Multiple Choice Identify the letter of the choice that best completes the statement or answers the question.

Transcription

1 Electrical Circuits Multiple Choice Identify the letter of the choice that best completes the statement or answers the question. 1. In solid conductors, electric current is the flow of a. positive and negative charges. b. electrons. c. negative ions. d. protons. 2. Electrons move in an electric circuit a. by being bumped by other electrons. b. by interacting with an established electric field. c. by colliding with molecules. d. because the wires are so thin. 3. An ampere is a a. unit of resistance. b. unit of current. c. type of charge. d. voltage. e. current. 4. 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 5. Electrical resistance in a wire depends on the wire's a. thickness. b. conductivity. c. length. d. all of the above 6. Compared to thin wires, electrical resistance in thick wires is a. less. b. the same. c. greater. 7. For most conductors, as their temperature increases, their resistance a. decreases. b. increases. c. stays the same. 8. Electrical resistance is measured in a. volts. b. joules. c. watts. d. amperes.

2 9. A woman experiences an electric shock. The electrons making the shock come from a. the ground. b. the electric field in the air. c. a nearby power supply. d. the woman's body. e. the object causing the shock. 10. A pulsating electric field can travel through a wire at a speed of a. less than 1 cm/s. b. about 100 cm/s. c. the speed of sound waves in metal. d. nearly the speed of light. 11. A wire carrying a current is normally charged a. not at all. b. positively. c. negatively. 12. The primary reason a bird can perch harmlessly on bare high voltage wires is that a. a bird's feet are close together. b. a bird has a very large electrical resistance. c. there is no potential difference across the bird's feet. d. all of the above 13. Alternating current is made by a. alternating current and voltage. b. alternating the direction of voltage of the power source. c. huge chemical batteries. d. none of the above 14. The frequency of AC current in North America is a. 120 V. b. 50 hertz. c. 30 V. d. 60 hertz. 15. Current from a battery is always a. DC. b. AC. 16. The net speed of electrons in a wire is about a cm/s. b. 10 m/s. c. 100 kilometers per hour. d. a few million kilometers per hour. e. the speed of light. 17. Where do the electrons come from that produce heat and light in a light bulb? a. the power company b. the air c. the wall plug d. the bulb's wire filament 18. In 2004, the number of electrons delivered to an average American home by an average power utility was a. zero. b c. 220.

3 d. billions of billions. 19. When we say an appliance uses up electricity, we really are saying that a. electrons are taken out of the circuit and put somewhere else. b. electron kinetic energy is changed into heat and other forms of energy. c. the main power supply voltage is lowered. d. current disappears. e. electric charges are dissipated. 20. If you plug an electric toaster rated at 110 V into a 220-V outlet, current in the toaster will be a. twice what it should be. b. the same as if it were plugged into 110 V. c. half what it should be. d. more than twice what it should be. 21. Electric power is defined as a. current times voltage. b. current divided by voltage. c. current times resistance. d. resistance times voltage. e. voltage divided by current. 22. Power outlets in our homes typically have a potential difference of a. 30 V. b. 120 A. c. 60 A. d. 240 V. e. 120 V. 23. When an 8-V battery is connected to a resistor, 2 A of current flows in the resistor. What is the resistor's value? a. 2 ohms b. 4 ohms c. 8 ohms d. 16 ohms e. more than 16 ohms 24. The current through a 5-ohm resistor connected to a 150-V power supply is a. 1A. b. 10 A. c. 30 A. d. 150 A. 25. A 15-ohm resistor has a 5-A current in it. What is the voltage across the resistor? a. 5 V b. 15 V c. 20 V d. 25 V e. more than 25 V 26. What is the resistance of a toaster that uses 5 A of current when connected to a 120-volt power source? a. 5 ohms b. 24 ohms c. 120 ohms

4 d. 600 ohms 27. When connected to a 110-volt power supply, how much current is in a light bulb that has a resistance of 220 ohms? a. 0.5 A b. 2.0 A c. 110 A d. 220 A e. 24,200 A 28. If you accidentally grabbed the prongs of a partially plugged-in 120-V electrical plug on a day when your skin resistance was 130,000 ohms, how much current would pass through your body? a A b. 120 A c. 1,083 A d. 130,000 A e. 15,600,000 A 29. Electrical resistance is measured in a. volts. b. amperes. c. joules. d. watts A closed circuit is a circuit in which charge a. can flow. b. is prevented from flowing. 31. 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. 32. 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. 33. When resistors are put in parallel with each other their overall resistance is a. smaller than the resistance of any of the resistors. b. larger than the resistance of any other resistor. c. the same as the resistance of one of the resistors. 34. As more lamps are put into a series circuit, the overall current in the circuit a. stays the same. b. increases. c. decreases. 35. As more lamps are put into a parallel circuit, the overall current in the circuit a. increases. b. stays the same. c. decreases. 36. Compared to the resistance of two resistors connected in series, the same two resistors connected in parallel have

