Deck 22: Current and Resistance

Question 1

If a quantity you calculated has units of , what is that quantity?

A) potential
B) resistivity
C) resistance
D) capacitance
E) charge

Answer 1

A

Question 2

The length of a certain wire is doubled while its radius is kept constant. What is the new resistance of this wire?

A) It stays the same.
B) It is 2 times as large.
C) It is 3 times as large.
D) It is 4 times as large.
E) It is 1/2 as large.

Answer 2

B

Question 3

The length of a certain wire is kept same while its radius is doubled. What is the new resistivity of this wire?

A) It is increased by a factor of 2.
B) It is increased by a factor of 4.
C) It is reduced by a factor of 2.
D) It is reduced by a factor of 4.
E) It does not change.

Answer 3

E

Question 4

You are given a copper bar of dimensions 3 cm × 5 cm × 8 cm and asked to attach leads to it in order to make a resistor. If you want to achieve the smallest possible resistance, you should attach the leads to the opposite faces that measure

A) 3 cm × 5 cm.
B) 3 cm × 8 cm.
C) 5 cm × 8 cm.
D) Any pair of faces produces the same resistance.

Question 5

A wire of resistivity ρ must be replaced in a circuit by a wire of the same material but four times as long. If, however, the total resistance is to remain as before, the diameter of the new wire must

A) be the same as the original diameter.
B) be one-half the original diameter.
C) be one-fourth the original diameter.
D) be two times the original diameter.
E) be four times the original diameter.

Question 6

When a current flows through an ionic liquid such as salty water, the moving charges are

A) only protons.
B) only electrons.
C) only negative ions.
D) only positive ions.
E) both positive and negative ions.

Question 7

When a current flows through a metal wire, the moving charges are

A) only protons.
B) only electrons.
C) both protons and electrons.
D) positive metal ions.
E) negative metal ions.

Question 8

The figure shows conventional current passing through a resistor. The arrow shows the direction in which this conventional current is flowing. Which of the following statements are correct? (There could be more than one correct choice.)

A) The charges are moving slower at point b than at point a.
B) The electric potential is lower at point b than at point a.
C) The electric potential is higher at point b than at point a.
D) The current at point b is the same as the current at point a.
E) The electric potential at point b is the same as it is at point a.

Question 9

For the graph shown in the figure, what physical quantity does the slope of the graph represent for ohmic material?

A) power
B) resistivity
C) 1/(resistivity)
D) resistance
E) 1/(resistance)

Question 10

Copper wire #1 has a length L and a radius b. Copper wire #2 has a length 2L and a radius 2b. Which statement about the resistance across the ends of the wires is true?

A) The resistance of wire #1 is twice as high as that of wire #2.
B) The resistance of wire #1 is equal to that of wire #2.
C) The resistance of wire #1 is half that of wire #2.
D) The resistance of wire #1 is four times higher than that of wire #2.

Question 11

The figure shows electrons passing through a resistor. The arrow shows the direction in which the electrons are moving. Which of the following statements are correct? (There could be more than one correct choice.)

A) The electrons are moving slower at point b than at point a.
B) The electric potential is higher at point b than at point a.
C) The electric potential is lower at point b than at point a.
D) The electrons are losing electric potential energy as they move through the resistor from a to b.
E) The speed of the electrons at point b is the same as it is at point a.

Question 12

The length of a certain wire is kept same while its radius is doubled. What is the new resistance of this wire?

A) It is increased by a factor of 2.
B) It is increased by a factor of 4.
C) It is reduced by a factor of 2.
D) It is reduced by a factor of 4.
E) It is reduced by a factor of 8.

Question 13

You are given a copper bar of dimensions 3 cm × 5 cm × 8 cm and asked to attach leads to it in order to make a resistor. If you want to achieve the largest possible resistance, you should attach the leads to the opposite faces that measure

A) 3 cm × 5 cm.
B) 3 cm × 8 cm.
C) 5 cm × 8 cm.
D) Any pair of faces produces the same resistance.

Question 14

For the graph shown in the figure, what physical quantity does the slope of the graph represent for ohmic material?

A) current
B) resistivity
C) 1/(current)
D) power
E) 1/(resistivity)

Question 15

If a quantity you calculated has units of Ω ∙ m what is that quantity?

