# Chapter 18 Electric Current and Circuits ```Chapter 18 Electric Current and Circuits
3. When a current flows down a wire:
A. electrons are moving in the direction of the current.
B. electrons are moving opposite the direction of the current.
C. protons are moving in the direction of the current.
D. protons are moving opposite the direction of the current.
E. both protons and electrons are moving in the direction of the current.
4. In a liquid, a current is set up between points A and B. Positive ions are going from A to B moving 6.0
coulombs of positive charge per second and negative charges are moving from B to A moving 2.0 coulombs of
negative charge per second. What is the current from A to B?
A. 8.0 A
B. -8.0 A
C. 4.0 A
D. -4.0 A
E. 12 A
6. A 2.50 A current is carried by a copper wire of radius 1.0 mm. If the density of conduction electrons is 8.0 &times;
1028/m3, what is the drift velocity of the conduction electrons?
A. 3.0 &times; 10-8 m/s
B. 3.2 &times; 10 -4 m/s
C. 1.6 &times; 10 -5 m/s
D. 6.2 &times; 10 -4 m/s
E. 6.2 x10 -5 m/s
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7. Two copper wires, one double the diameter of the other, have the same current flowing through them. If the
thinner wire has a drift velocity v1, and the thicker wire has a drift velocity v2, how do the drift velocities of the
charge carriers compare?
A. v1 = v2
B. v1 = 2 v2
C. 2 v1 = v2
D. v1 = 4 v2
E. 4 v1 = v2
13. A length L0 of wire has a resistance of 32.0 Ω. The wire is uniformly stretched to four times its original
length, i.e., 4 L0. If a length L0 is now cut from the stretched wire, what is its resistance?
A. 512 Ω
B. 128 Ω
C. 32.0 Ω
D. 8.00 Ω
E. 2.00 Ω
15. The resistance of a wire increases 3.9% when the temperature of the wire is raised 100&deg;C. What is the
temperature coefficient of resistivity of the wire material?
A. 3.9&deg;C-1
B. 0.39&deg;C-1
C. 0.039&deg;C-1
D. 0.0039&deg;C-1
E. 0.00039&deg;C-1
16. A resistor has a resistance of 30 Ω at 20&deg;C . If the temperature coefficient is 4.5 &times; 10-3&deg;C-1, what is its
resistance at 200&deg;C?
A. 24 Ω
B. 27 Ω
C. 48 Ω
D. 54 Ω
E. 57 Ω
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17. A 1.56-V battery has an internal resistance of 0.120 Ω. What is the maximum current that can be drawn
from this battery?
A. infinite (or at least 1000's of amps)
B. 1.56 A
C. 0.190 A
D. 13.0 A
E. 7.50 A
18. A potential difference of 12.4 V is placed across a 4.1 Ω resistor. What is the current in the resistor?
A. 51 A
B. 3.0 A
C. 0.33 A
D. 16A
E. 8.3 A
20. A variable resistor has a voltage of 12.0 V placed across it. If the resistance is increased 20%, what happens
to the current through it?
A. It increases 20%.
B. It increases 25%.
C. It decreases 20%.
D. It decreases 25%.
E. It decreases 17%.
21. A 12.0 V battery is placed across a 4.00 Ω resistor. If the current through the resistor is 2.80 A, what is the
internal resistance of the battery?
A. 0.200 Ω
B. 0.290 Ω
C. 4.29 Ω
D. 3.71 Ω
E. 0.800 Ω
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25. The potential differences around a loop ABCA in a circuit (starting at A and going back to A. are VAB = 10
V, VBC = 6.0 V, and VCA. What is VCA?
A. 16 V
B. 4.0 V
C. -4.0 V
D. -16 V
E. -12 V
28. Four 12 Ω resistors are connected together. Which of the following resistances cannot be formed using all 4
resistors?
A. 48 Ω
B. 9.0 Ω
C. 12 Ω
D. 60 Ω
E. 20 Ω
31. What is the resistance of the combination of resistors?
A. 4.0 Ω
B. 12 Ω
C. 13 Ω
D. 14 Ω
E. 15 Ω
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33. Capacitors of values 6.00 mF and 9.00 mF are connected in series to a 30.0 V power supply. What is the
resulting charge on the 6.00 mF capacitor?
