Deck 17: Current and Resistance

Question 1

A high-voltage transmission line of diameter 2 cm and length 150 km carries a steady current of 1 000 A.If the conductor is copper with a free charge density of 8 × 10²⁸ electrons/m³,how long does it take one electron to travel the full length of the cable? (e = 1.6 × 10−¹⁹ C)

A)6.0 × 10² s
B)6.0 × 10⁴ s
C)6.0 × 10⁶ s
D)6.0 × 10⁸ s
E)6.0 × 10^-10 s

Answer 1

6.0 × 10⁸ s

Question 2

When an electric current exists within a conducting wire,which of the following statements describes the condition of any accompanying electric field?

A)must be zero
B)must be parallel to current flow
C)must be anti-parallel (opposite direction)to current flow
D)must be perpendicular to current flow

Answer 2

must be parallel to current flow

Question 3

​If the current carried by a conductor is increased by a factor of 2,what happens to the electron drift velocity.

A)​It increases by a factor of .
B)​It increases by a factor of 1/2.
C)​It increases by a factor of 2².
D)​It increases by a factor of 2.

Answer 3

​It increases by a factor of 2.

Question 4

When you flip a switch to turn on a light,the delay before the light turns on is determined by:

A)the number of electron collisions per second in the wire.
B)the drift speed of the electrons in the wire.
C)the speed of the electric field moving in the wire.
D)none of these,since the light comes on instantly.

Question 5

The number density of conduction electrons in a metal can be found from the density ρ of the metal,the mass per mole M of the metal,the number of conduction electrons per metal atom,and Avogadro's number N_A.If we assume one conduction electron per atom,which of the following gives the number density of conduction electrons for a given metal?

A)N_A ρM
B)N_A ρ /M
C)N_A M /ρ
D)N_A /ρM

Question 6

A wire 1 mm in diameter is connected to one end of a wire of the same material 2 mm in diameter of twice the length.A voltage source is connected to the wires and a current is passed through the wires.If it takes time T for the average conduction electron to traverse the 1-mm wire,how long does it take for such an electron to traverse the 2-mm wire?

A)T/4
B)T
C)4T
D)8T

Question 7

The charge flowing through a light bulb attached to a 12.0-V battery in 11.0 s is 30.0 C.What is the total energy delivered to the filament during this process?

A)12.0 J
B)360 J
C)3 960 J
D)132 J
E)690 J

Question 8

A beam of protons in an accelerator incident on a metal plate carries a current of 150 $\mu$ A.How many protons strike the plate in 24.0 s?

A)1.60E+5
B)3.60E+9
C)2.25E+16
D)3.91E+13

Question 9

A lightbulb drawing a current of 0.60 A is run for 2.0 hours.How many electrons pass through the bulb during this process?

A)2.7 × 10²²
B)1.4 × 10¹⁹
C)5.4 × 10²⁵
D)4.3 × 10³

Question 10

The charge flowing through a light bulb attached to a 12.0-V battery in 13.0 s is 30.0 C.What is the average power supplied by the battery during this process?

A)360 W
B)12.0 W
C)27.7 W
D)5.20 W
E)30.0 W

Question 11

Materials having resistance changes as voltage or current varies are called:

A)ohmic.
B)inohmic.
C)nonohmic.
D)deohmic.

Question 12

Wire A and Wire B are each carrying the same current.If the diameter of Wire A is twice that of Wire B,how does the drift velocity v_dA in Wire A compare to that in in Wire B?

A)v_dA = v_dB
B)v_dA = 2 v_dB
C)v_dA = v_dB /2
D)v_dA = v_dB /4

Question 13

In a certain material there is a current of 18 A flowing through a surface to the right,and there is an equal amount of positive and negative charge passing through the surface producing the current.How much negative charge passes through the surface?

A)9 C/s toward the right
B)9 C/s toward the left
C)18 C/s toward the right
D)18 C/s toward the left
E)36 C/s toward the left

Question 14

To measure the current through and the voltage across a resistor in a circuit,you should place the ammeter in _____ with the resistor and the voltmeter in _____ with the resistor.

A)series,series
B)parallel,series
C)parallel,parallel
D)series,parallel

Question 15

A wire carries a steady current of 0.30 A over a period of 20 s.What total charge passes through the wire in this time interval?

