Chapter 23

1. Chapter 23 Electric Current

2. The flow of charge in an electric circuit is much • like the flow of water in a system of pipes. • different than water flow in pipes. • like an electric valve. • like an electric pump.

3. The flow of charge in an electric circuit is much • like the flow of water in a system of pipes. • different than water flow in pipes. • like an electric valve. • like an electric pump.

4. Electric charge will flow in an electric circuit when • electrical resistance is low enough. • a potential difference exists. • the circuit is grounded. • electrical devices in the circuit are not defective.

5. Electric charge will flow in an electric circuit when • electrical resistance is low enough. • a potential difference exists. • the circuit is grounded. • electrical devices in the circuit are not defective.

6. The electric current in a copper wire is normally composed of • electrons. • protons. • ions. • All or any of these.

7. The electric current in a copper wire is normally composed of • electrons. • protons. • ions. • All or any of these. Explanation: Although current can consist of protons and ions, in a copper wire current consists of electrons appropriately called conduction electrons.

8. Which statement is correct? • Voltage flows in a circuit. • Charge flows in a circuit. • A battery is the source of electrons in a circuit. • All are correct.

9. Which statement is correct? • Voltage flows in a circuit. • Charge flows in a circuit. • A battery is the source of electrons in a circuit. • All are correct. Explanation: Voltage causes the flow of electrons, and doesn’t flow. Charges flow. A battery is a source of energy, not electrons.

10. Apply heat to a copper wire and the resistance of the wire • decreases. • remains unchanged. • increases. • vanishes with enough heat.

11. Apply heat to a copper wire and the resistance of the wire • decreases. • remains unchanged. • increases. • vanishes with enough heat.

12. The amount of current in a circuit depends on the • voltage across the circuit. • electrical resistance of the circuit. • Both of these. • None of these.

13. The amount of current in a circuit depends on the • voltage across the circuit. • electrical resistance of the circuit. • Both of these. • None of these.

14. When you double the voltage in a simple electric circuit, you double the • current. • resistance. • Both of these. • None of these.

15. When you double the voltage in a simple electric circuit, you double the • current. • resistance. • Both of these. • None of these. Explanation: This is straight-forward Ohm’s law. Current = voltage/resistance.

16. When 110 volts are impressed across a 22-ohm resistor, the current in the resistor is • 5 A. • 10 A. • 132 A. • 2420 A.

17. When 110 volts are impressed across a 22-ohm resistor, the current in the resistor is • 5 A. • 10 A. • 132 A. • 2420 A.

18. To receive an electric shock there must be • current in one direction. • moisture in the electrical device being used. • a difference in potential across part or all of the body. • high voltage and low body resistance.

19. To receive an electric shock there must be • current in one direction. • moisture in the electrical device being used. • a difference in potential across part or all of the body. • high voltage and low body resistance.

20. The difference between dc and ac in electrical circuits is that in dcthe electrons • flow steadily in one direction only. • flow in one direction only. • steadily flow to and fro. • flow to and fro.

21. The difference between dc and ac in electrical circuits is that in dc the electrons • flow steadily in one direction only. • flow in one direction only. • steadily flow to and fro. • flow to and fro.

22. Which device is used to convert ac to a fairly steady dc? • Diode • Capacitor • Both of these. • None of these.

23. Which device is used to convert ac to a fairly steady dc? • Diode • Capacitor • Both of these. • None of these. Explanation: Although a diode will convert ac to dc, the additional use of a capacitor produces steadiness (as Figure 23.11 in the text shows).

24. What travels at about the speed of light in an electric circuit? • Electric charges • Electric current • Electric field • All of these.

25. What travels at about the speed of light in an electric circuit? • Electric charges • Electric current • Electric field • All of these. Explanation: The electric field in a circuit travels at nearly the speed of light, not the electrons nor the current.

26. When you buy a water pipe in a hardware store, the water isn’t included. When you buy copper wire, electrons • must be supplied by you, just as water must be supplied for a water pipe. • are already in the wire. • may fall out, which is why wires are insulated. • None of these.

27. When you buy a water pipe in a hardware store, the water isn’t included. When you buy copper wire, electrons • must be supplied by you, just as water must be supplied for a water pipe. • are already in the wire. • may fall out, which is why wires are insulated. • None of these.

28. The drift speed of electrons that make up current in a circuit is • near the speed of light. • near the speed of sound. • about a snail’s pace. • imaginary.

29. The drift speed of electrons that make up current in a circuit is • near the speed of light. • near the speed of sound. • about a snail’s pace. • imaginary.

30. If you double both the current and the voltage in a circuit, the power • remains unchanged if resistance remains constant. • halves. • doubles. • quadruples.

31. If you double both the current and the voltage in a circuit, the power • remains unchanged if resistance remains constant. • halves. • doubles. • quadruples. Explanation: Electric power = current  voltage. Doubling both current and voltage corresponds to 4 times as much power.

32. A lamp with a current of 10 A connected to 120 volts consumes a power of • 10 W. • 12 W. • 120 W • 1200 W.

33. A lamp with a current of 10 A connected to 120 volts consumes a power of • 10 W. • 12 W. • 120 W • 1200 W.

34. Which of these lamps is the longer lasting in a common circuit? • Incandescent lamp • Compact fluorescent lamp • Light-emitting diode • All about the same.

35. Which of these lamps is the longer lasting in a common circuit? • Incandescent lamp • Compact fluorescent lamp • Light-emitting diode • All about the same. Comment: More about LEDs in Chapter 30.

36. In a simple circuit consisting of a single lamp and a single battery, when current in the lamp is 2 amperes, the current in the battery is • half, 1 A. • 2 A. • dependent on internal battery resistance. • Not enough information to say.

37. In a simple circuit consisting of a single lamp and a single battery, when current in the lamp is 2 amperes, the current in the battery is • half, 1 A. • 2 A. • dependent on internal battery resistance. • Not enough information to say. Comment: It is important to know that the current in the devices in series is also the current in the battery. Current will depend on battery resistance, but if there’s 2 A in the circuit, there’s 2 A in the battery!

38. In a circuit with two lamps in parallel, if the current in one lamp is 2 amperes, the current in the battery is • half, 1 A. • 2 A. • more than 2 A. • Not enough information to say.

39. In a circuit with two lamps in parallel, if the current in one lamp is 2 amperes, the current in the battery is • half, 1 A. • 2 A. • more than 2 A. • Not enough information to say. Explanation: Current in the battery will be the sum of currents in the two branches.

40. One way to prevent overloading in your home circuit is to • operate fewer devices at the same time. • change the wiring from parallel to series for troublesome devices. • find a way to bypass the fuse or circuit breaker. • All of these.

41. One way to prevent overloading in your home circuit is to • operate fewer devices at the same time. • change the wiring from parallel to series for troublesome devices. • find a way to bypass the fuse or circuit breaker. • All of these.