A. 180 mC
B. 270 mC
C. 90.0 mC
D. 108 mC
E. 200 mC
34. Capacitors of values 6.0 mF and 9.0 mF are connected in series to a 30.0 V power supply. What is the
resulting potential difference across the 6.0 mF capacitor?
A. 30 V
B. 18 V
C. 12 V
D. 6.0 V
E. 3.0 V
35. Capacitors of values 1.0 F, 2.0 F, 3.0 F, and 6.0 F are connected in series across a 12 V power supply.
Which capacitor has the greatest potential difference across it?
A. The 1.0 F capacitor
B. The 2.0 F capacitor
C. The 3.0 F capacitor
D. The 6.0 F capacitor
E. They all are equal.
36. Capacitors of values 1.0 F, 2.0 F, 3.0 F, and 6.0 F are connected in series across a 12 V power supply.
Which capacitor has the greatest charge on it?
A. The 1.0 F capacitor.
B. The 2.0 F capacitor.
C. The 3.0 F capacitor.
D. The 6.0 F capacitor.
E. They are all equal.
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37. The arrangement is composed of four 6.0 mF capacitors. What is the capacitance of the combination?
A. 24.0 mF
B. 4.5 mF
C. 8.0 mF
D. 9.0 mF
E. 12.5 mF
38. In the diagram, each resistor is 3 ohms and the battery is 9 volts. What is the current through the middle
resistor?
A. 3 A to the right
B. 3 A to the left
C. 9 A to the right
D. 9 A to the left
E. 1 A to the left
39. Three resistors, R1 = 4 Ω, R2 = 3.0 Ω, and R3 = 2.0 Ω, are connected in series to a 9.0 V battery. What is the
power dissipated by R1?
A. 2.0 W
B. 4.0 W
C. 5.1 W
D. 9.0 W
E. 2.3 W
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40. In the diagram, if the current through R1 is 5 A up and if the current through R3 is 3 A up, what is the
current in R2?
A. 8 A up
B. 8 A down
C. 2 A up
D. 2 A down
42. If R1 = 6.0 Ω, R2 = 8.0 Ω, R3 = 2.0 Ω, ε1 = 4.0 V, and ε2 = 14 V, what is the power supplied to the circuit by
ε1?
A. 4.0 W
B. 8.0 W
C. 12 W
D. 16 W
E. 20 W
46. Raising the current through a resistor from 8.50 A to 11.3 A increases the power by:
A. 33.0%.
B. 77.0%.
C. 113%.
D. 157%.
E. 0% (no change).
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51. A flashlight, which uses two 1.5 V batteries in series, is turned on for 2.0 minutes. If the current in the
flashlight is 100 mA, what is the energy dissipated?
A. 12 J
B. 9.0 J
C. 72 J
D. 36 J
E. 18 J
53. A 2.0 Ω resistor is connected across a 6.0 V power supply. An ammeter with internal resistance of 1.0 Ω is
used to measure the current in this circuit. What is the ammeter reading?
A. 4.0 A
B. 3.0 A
C. 2.0 A
D. 1.0 A
E. An ammeter with less resistance than the rest of the circuit will not produce a reading.
54. A 1000 Ω resistor is in a circuit with 30.0 mA flowing through it. A voltmeter with internal resistance 1000
Ω is used to measure the voltage across the resistor. What is the reading from the voltmeter if 30.0 mA still
flows in the circuit?
A. 30.0 V
B. 29.9 V
C. 27.0 V
D. 15.0 V
E. 3.00 V
55. A series circuit consists of a 12.0 V source of emf, a 2.00 mF capacitor, a 1000 Ω resistor, and a switch.
What is the time constant for this circuit?
A. 10.0 s
B. 2.00 s
C. 0.693 s
D. 0.0825 s
E. 1.00 ms
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56. A series circuit consists of a 1.02 V source of emf, a 2.00 mF capacitor, a 1000 Ω resistor, and a switch.
When the switch is closed, how long does it take for the current to reach one-half its maximum value?
A. 0.693 s
B. 1.39 s
C. 2.00 s
D. 1.69 s
E. 0.0250 s
59. A capacitor is connected in series with a resistor and a switch. With the switch open, the capacitor is
charged to 9.0 V. When the switch is closed, how long will it take for the voltage across the capacitor to drop to
6.0 V if the time constant of the circuit is 4.0 s?
A. 0.3 s
B. 1.2 s
C. 1.6 s
D. 2.7 s
E. 12 s
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