Deck 21: Electric Current and Direct-Current Circuits

Question 1

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

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

Answer 1

charge

Question 2

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.

Answer 2

only electrons.

Question 3

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.

Answer 3

The electric potential is lower at point b than at point a.
The current at point b is the same as the current at point a.

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 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 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

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 7

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 8

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 9

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 10

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 11

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 12

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 13

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.

Question 14

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

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

Question 15

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 16

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 17

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 18

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 19

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 20

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.

Question 21

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 22

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 23

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 24

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 25

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 26

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 27

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 28

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 29

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 30

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 31

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 32

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

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

Question 33

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

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

Question 34

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 35

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 36

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 37

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 38

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 39

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 40

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 41

A 5-µF,a 7-µF,and an unknown capacitor C_X are connected in parallel between points a and b as shown in the figure.What do you know about the equivalent capacitance C_ab between a and b? (There could be more than one correct choice. )

A)C_ab > 12 µF
B)C_ab > C_X
C)5 µF < C_ab < 12 µF
D)C_ab < 5 µF
E)C_ab < C_X

Question 42

Suppose you have two capacitors and want to use them to store the maximum amount of energy by connecting them across a voltage source.You should connect them

A)in series across the source.
B)in parallel across the source.
C)It doesn't matter because the stored energy is the same either way.

Question 43

You obtain a 100-W light bulb and a 50-W light bulb.Instead of connecting them in the normal way,you devise a circuit that places them in series across normal household voltage.If each one is an incandescent bulb of fixed resistance,which statement about these bulbs is correct?

A)Both bulbs glow with the same brightness,but less than their normal brightness.
B)Both bulbs glow with the same brightness,but more than their normal brightness.
C)The 100-W bulb glows brighter than the 50-W bulb.
D)The 50-W bulb glows more brightly than the 100-W bulb.

Question 44

Four unequal resistors are connected in series with each other.Which one of the following statements is correct about this combination?

A)The equivalent resistance is equal to that of any one of the resistors.
B)The equivalent resistance is equal to average of the four resistances.
C)The equivalent resistance is less than that of the smallest resistor.
D)The equivalent resistance is less than that of the largest resistor.
E)The equivalent resistance is more than the largest resistance.

Question 45

Three identical capacitors are connected in parallel to a potential source (battery).If a charge of Q flows into this combination,how much charge does each capacitor carry?

A)3Q
B)Q
C)Q/3
D)Q/9

Question 46

A 9-V battery is hooked up to two resistors in series using wires of negligible resistance.One has a resistance of 5 Ω,and the other has a resistance of 10 Ω.Several locations along the circuit are marked with letters,as shown in the figure.Which statements about this circuit are true? (There could be more than one correct choice. )

A)The current is exactly the same at points A,B,C,and D.
B)The current at A is greater than the current at B,which is equal to the current at C,which is greater than the current at D.
C)The current at A is greater than the current at B,which is greater than the current at C,which is greater than the current at D.
D)The potential at B is equal to the potential at C.
E)The potential at D is equal to the potential at C.

Question 47

As more resistors are added in parallel across a constant voltage source,the power supplied by the source

A)increases.
B)decreases.
C)does not change.
D)increases for a time and then starts to decrease.

Question 48

As more resistors are added in series to a constant voltage source,the power supplied by the source

A)increases.
B)decreases.
C)does not change.
D)increases for a time and then starts to decrease.

Question 49

The lamps in a string of decorative lights are connected in parallel across a constant-voltage power source.What happens if one lamp burns out? (Assume negligible resistance in the wires leading to the lamps. )

A)The brightness of the lamps will not change appreciably.
B)The other lamps get brighter equally.
C)The other lamps get brighter,but some get brighter than others.
D)The other lamps get dimmer equally.
E)The other lamps get dimmer,but some get dimmer than others.

Question 50

When unequal resistors are connected in parallel in a circuit,

A)the same current always runs through each resistor.
B)the potential drop is always the same across each resistor.
C)the largest resistance has the largest current through it.
D)the power generated in each resistor is the same.

Question 51

When two or more different capacitors are connected in series across a potential source,which of the following statements must be true? (There could be more than one correct choice. )

A)The total voltage across the combination is the algebraic sum of the voltages across the individual capacitors.
B)Each capacitor carries the same amount of charge.
C)The equivalent capacitance of the combination is less than the capacitance of any of the capacitors.
D)The potential difference across each capacitor is the same.
E)The capacitor with the largest capacitance has the most charge.

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

A 5-µF,a 7-µF,and an unknown capacitor C_X are connected in series between points a and b.What do you know about the equivalent capacitance C_ab between a and b? (There could be more than one correct choice. )

A)C_ab > 12 µF
B)5 µF < C_ab < 7 µF
C)5 µF < C_ab < 12 µF
D)C_ab < 5 µF
E)C_ab < C_X

Question 54

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 55

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 56

When unequal resistors are connected in series across an ideal battery,

A)the same power is dissipated in each one.
B)the potential difference across each is the same.
C)the current flowing in each is the same.
D)the equivalent resistance of the circuit is less than that of the smallest resistor.
E)the equivalent resistance of the circuit is equal to the average of all the resistances.