A)67 C
B)20 C
C)6.0 C
D)0.015 C
E)0.30 C

Question 16

The size of the electric current in an electrical conductor is a function of which of the following?

A)velocity of charge carriers
B)conductor cross-sectional area
C)density of charge carriers
D)All of the above choices are valid.

Question 17

If a metallic wire of cross-sectional area 4.0 × 10−⁶ m² carries a current of 7.0 A and has a mobile charge density of 4.24 × 10²⁸ carriers/m³,what is the average drift velocity of the mobile charge carriers? (charge value = 1.6 × 10−¹⁹ C)

A)1.8E+3 m/s
B)1.7E+3 m/s
C)4.1E-4 m/s
D)2.6E-4 m/s
E)7.0E-6 m/s

Question 18

The current in an electron beam in a cathode-ray tube is measured to be 50 µA.How many electrons hit the screen in 7.0 s? (e = 1.6 × 10−¹⁹ C)

A)4.4 × 10¹¹ electrons
B)3.5 × 10¹³ electrons
C)2.2 × 10¹⁵ electrons
D)3.1 × 10¹⁸ electrons
E)2.7 × 10¹⁷ electrons

Question 19

A 300-A·h battery can deliver how many coulombs starting from a full charge?

A)4.8 × 10³
B)4.3 × 10⁴
C)7.2 × 10⁵
D)1.1 × 10⁶

Question 20

If the current in a wire is tripled,what effect does this have on the electron drift velocity in the wire?

A)It stays the same.
B)It triples.
C)It decreases by a factor of three.
D)It increases by a factor of nine.

Question 21

Two cylindrical resistors are made of the same material and have the same resistance.The resistors,R₁ and R₂,have different radii,r₁ and r₂,and different lengths,L₁ and L₂.Which of the following relative values for radii and lengths would result in equal resistances?

A)r₁ = r₂ and L₁ = 2L₂
B)2r₁ = r₂ and L₁ = 2L₂
C)r₁ = r₂ and 4L₁ = L₂
D)2r₁ = r₂ and 4L₁ = L₂

Question 22

A metallic conductor has a resistivity of 35 × 10−⁶ Ω⋅m.What is the resistance of a piece that is 20 m long and has a uniform cross-sectional area of 4.0 × 10−⁶ m²?

A)0.44 Ω
B)180 Ω
C)2.3 Ω
D)7.0 Ω
E)2 800 Ω

Question 23

A copper cable needs to carry a current of 160 A with a power loss of only 2.0 W/m.What is the required radius of the copper cable? (The resistivity of copper is 1.7 × 10−⁸ Ω⋅m).

A)0.43 cm
B)0.83 cm
C)1.7 cm
D)2.6 cm
E)0.33 cm

Question 24

A wire has resistance R.A second wire has twice the length,twice the diameter,and twice the resistivity of the first wire.What is its resistance?

A)8R
B)R
C)R/4
D)The resistance is not given.

Question 25

Three wires of the same diameter and length are made from three different metals: copper (ρ​ = 1.7 × 10^-8 Ω·m),aluminum (ρ​ = 2.7 × 10^-8 Ω·m),and silver (ρ​ = 1.6 × 10^-8 Ω·m).Which wire has the least resistance?

A)the aluminum wire
B)the silver wire
C)the copper wire
D)Since insufficient information is given to find the resistance of each wire,one cannot find the answer.

Question 26

The unit of electric resistance,the ohm,is equivalent to which of the following?

A)V/A
B)V⋅m
C)A/s
D)A/m

Question 27

How long is a wire made from 100 cm³ of copper if its resistance is 4.0 ohms? The resistivity of copper is 1.7 × 10^-5 Ω·m.

A)4.9 m
B)1.7 × 10² m
C)2.6 × 10² m
D)1.5 × 10³ m
E)24 m

Question 28

A length L of wire has a voltage V across its ends while a current I runs through the wire.If a voltage 3V were applied to another length of this same wire from the same coil and the same current were found to run through it,what is the length of this second wire?