5 a. less resistance. b. more resistance. c. the same resistance. 37. When one light bulb in a series circuit containing several light bulbs burns out a. none of the other bulbs will light up. b. nothing changes in the rest of the circuit. c. the other light bulbs burn brighter. 38. 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. 39. In a simple parallel circuit a. current through each branch is always the same. b. voltage across each branch is always the same. c. the value of each resistor is the same. d. the circuit won't work unless there is a fuse in it. 40. Electrical devices in our homes are connected in a. parallel. b. series. 41. Fuses and circuit breakers are used to a. protect us. b. prevent overloading. c. keep wires from getting overheated. d. break the circuit when too much current is being used. e. all of the above 42. In order for current to flow in a circuit, you must have a. a switch that is open. b. a complete path for the current. c. two light bulbs in parallel. d. two light bulbs in series. e. all of the above 43. When two light bulbs are connected in series, the a. current through each light bulb is proportional to the resistance of the bulb. b. same amount of current always flows through each bulb. c. neither A nor B Essay 44. What is electrical resistance? What characteristics of a wire determine its resistance? How does resistance normally vary with temperature? 45. What is the difference between direct current and alternating current? When we plug a light bulb into a wall outlet, where do the electrons come from?

6 Electrical Circuits Answer Section MULTIPLE CHOICE 1. ANS: B DIF: 1 REF: p. 532 OBJ: 34.2, Ph.5.e 2. ANS: B DIF: 2 REF: p. 541 OBJ: ANS: B DIF: 1 REF: p. 533 OBJ: 34.2, Ph.5.e 4. ANS: E DIF: 2 REF: p. 533 OBJ: ANS: D DIF: 2 REF: p. 534 OBJ: ANS: A DIF: 2 REF: p. 534 OBJ: ANS: B DIF: 2 REF: p. 534 OBJ: ANS: E DIF: 1 REF: p. 534 OBJ: ANS: D DIF: 2 REF: p. 543 OBJ: ANS: C DIF: 1 REF: p. 542 OBJ: ANS: A DIF: 2 REF: p. 541 OBJ: ANS: C DIF: 2 REF: p. 538 OBJ: 34.6 STO: Ph.5.m 13. ANS: B DIF: 2 REF: p. 539 OBJ: ANS: D DIF: 1 REF: p. 539 OBJ: ANS: A DIF: 1 REF: p. 539 OBJ: ANS: A DIF: 1 REF: p. 541 OBJ: ANS: D DIF: 3 REF: p. 543 OBJ: ANS: A DIF: 3 REF: p. 543 OBJ: ANS: B DIF: 2 REF: p. 543 OBJ: ANS: A DIF: 2 REF: p. 535 OBJ: ANS: A DIF: 1 REF: p. 543 OBJ: 34.11, Ph.5.b, Ph.5.c 22. ANS: E DIF: 1 REF: p. 539 OBJ: 34.7

7 23. ANS: B DIF: 2 REF: p. 535 OBJ: ANS: C DIF: 2 REF: p. 535 OBJ: ANS: E DIF: 2 REF: p. 535 OBJ: ANS: B DIF: 2 REF: p. 535 OBJ: ANS: A DIF: 2 REF: p. 535 OBJ: ANS: A DIF: 2 REF: p. 535, p. 537 OBJ: 34.5, 34.6, Ph.5.m 29. ANS: E DIF: 1 REF: p. 555 OBJ: ANS: A DIF: 1 REF: p. 549 OBJ: ANS: D DIF: 1 REF: p. 554 OBJ: ANS: B DIF: 2 REF: p. 551 OBJ: ANS: A DIF: 2 REF: p. 552 OBJ: ANS: C DIF: 2 REF: p. 551 OBJ: ANS: A DIF: 2 REF: p. 552 OBJ: ANS: A DIF: 2 REF: p. 551 OBJ: ANS: A DIF: 2 REF: p. 550 OBJ: ANS: C DIF: 2 REF: p. 552 OBJ: ANS: B DIF: 2 REF: p. 552 OBJ: ANS: A DIF: 2 REF: p. 558 OBJ: ANS: E DIF: 1 REF: p. 558 OBJ: ANS: B DIF: 2 REF: p. 549 OBJ: ANS: B DIF: 2 REF: p. 550, p. 551 OBJ: 35.3 ESSAY 44. ANS:

8 Electrical resistance is the resistance a conductor offers to the general movement of electrons. Resistance of a wire depends on what material the wire is made of as well as the dimensions of the wire. Resistance increases with temperature. DIF: 3 REF: p. 534, p. 535 OBJ: ANS: In a direct-current circuit the polarity of the source never changes, whereas in an alternating-current circuit the source polarity changes at a fixed rate, typically 60 times per second. When we plug a light bulb into the wall outlet, the electrons that actually cause light and heat to be emitted are already in the bulb itself. The power company supplies energy; we supply the electrons! DIF: 3 REF: p. 539, p. 539 OBJ: 34.7