Class: Date: Exam 2 Multiple Choice Identify the choice that best completes the statement or answers the question. 1. You wish to measure a current through a resistor. You should connect the measuring device in what way? a. in series with the resistor c. replace the resistor with the measuring device b. in parallel with the resistor d. it depends on the circuit 2. A current of 20 A flows through a wire of length 1 m and diameter 1 mm. The potential across the wire is 1.4 V. From this table of resistivities, select the material of the wire: Material Resistivity(Ohm-m) Copper 1.7x10-8 Silver 1.59x10-8 Gold 2.44x10-8 Tungsten 5.5x10-8 Iron 10.0x10-8 a. Copper d. Tungsten b. Silver e. Iron c. Gold 3. A 3 V potential difference is maintained across a 10 Ω resistor for 2 minutes. How many electrons pass through the material? a. 2.25x10 20 d. 0.3 b. 60 e. 36 c. 3.75x10 18 4. Nonohmic materials a. all of the above c. do not obey Ohm s Law b. do not include most resistors d. include diodes 5. A one-hundred watt lightbulb and a 50-watt lightbulb are in parallel with a power supply of 100 V. What current flows through the 100 W light bulb? a. 1/2 A c. None of the above b. 2 A d. 1 A 6. A 50Ω and a 100Ω resistor are in series with a power supply of 150 V. What amount of energy is dissipated across the 50Ω resistor in 3 seconds? a. 300 J c. 450 J b. 100 J d. 150 J 1
7. The electric company charges a rate of $0.10 per kilowatt-hour. How much does it cost to run a 100 W bulb for 10 hours? a. $1 c. $0.36 b. $10 d. $0.10 8. On a circuit breaker, you have a 1200 W heater, a 60 W light bulb, and a 240 W radio. When you add a 180 W blender, the circuit breaker turns off. Assume all the devices operate at 120 V. Which of these is the maximum allowed current for the breaker? a. 20 A c. 10 A b. 13 A d. 15 A 9. Two wires, A and B, are made of the same metal and have equal length, but the resistance of wire A is 16 times the resistance of wire B. How do their diameters compare? a. d A =d B d. d A =4d B b. d A =2d B e. d A = 1 2 d B c. d A = 1 4 d B 10. When you rotate the knob of a light dimmer, what is being changed in the electric circuit? a. resistance d. just power & current b. current e. all of the above c. power 11. In your house, two lightbulbs operate at 120 V, but one has a power rating of 25 W while the other has a power rating of 100 W. Which one has the greater current flowing through it? a. 25 W bulb c. both have same current b. not enough information d. 100 W bulb 12. Two space heaters in your living room are operated at 120 V. Heater 1 has twice the resistance of heater 2. Which one will give off more heat? a. Heater 1 c. both will give same heat b. Heater 2 d. not enough information 2
13. A battery has an internal resistance of 1Ω. When it provides a current of 2 A, the potential across the battery is 10 V. What is the ideal electromotive force provided by the battery? a. 5 V c. 30 V b. 12 V d. 20 V 14. What is the equivalent resistance of this circuit? a. 5.6 Ω c. 5.1 Ω b. 25 Ω d. 4.1 Ω 15. Two resistors of 7Ω and 3Ω are in series with a 10 V battery. What is the current through the 3Ω resistor? a. 3.33 A c. 1.4 A b. 1 A d. 0.3 A 3
16. Three resistors of 2Ω, 4Ω, and 4Ω are in parallel with a power supply of 10 V. What is the total current through the circuit? a. 2.5 A c. 10 A b. 5 A d. 1 A 17. The ammeter in this circuit reads a current of I 3 =1 A. What is the current I 1? a. 1.1 A c. 1.4 A b. 1.25 A d. 2.9 A 4
18. Which of these equations is appropriate (ie. correct) for this circuit? a. 10-6I 2-2I 3 =0 d. 14+6I 1-10-4I 2 =0 b. I 1 +I 3 =I 2 e. 14-4I 2 +2I 3 =0 c. 2I 3 +6I 1-10=0 5
19. In this circuit, what happens to the current in each resistor as you add resistors in parallel? a. Current decreases c. It depends on the value of the added resistance b. Current stays the same d. Current increases 20. In this circuit, what happens to the brightness of bulb A when you close the switch? a. not enough information c. glows just the same as before b. glows brighter than before d. glows less than before 6
21. In this figure, light bulbs A, B, and C each have a resistance of 1Ω. How do the brightness of bulbs A and C compare? a. bulb A is four times as bright as C d. bulb A is the same brightness as C b. bulb A is twice as bright as C e. bulb A is 1/4 as bright as C c. bulb A is 1/2 as bright as C 22. When 2 or more resistors are connected in parallel to a battery, a. all of the above c. the equivalent resistance of the combination is less than or equal to the resistance of any one of the resistors b. the voltage across each resistor is the same d. the total current flowing from the battery equals the sum of the currents flowing through each resistor 23. Three identical resistors are connected in series to an ideal battery with V=12 V. What is the potential across each resistor? a. 4 V c. 3 V b. 2 V d. 6 V 7
24. In this RC circuit, the time constant is 1 µs and the resistance is 10 Ω. What is the capacitance, C? a. 2 µf d. 1 µf b. 0.1 µc e. 0.1 µf c. 10 µf 25. What happens to the voltage across the resistor R 1 when the switch is closed? The voltage will: a. decrease c. stay the same b. increase d. not enough information given 8
26. What happens to the current through the resistor R 1 when the switch S is closed? R 1 V S R 2 R 3 R 4 a. decreases c. stays the same b. increases 27. Assume each of these resistances are identical. Which resistor(s) has the least amount of current flowing through it? V R 3 R 4 R 2 R 5 R 1 R 2 a. R 5 d. R 1 b. both R 3 and R 4 equally e. all the same c. both R 1 and R 2 equally 28. What purpose does the third prong on a three-prong outlet serve? a. Allow for more stability in the outlet c. Act as a ground thus providing a safety feature b. An alternative to the European system of electrical outlets d. No purpose 29. GFCI stands for a. Gauge for Circuit Integrity c. Good For Cashing In b. Ground Force Circuit Interpreter d. Ground Fault Circuit Interrupt 30. A household circuit has all of the electrical devices connected in _. a. it depends on the house c. series b. parallel d. a combination of series and parallel 31. The correct answer to this question is A. Please write A above your name on the scantron. a. A c. C b. B d. D 9
Exam 2 Answer Section MULTIPLE CHOICE 1. ANS: A PTS: 1 2. ANS: D PTS: 1 3. ANS: A PTS: 1 4. ANS: A PTS: 1 5. ANS: D PTS: 1 6. ANS: D PTS: 1 7. ANS: D PTS: 1 8. ANS: B PTS: 1 9. ANS: C PTS: 1 10. ANS: E PTS: 1 11. ANS: D PTS: 1 12. ANS: B PTS: 1 13. ANS: B PTS: 1 14. ANS: C PTS: 1 15. ANS: B PTS: 1 16. ANS: C PTS: 1 17. ANS: C PTS: 1 18. ANS: C PTS: 1 19. ANS: B PTS: 1 20. ANS: B PTS: 1 21. ANS: A PTS: 1 22. ANS: A PTS: 1 23. ANS: A PTS: 1 24. ANS: E PTS: 1 25. ANS: B PTS: 1 26. ANS: B PTS: 1 27. ANS: B PTS: 1 28. ANS: C PTS: 1 29. ANS: D PTS: 1 30. ANS: B PTS: 1 31. ANS: A PTS: 1 1