A)
B)
C)
D)

Question 29

A Nichrome wire has a radius of 1.3 mm and a resistivity of 1.5 × 10−⁶ Ω⋅m.What is the resistance per unit length of this wire?

A)0.37 Ω/m
B)8.0 Ω/m
C)3.6 Ω/m
D)0.28 Ω/m
E)1.2 Ω/m

Question 30

A flashlight bulb operating at a voltage of 5.0 V has a resistance of 7.0 Ω.How many electrons pass through the bulb filament per second (e = 1.6 × 10−¹⁹ C)?

A)1.1E+16
B)5.6E+21
C)2.2E+17
D)4.5E+18
E)8.8E+19

Question 31

Number 10 copper wire (radius = 1.5 mm)is commonly used for electrical installations in homes.What is the voltage drop in 20 m of #10 copper wire if it carries a current of 12 A? (The resistivity of copper is 1.7 × 10−⁸ Ω⋅m. )

A)0.58 V
B)0.48 V
C)2.7 V
D)2.4 V
E)0.34 V

Question 32

You measure a 20-V potential difference across a 7.0-Ω resistor.What is the current flowing through it?

A)140 A
B)2.9 A
C)27 A
D)13 A
E)5.2 A

Question 33

Two wires with the same resistance have the same diameter but different lengths.If wire 1 has length L₁ and wire 2 has length L₂,how do L₁ and L₂ compare if wire 1 is made from copper and wire 2 is made from aluminum? The resistivity of copper is 1.7 × 10^-5 Ω·m and the resistivity of aluminum is 2.82 × 10^-5 Ω·m.

A)L₁ = 1.7 L₂
B)L₁ = 0.60 L₂
C)L₁ = 2.8 L₂
D)L₁ = 0.36 L₂

Question 34

A resistor is made of a material that has a resistivity that is proportional to the current going through it.If the voltage across the resistor is doubled,what happens to the current through it?

A)It doubles.
B)It quadruples.
C)It increases by a factor of 2^3/2.
D)It increases by a factor of 2^1/2.

Question 35

A 0.20-m-long metal rod has a radius of 3.0 cm and a resistance of 2.5 × 10−⁵ Ω.What is the resistivity of the metal?

A)1.1E-8 Ω⋅m
B)3.5E-7 Ω⋅m
C)1.0E-8 Ω⋅m
D)1.8E-8 Ω⋅m
E)1.2E-7 Ω⋅m

Question 36

If a light bulb has half the resistance of a 110-W light bulb,what would be its wattage? Assume both bulbs are attached to the same 160-V circuit.

A)220 W
B)55 W
C)1.5 W
D)330 W
E)More information is needed.

Question 37

A Nichrome wire has a radius of 1.3 mm and a resistivity of 1.5 × 10−⁶ Ω⋅m.If the wire carries a current of 1.8 A,what is the potential difference per unit length along this wire?

A)0.19 V/m
B)0.51 V/m
C)0.66 V/m
D)6.4 V/m
E)5 V/m

Question 38

If a certain resistor obeys Ohm's law,its resistance will change:

A)as the voltage across the resistor changes.
B)as the current through the resistor changes.
C)as the energy given off by the electrons in their collisions changes.
D)none of the above,since resistance is a constant for the given resistor.

Question 39

The unit of electric current,the ampere,is equivalent to which of the following?

A)V⋅Ω
B)V/Ω
C)Ω⋅m
D)V/s

Question 40

Replacing a wire resistor with another of the same material and length but with three times the diameter will have the effect of changing the resistance by what factor?

A)1/3
B)1/9
C)3
D)9

Question 41

The quantity volt is equivalent to which of the following?

A)J⋅m
B)J⋅C
C)C/Ω
D)J/C

Question 42

​A light bulb is connected to a 12-V battery.Because light bulbs are non-Ohmic,the resistance of the bulb is not constant,but increases as the bulb gets hotter.As the bulb heats up,which value remains unchanged?

A)​The power consumed by the bulb.
B)​The current through the bulb.
C)​The voltage across the bulb.
D)​All the above change.

Question 43

A tungsten wire is used to determine the melting point of indium.The resistance of the tungsten wire is 3.000 Ω at 20.0°C and increases to 4.850 Ω as the indium starts to melt.α_tungsten = 4.50 × 10−³ (°C)−¹.What is the melting temperature of indium?