A) potential
B) resistivity
C) resistance
D) capacitance
E) charge

Question 16

If a quantity you calculated has units of A ∙ s, what is that quantity?

A) potential
B) resistivity
C) resistance
D) capacitance
E) charge

Question 17

For the graph shown in the figure, what physical quantity does the slope of the graph represent for ohmic material?

A) power
B) resistivity
C) 1/(resistivity)
D) resistance
E) 1/(resistance)

Question 18

For the graph shown in the figure, what physical quantity does the slope of the graph represent for ohmic material?

A) current
B) resistivity
C) 1/(current)
D) power
E) 1/(resistivity)

Question 19

The figure shows a graph of the resistance of a wire as a function of its length. What physical quantities does the slope of this graph represent?

A) the cross-sectional area of the wire
B) the resistivity of the material of which the wire is made
C) the product of the resistivity and the cross-sectional area of the wire
D) the resistivity of the material divided by the cross-sectional area of the wire
E) the reciprocal of the resistivity of the material

Question 20

When current is flowing in an ordinary metal wire, the magnitude of the average velocity of the electrons is closest to

A) 10 m/s.
B) the speed of light.
C) 1 mm/s.
D) 1 km/s.
E) 1 m/s.

Question 21

If the current flowing through a circuit of constant resistance is doubled, the power dissipated by that circuit will

A) quadruple in magnitude.
B) double in magnitude.
C) decrease to one-half of what it was.
D) decrease to one-fourth of what it was.

Question 22

The length of a certain wire is doubled and at the same time its radius is also doubled. What is the new resistance of this wire?

A) It stays the same.
B) It is 2 times as large.
C) It is 4 times as large.
D) It is 1/2 as large.
E) It is 1/4 as large.

Question 23

For the graph shown in the figure, what physical quantity does the slope of the graph represent for a dc circuit?

A) resistivity
B) resistance
C) energy
D) current
E) capacitance

Question 24

Which one of the following quantities is equivalent to 1 Ω?

A) 1 J/s
B) 1 W/A
C) 1 V ∙ A
D) 1 V/A
E) 1 A ∙ s

Question 25

If the length and diameter of a wire of circular cross section are both tripled, the resistance will be

A) unchanged.
B) tripled.
C) increased by a factor of 9.
D) 1/3 of what it originally was.
E) 1/9 of what it originally was.

Question 26

If the resistance in a constant voltage circuit is doubled, the power dissipated by that circuit will

A) increase by a factor of two.
B) increase by a factor of four.
C) decrease to one-half its original value.
D) decrease to one-fourth its original value.

Question 27

A kilowatt-hour is equivalent to

A) 1000 W.
B) 3600 J.
C) 3,600,000 J/s.
D) 3,600,000 J.
E) 3600 J/s

Question 28

If a quantity you calculated has units of what is that quantity?

A) potential
B) resistivity
C) resistance
D) capacitance
E) current

Question 29

Which one of the following quantities is equivalent to 1 W?

A) 1 V/A
B) 1 Ω ∙ m
C) 1 V ∙ A
D) 1 V/Ω
E) 1 A ∙ s

Question 30

Consider two copper wires with circular cross-sections and equal lengths. One wire has 3 times the diameter of the other. How do the resistances of these two wires compare?

A) The thicker wire has 1/3 the resistance of the thinner wire.
B) The thicker wire has 1/9 the resistance of the thinner wire.
C) The thicker wire has 3 times the resistance of the thinner wire.
D) The thicker wire has 9 times the resistance of the thinner wire.
E) The thicker wire has times the resistance of the thinner wire.

Question 31

Consider two copper wires of equal cross-sectional area. One wire has 3 times the length of the other. How do the resistances of these two wires compare?

A) Both wires have the same resistance.
B) The longer wire has 1/3 the resistance of the shorter wire.
C) The longer wire has 3 times the resistance of the shorter wire.
D) The longer wire has 9 times times the resistance of the shorter wire.
E) The longer wire has 27 times times the resistance of the shorter wire.

Question 32

During a period of high power demand, the voltage output of the power company is reduced by 5.0%. By what percentage is the power in a resistor decreased?

