. How much charge is transferred?

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!

Page 28: Chapter 19 Review Current and Resistance. 1. A current of 2 amps flows for 30 seconds. How much charge is transferred?

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?

Page 29: Chapter 19 Review Current and Resistance. 1. A current of 2 amps flows for 30 seconds. How much charge is transferred?

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!

Page 30: Chapter 19 Review Current and Resistance. 1. A current of 2 amps flows for 30 seconds. How much charge is transferred?

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?

Page 31: Chapter 19 Review Current and Resistance. 1. A current of 2 amps flows for 30 seconds. How much charge is transferred?

P = IVP = 15 x 120P = 1800 W

Page 32: Chapter 19 Review Current and Resistance. 1. A current of 2 amps flows for 30 seconds. How much charge is transferred?

16. If a resistance of 240 Ω is in a 120 V circuit, what is the power output of the resistance?

Page 33: Chapter 19 Review Current and Resistance. 1. A current of 2 amps flows for 30 seconds. How much charge is transferred?

V = IR120 = I(240)I = 0.5 AP = IVP = 0.5 x 120P = 60 W

Page 34: Chapter 19 Review Current and Resistance. 1. A current of 2 amps flows for 30 seconds. How much charge is transferred?

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?

Page 35: Chapter 19 Review Current and Resistance. 1. A current of 2 amps flows for 30 seconds. How much charge is transferred?

P = IV1500 = I(110)I = 13.6 AV = IR110 = 13.6 R8.1 Ω = R

Page 36: Chapter 19 Review Current and Resistance. 1. A current of 2 amps flows for 30 seconds. How much charge is transferred?

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?

Page 37: Chapter 19 Review Current and Resistance. 1. A current of 2 amps flows for 30 seconds. How much charge is transferred?

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

Page 38: Chapter 19 Review Current and Resistance. 1. A current of 2 amps flows for 30 seconds. How much charge is transferred?

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?

Page 39: Chapter 19 Review Current and Resistance. 1. A current of 2 amps flows for 30 seconds. How much charge is transferred?

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

Page 40: Chapter 19 Review Current and Resistance. 1. A current of 2 amps flows for 30 seconds. How much charge is transferred?