Question 57

When two or more different capacitors are connected in parallel across a potential source (battery),which of the following statements must be true? (There could be more than one correct choice. )

A)The potential difference across each capacitor is the same.
B)Each capacitor carries the same amount of charge.
C)The equivalent capacitance of the combination is less than the capacitance of any one of the capacitors.
D)The capacitor with the largest capacitance has the largest potential difference across it.
E)The capacitor with the largest capacitance has the most charge.

Question 58

Three identical capacitors are connected in series across a potential source (battery).If a charge of Q flows into this combination of capacitors,how much charge does each capacitor carry?

A)3Q
B)Q
C)Q/3
D)Q/9

Question 59

Four unequal resistors are connected in a parallel with each other.Which one of the following statements is correct about this combination?

A)The equivalent resistance is less than that of the smallest resistor.
B)The equivalent resistance is equal to the average of the four resistances.
C)The equivalent resistance is midway between the largest and smallest resistance.
D)The equivalent resistance is more than the largest resistance.
E)None of the other choices is correct.

Question 60

When different resistors are connected in parallel across an ideal battery,we can be certain that

A)the same current flows in each one.
B)the potential difference across each is the same.
C)the power dissipated in each is the same.
D)their equivalent resistance is greater than the resistance of any one of the individual resistances.
E)their equivalent resistance is equal to the average of the individual resistances.

Question 61

A capacitor C is connected in series with a resistor R across a battery and an open switch.If a second capacitor of capacitance 2C is connected in parallel with the first one,the time constant of the new RC circuit will be

A)the same as before.
B)twice as large as before.
C)three times a large as before.
D)one-half as large as before.
E)one-fourth as large as before.

Question 62

A capacitor C is connected in series with a resistor R across a battery and an open switch.If a second capacitor of capacitance 2C is connected in series with the first one,the time constant of the new RC circuit will be

A)the same as before.
B)larger than before.
C)smaller than before.
D)variable.

Question 63

A 9-V battery is hooked up to two resistors in series.One has a resistance of 5 Ω,and the other has a resistance of 10 Ω.Several locations along the circuit are marked with letters,as shown in the figure.Through which resistor is energy being dissipated at the higher rate?

A)the 10-Ω resistor
B)the 5-Ω resistor
C)Energy is being dissipated by both resistors at the same rate.

Question 64

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 65

A resistor is made out of a wire having a length L.When the ends of the wire are attached across the terminals of an ideal battery having a constant voltage V₀ across its terminals,a current I flows through the wire.If the wire were cut in half,making two wires of length L/2,and both wires were attached across the terminals of the battery (the right ends of both wires attached to one terminal,and the left ends attached to the other terminal),how much current would the battery put out?

A)4I
B)2I
C)I
D)I/2
E)I/4

Question 66

Kirchhoff's junction rule is a statement of

A)the law of conservation of momentum.
B)the law of conservation of charge.
C)the law of conservation of energy.
D)the law of conservation of angular momentum.
E)Newton's second law.

Question 67

Identical light bulbs can be attached to identical ideal batteries in three different ways (A,B,orC),as shown in the figure.The ranking (from lowest to highest)of the total power produced by the battery is

A)B,A,C.
B)A,B,C.
C)C,B,A.
D)A,C,B.

Question 68

A resistor,an uncharged capacitor,a dc voltage source,and an open switch are all connected in series.The switch is closed at time t = 0 s.Which one of the following is a correct statement about this circuit?

A)The charge on the capacitor after four time constants is about 98% of the maximum value.
B)The charge on the capacitor after one time constant is 50% of its maximum value.
C)The charge on the capacitor after one time constant is 1/e of its maximum value.
D)The voltage on the capacitor after one time constant is 1/e of the maximum value.
E)The voltage on this capacitor after one time constant is 100% of its maximum value.

Question 69

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 70

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 71

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 ×
E)31 ×

Question 72

Kirchhoff's loop rule is a statement of

A)the law of conservation of momentum.
B)the law of conservation of charge.
C)the law of conservation of energy.
D)the law of conservation of angular momentum.
E)Newton's second law.

Question 73

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 74

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 75

A resistor,an uncharged capacitor,a dc voltage source,and an open switch are all connected in series.The switch is closed at time t = 0 s.Which one of the following is a correct statement about the circuit?

A)The capacitor charges to its maximum value in one time constant.
B)The capacitor charges to its maximum value in two time constants.
C)The potential difference across the resistor is always equal to the potential difference across the capacitor.
D)Current flows through the circuit even after the capacitor is essentially fully charged.
E)Once the capacitor is essentially fully charged,there is no current in the circuit.

Question 76

In the circuit shown in the figure,the resistor R has a variable resistance.As R is decreased,what happens to the currents?

A)I₁ remains unchanged and I₂ increases.
B)I₁ decreases and I₂ decreases.
C)I₁ decreases and I₂ increases.
D)I₁ increases and I₂ decreases.
E)I₁ increases and I₂ increases.

Question 77

Identical ideal batteries are connected in different arrangements to the same light bulb,as shown in the figure.For which arrangement will the bulb shine the brightest?

A)A
B)B
C)C

Question 78

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

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

Question 79

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 80

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