A) 2.5%
B) 5.0%
C) 10%
D) 15%
E) 90%

Question 33

If the voltage across a circuit of constant resistance is doubled, the power dissipated by that circuit will

A) be four times as large.
B) be two times as large.
C) decrease to one-half the original power.
D) decrease to one-fourth the original power.

Question 34

If a quantity you calculated has units of what is that quantity?

A) potential
B) resistivity
C) resistance
D) capacitance
E) current

Question 35

The figure shows a graph of the power dissipated in a resistor as a function of the resistance. What quantity does the slope of this graph represent?

A) the current in the resistor
B) the potential difference across the resistor
C) the reciprocal of the current in the resistor
D) the square of the current in the resistor
E) the resistivity of the resistor

Question 36

If we double the resistance in a circuit but keep the current in it constant, the power dissipated by that circuit will

A) be four times as great.
B) be two times as great.
C) be one-half as great.
D) be one-fourth as great.

Question 37

Consider two copper wires of equal cross-sectional area. One wire has 3 times the length of the other. How do the resistivities of these two wires compare?

A) Both wires have the same resistivity.
B) The longer wire has 3 times the resistivity of the shorter wire.
C) The longer wire has 9 times times the resistivity of the shorter wire.
D) The longer wire has 27 times times the resistivity of the shorter wire.

Question 38

When the current through a resistor is increased by a factor of 4, the power dissipated by the resistor

A) decreases by a factor of 4.
B) decreases by a factor of 16.
C) increases by a factor of 16.
D) increases by a factor of 4.
E) increases by a factor of 2.

Question 39

Consider two copper wires of equal length. One wire has twice the cross-sectional area of the other. How do the resistances of these two wires compare?

A) The thicker wire has twice the resistance of the thinner wire.
B) The thicker wire has eight times the resistance of the thinner wire.
C) The thicker wire has one-half the resistance of the thinner wire.
D) The thicker wire has four times the resistance of the thinner wire.
E) The thicker wire has one-fourth the resistance of the thinner wire.

Question 40

The length of a certain wire is doubled and at the same time its radius is reduced by a factor of 2. What is the new resistance of this wire?

A) It is 2 times as large.
B) It is 4 times as large.
C) It is 6 times as large.
D) It it 8 times as large.
E) It is 1/2 as large.

Question 41

If a charge of 11.4 C passes through a computer in 1.75 min, what is the average current through the computer?

Question 42

What potential difference is required across an 8.0-Ω resistor to cause 2.0 A to flow through it?

Question 43

A 4000-Ω resistor is connected across a 220-V power source. What current will flow through the resistor?

A) 0.055 A
B) 1.8 A
C) 5.5 A
D) 18 A

Question 44

A total of 2.0 × 10¹³ electrons pass a given point in a wire in 15 s. What is the current in the wire? (e = 1.60 × 10^-19 C)

A) 1.3 mA
B) 1.3 A
C) 0.21 μA
D) 3.2 μA

Question 45

A electric heater that draws 13.5 A of dc current has been left on for 10 min. How many electrons that have passed through the heater during that time? (e = 1.60 × 10^-19 C)

A) 1.5 × 10²²
B) 5.1 × 10²²
C) 1.8 × 10³
D) 8.1 × 10³
E) 1.0 × 10²³

Question 46

How much charge must pass by a point in a wire in 10 s for the current inb the wire to be 0.50 A?

A) 20 C
B) 2.0 C
C) 5.0 C
D) 0.050 C

Question 47

What potential difference is required to cause 4.00 A to flow through a resistance of 330 Ω?

A) 12.1 V
B) 82.5 V
C) 334 V
D) 1320 V

Question 48

For the graph shown in the figure, what physical quantity does the slope of the graph represent for a dc circuit?

A) 1/(resistance)
B) resistance
C) potential
D) (potential)²
E) 1/(potential)

Question 49

A charge of 12 C passes through an electroplating apparatus in 2.0 min. What is the average current in the apparatus?

A) 0.10 A
B) 0.60 A
C) 1.0 A
D) 6.0 A

Question 50

What current is flowing in a wire if 0.67 C of charge pass a point in the wire in 0.30 s?

A) 2.2 A
B) 0.67 A
C) 0.30 A
D) 0.20 A

Question 51

A 10-A current flows through a wire for 2.0 min. (e = 1.60 × 10^-19 C)
(a) How much charge has passed through this wire?
(b) How many electrons have passed any point in the wire?

