Name: Class: Date: Exam 2 Multiple Choice Identify the choice that best completes the statement or answers the question. 1. For this circuit, which of these equations is correct? a. 80-1I 2-20I 2-30I 1 =0 c. 45-1I 2-40I 3-30I 1 =0 b. I 1 +I 3 =I 2 d. -30I 1 +20I 2 +1I 2-80=0 2. A current of 20 A flows through a wire of length 1 m and diameter 1 mm. The potential across the wire is 0.32 V. From this table of resistivities, select the material of the wire: Material Resistivity(Ohm-m) Copper 1.7x10-8 Silver 1.26x10-8 Gold 2.44x10-8 Tungsten 5.5x10-8 Iron 10.0x10-8 a. Copper d. Tungsten b. Silver e. Iron c. Gold 1
Name: 3. What is the potential across the 8Ω resistor? a. 2 V c. 4 V b. 6 V d. 16 V 4. In a single circuit within your house, what happens to the total current as you add electrical appliances? a. the current stays the same c. the current decreases b. the current increases d. none of these 5. You wish to measure a voltage across a resistor. You should connect the measuring device in what way? a. in parallel with the resistor c. in series with the resistor b. replace the resistor with the measuring d. it depends on the circuit device 6. The GFCI measures which of these? a. Voltage c. Current b. Potential d. Power 7. A 2.0 V potential difference is maintained across a 10. Ω resistor for a period of 2.0 minutes. What total charge passes through the resistor in this time? a. 40 C c. 0.40 C b. 24 C d. 10. C 2
Name: 8. What is the required resistance of your hot water heater element if you are to heat 25 kg of water from 0 C to 20 C in 30 minutes. Assume the heater operates at 220 V. (The specific heat of water is 4186 J/kg C) a. 40 Ω c. 420 Ω b. 3 Ω d. 10,000 Ω 9. If the ammeter in this circuit reads a current of I 3 =2 A. What is the current I 1? a. 1.4 A c. 0.4 A b. 0.7 A d. 1.25 A 3
Name: 10. An RC circuit has a resistance of 3 MΩ in series with a capacitor of 2 µf. After 25 seconds, has the capacitor fully charged? a. No c. Not enough information b. Yes 11. When you rotate the knob of a light dimmer, what is being changed: I. Resistance II. Potential III. Current IV. Power a. III and IV c. I, III, and IV b. II only d. II and III 12. When 2 or more resistors are connected in parallel to a battery, a. all of the above c. the total current flowing from the battery equals the sum of the currents flowing through each resistor b. the equivalent resistance of the combination is less than or equal to the resistance of any one of the resistors d. the voltage across each resistor is the same 13. A heater with a resistance of 5 Ω is connected to a potential of 100V. How much energy is output in 20 seconds? a. 10,000 J c. 20,000 J b. 40,000 J d. 25 J 4
Name: 14. In this circuit, how much brighter or dimmer is bulb A compared with bulb C? Assume the bulbs have the same resistance. A B C 10 V a. A is 4 times as bright as C d. A is twice as bright as C b. A is 1/4 as bright as C e. A has the same brightness as C c. A is 1/2 as bright as C 15. In this RC circuit, the time constant is 1 s and the resistance is 10 MΩ. What is the capacitance, C? a. 1 µf d. 0.1 µf b. 10 µf e. 2 µf c. 0.1 µc 5
Name: 16. Two identical light bulbs are connected either in series or parallel to identical batteries. Which circuit gives the most light? 17. a. the parallel circtuit c. the series circuit b. they are both the same d. not enough information In this circuit, if I 1 =2 A and I 3 =4 A, what is I 2? a. 2 A c. 8 A b. 6 A d. none of these 6
Name: 18. What is the current in this circuit? a. 3.1 A c. 0.63 A b. 2.0 A d. 0.32 A 19. When you apply a potential of 3 V to a particular electrical device, the current in 1 A. When you apply 6V, the current is 2 A. Is this device Ohmic or Non-Ohmic? a. Ohmic c. Neither b. Non-Ohmic d. Not enough information 20. Two lightbulbs operate at 120 volts. One is brighter than the other. Which has the higher resistance? a. they have the same resistance c. the dimmer one b. the brighter one d. not enough information 21. The third prong on electrical outlets provides what: a. an emergency switch c. a current measuring device b. more stability for the electrical plug d. an alternate ground 7
Name: 22. If the switch S is closed, what happens to the potential across R 2? a. decreases c. stays the same b. increases d. not enough information 23. Two wires, A and B, have the same physical dimensions. The resistance of wire A is 1/2 that of wire B. How do their resistivities compare? a. ρ A =2 ρ B c. ρ A = ρ B b. ρ A =4 ρ B d. ρ A = ρ B 24. What does GFCI an abbreviation for? a. Great Food Comes Interspersed c. Ground Fault Current Instrument b. Ground Fault Circuit Interrupt d. Ground safety Circuit Instrument 25. On a circuit breaker, you have a 1200 W heater and a 720 W fan. When you add a 240 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. 17 A c. 13 A b. 19 A d. 8 A 26. 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. $0.36 c. $1 b. $0.10 d. $10 8
Name: 27. What is the equivalent resistance of this circuit? a. 0.8 Ω c. 8 Ω b. 5 Ω d. 4 Ω 28. The answer to this question is B a. A c. C b. B d. D 9
Exam 2 Answer Section MULTIPLE CHOICE 1. ANS: D PTS: 1 2. ANS: B PTS: 1 3. ANS: C PTS: 1 4. ANS: B PTS: 1 5. ANS: A PTS: 1 6. ANS: C PTS: 1 7. ANS: B PTS: 1 8. ANS: A PTS: 1 9. ANS: B PTS: 1 10. ANS: A PTS: 1 11. ANS: C PTS: 1 12. ANS: A PTS: 1 13. ANS: B PTS: 1 14. ANS: A PTS: 1 15. ANS: C PTS: 1 16. ANS: A PTS: 1 17. ANS: A PTS: 1 18. ANS: C PTS: 1 19. ANS: A PTS: 1 20. ANS: C PTS: 1 21. ANS: D PTS: 1 22. ANS: A PTS: 1 23. ANS: C PTS: 1 24. ANS: B PTS: 1 25. ANS: A PTS: 1 26. ANS: B PTS: 1 27. ANS: B PTS: 1 28. ANS: B PTS: 1 1