Question 52

For the graph shown in the figure, what physical quantity does the slope of the graph represent for a dc circuit?

A) 1/(resistance)
B) resistance
C) potential
D) (potential)²
E) 1/(potential)

Question 53

For the graph shown in the figure, what physical quantity does the slope of the graph represent for a dc circuit?

A) 1/(current)
B) resistance
C) 1/(resistance)
D) current
E) resistivity

Question 54

What is the voltage drop across a 5.0-Ω resistor if the current through it is 5.0 A?

A) 100 V
B) 25 V
C) 4.0 V
D) 1.0 V

Question 55

If 3.0 × 10¹⁵ electrons flow through a section of a wire of diameter 2.0 mm in 4.0 s, what is the current in the wire? (e = 1.60 × 10^-19 C)

A) 0.12 mA
B) 0.24 mA
C) 7.5 × 10⁷ A
D) 7.5 × 10¹⁴ A

Question 56

A jeweler needs to electroplate gold, having an atomic mass of 196.97 g/mol, onto a bracelet. He knows that the charge carriers in the ionic solution are singly-ionized gold ions, Au⁺, and has calculated that he must deposit of gold to reach the necessary thickness. How much current does he need to plate the bracelet in 3.0 hours? (e = 1.60 × 10^-19 C, N_A = 6.02 × 10²³ atoms/mol)

A) 9.1 mA
B) 540 mA
C) 33 A
D) 1800 mA

Question 57

A current of 5.0 A flows through an electrical device for 10 seconds. How many electrons flow through this device during this time? (e = 1.60 × 10^-19 C)

A) 0.20
B) 20
C) 2.0
D) 3.1 x
E) 31 x

Question 58

In an electroplating process, it is desired to deposit 40 mg of silver on a metal part by using a current of 2.0 A. How long must the current be allowed to run to deposit this much silver? The silver ions are singly charged, and the atomic mass of silver is 108 g/mol. (e = 1.60 × 10^-19 C, N_A = 6.02 × 10²³ atoms/mol)

A) 16 s
B) 18 s
C) 20 s
D) 22 s

Question 59

The current through a piece of lab equipment must be limited to 2.75 A when it is run by a 120-V dc power supply. What must be the resistance of this equipment?

Question 60

What current is flowing in a resistor if 4.0 × 10¹⁶ electrons pass a point in the resistor in 0.50 s? (e = 1.60 × 10^-19 C)

A) 0.013 A
B) 0.31 A
C) 6.3 A
D) 78 A

Question 61

Calculate the current through a 10.0-m long 22-gauge nichrome wire with a radius of 0.321 mm if it is connected across a 12.0-V battery. The resistivity of the nichrome is 1.00 × 10^-6 Ω ∙ m.

A) 30.9 A
B) 61.8 A
C) 0.388 A
D) 0.776 A

Question 62

A metal bar is 20 cm long and has a rectangular cross-section measuring 1.0 cm × 2.0 cm. What is the voltage drop along its length when it carries a 4000-A current? The resistivity of the metal is 1.68 × 10^-8 Ω ∙ m.

A) 0.67 V
B) 0.34 V
C) 0.067 V
D) 0.034 V

Question 63

A rod is 4.0 m long and has a square cross-section that is 1.5 cm on each side. An ohmmeter measures 0.040 Ω across its ends. What is the resistivity of the material from which this rod is made?

A) 0.023 Ω ∙ m
B) 0.015 Ω ∙ m
C) 1.5 × 10^-4 Ω ∙ m
D) 2.3 × 10^-6 Ω ∙ m

Question 64

A 1.0-mm diameter extension cord is made of metal having a resistivity of 1.68 × 10^-8 Ω ∙ m. When it carries a current of 15 A, what is the potential difference between two points in the cord that are 100 m apart?

A) 12 V
B) 23 V
C) 32 V
D) 41 V

Question 65

A 120-m long metal wire having a resistivity of 1.68 × 10^-8 Ω ∙ m has a resistance of 6.0 Ω. What is the diameter of the wire?

A) 0.065 mm
B) 0.65 mm
C) 0.65 cm
D) 0.65 m

Question 66

A certain metal has a resistivity of 1.68 × 10^-8 Ω ∙ m. You have a long spool of wire made from this metal. If this wire has a diameter of 0.15 mm, how long should you cut a segment so its resistance will be 15 Ω?

A) 16 mm
B) 16 cm
C) 1.6 m
D) 16 m

Question 67

The graph shown in the figure shows the results of measurements of the dc current through a circuit device for various potential differences across it. Assume that all the numbers shown are accurate to two significant figures. What is the resistance of this device?

Question 68

What is the resistance of a cylindrical metal rod 1.0 cm in diameter and 45 m long, if the resistivity of the metal is 1.4 × 10^-8 Ω ∙ m?

A) 0.0063 Ω
B) 0.0080 Ω
C) 0.80 Ω
D) 6.3 Ω

Question 69

A 25-m wire of diameter 0.30 mm draws 0.499 A when connected across a 3.0-V potential difference.
(a) What is the resistance of the wire?
(b) What is the resistivity of the material from which the wire is made?

Question 70

What is the resistance of 1.0 m of a solid cylindrical metal cable having a diameter of 0.40 inches and a resistivity of 1.68 × 10^-8 Ω ∙ m?

A) 0.00012 Ω
B) 0.00021 Ω
C) 0.0012 Ω
D) 0.0021 Ω

Question 71

A light bulb operating at 110 V draws 1.40 A of current. What is its resistance?

A) 12.7 Ω
B) 78.6 Ω
C) 109 Ω
D) 154 Ω

Question 72

The resistivity of gold is at a temperature of 20°C. A gold wire that is 0.50 mm in diameter and 44 cm long carries a current of 380 mA. How many electrons each second pass a given cross section of the wire at 20°C? (e = 1.60 × 10^-19C)

A) 2.4 × 10¹⁸
B) 2.4 × 10¹⁷
C) 1.2 × 10²²
D) 2.8 × 10¹⁴
E) 6.3 × 10¹⁵

Question 73

A certain metal wire has a cross-sectional area of 1.0 cm² and a resistivity of 1.7 × 10^-8 Ω ∙ m. How long would it have to be to have a resistance of 1.0 Ω?

A) 5.9 × 10⁶ m
B) 5.9 m
C) 5.9 × 10⁴ m
D) 590 m
E) 5.9 km

Question 74

When a thin copper wire that is 178 m long is connected between a 1.2-V potential difference, a current of 2.0 amps flows through the wire. What is the diameter of this wire? The resistivity of copper is 1.72 × 10^-8 Ω ∙ m.

Question 75

The resistance of a 100-cm wire of cross sectional area 2 × is 400 Ω. What is the resistivity of the material from which this wire is made?

A) 0.80 × Ω ∙ m
B) 8.0 × Ω ∙ m
C) 0.80 × Ω ∙ m
D) 0.80 × Ω ∙ m
E) 8.0 × Ωv

Question 76

A 1.0-m length of nichrome wire has a radius of 0.50 mm and a resistivity of 1.0 × 10^-6 Ω ∙ m. When this wire carries a current of 0.50 A, what is the voltage across its ends?

A) 0.0030 V
B) 0.32 V
C) 0.64 V
D) 1.6 V

Question 77

How much current will be flowing through a length of copper wire with radius if it is connected to a source supplying The resistivity of the metal is 1.68 × 10^-8 Ω ∙ m.

A) 0 A
B) 0 × 10⁸ A
C) 0 nA
D) 0 A

Question 78

A 12-V battery is connected across a 100-Ω resistor. How many electrons flow through the wire in 1.0 min? (e = 1.60 × 10^-19

A) 1.5 × 10¹⁹
B) 2.5 × 10¹⁹
C)
C) 3.5 × 10¹⁹
D) 4.5 × 10¹⁹

Question 79

When a 1.0-m length of metal wire is connected to a battery, a current of flows through it. What is the diameter of the wire? The resistivity of the metal is 2.24 × 10^-8 Ω ∙ m.

A) 12 μm
B) 6.0 μm
C) 24 μm
D) 2.2 μm

Question 80

The graph shown in the figure shows the results of measurements of the dc current through a circuit device for various potential differences across it. Assume that all the numbers shown are accurate to two significant figures. What is the resistance of this device?