A)132°C
B)157°C
C)351°C
D)731°C

Question 44

If a 10-V battery,with negligible internal resistance,and a 15-Ω resistor are connected in series,what is the amount of electrical energy transformed to heat per coulomb of charge that flows through the circuit?

A)0.67 J
B)1.5 J
C)10 J
D)150 J
E)25 J

Question 45

A wire of length L is uniformly stretched to triple its original length.By what factor does its resistance change?

A)1,i.e. ,no change
B)3
C)9
D)

Question 46

The temperature coefficient of resistivity for a "perfect" ohmic material would be:

A)positive and constant.
B)zero.
C)negative.
D)positive and uniformly increasing.

Question 47

A metal wire has a resistance of 31 Ω under room temperature conditions of 15°C.When the wire is heated to 81°C the resistance increases by 0.65 Ω.What is the temperature coefficient of resistivity of this metal?

A)3.2E-4 × 10−⁴ (°C)−¹
B)2.5E-3 × 10−³ (°C)−¹
C)1.4E-2 × 10−³ (°C)−¹
D)3.1E-3 × 10−³ (°C)−¹
E)1.4E-4 × 10−⁴ (°C)−¹

Question 48

A certain material is in a room at 25°C.If the absolute temperature (K)of the material is tripled,its resistance doubles.(Water freezes at 273 K. )What is the value for α,the temperature coefficient of resistivity?

A)0.020 (°C)−¹
B)0.0034 (°C)−¹
C)0.0017 (°C)−¹
D)5.96 (°C)−¹

Question 49

The unit for rate of energy transformation,the watt,in an electric circuit is equivalent to which of the following?

A)V/s
B)A⋅Ω
C)V⋅A
D)V/Ω

Question 50

A resistor is connected to a battery with negligible internal resistance.If you replace the resistor with one that has triple the resistance,by what factor does the power dissipated in the circuit change?

A)1/3
B)1/9
C)3
D)9
E)

Question 51

The resistance of a platinum wire is to be calibrated for low-temperature work.A platinum wire with resistance 1.5 Ω at 30°C is immersed in liquid nitrogen at 93 K (−180°C).If the temperature response of the platinum wire is linear,what is the expected resistance of the platinum wire at −180°C? [α_platinum = 3.92 × 10−³ (°C)−¹].

A)0.265 Ω
B)2.38 Ω
C)2.73 Ω
D)8.48 Ω
E)0.618 Ω

Question 52

The temperature coefficient of resistivity is a quantity that is:

A)always positive.
B)always non-negative.
C)sometimes negative.
D)represented by the symbol σ.

Question 53

By what factor is the resistance of a copper wire changed when its temperature is increased from 30.0°C to 115°C? The temperature coefficient of resistivity for copper = 3.9 × 10−³ (°C)−¹.

A)1.45
B)1.12
C)1.33
D)0.669
E)4.32

Question 54

A metal wire has a resistance of 14.00 Ω at a temperature of 25.0°C.If the same wire has a resistance of 14.55 Ω at 90.0°C,what is the resistance when its temperature is −32.0°C?

A)2.21 Ω
B)13.5 Ω
C)5.13 Ω
D)39.2 Ω
E)13.0 Ω

Question 55

A 50-W light bulb is in a socket supplied with 140 V.What is the current in the bulb?

A)0.36 A
B)2.8 A
C)90 A
D)7 000 A
E)3.8 A

Question 56

If a 600-W heater carries a current of 4.0 A,what is the voltage across the ends of the heating element?

A)2 400 V
B)150 V
C)300 V
D)0.0067 V
E)4.9 V

Question 57

The resistivity of a material is doubled when heated a certain amount.What happens to the resistance of a resistor made of this material when heated the same amount?

A)It doubles.
B)It quadruples.
C)It halves.
D)It stays the same.

Question 58

Carbon has a negative temperature coefficient of resistance of -0.5 × 10^-3 (°C)−¹.What temperature increase would result in a resistance decrease of 1.0% for a carbon resistor?

A)2.0°C
B)20°C..
C)20°C.
D)50°C
E)100°C

Question 59

Three resistors,each of different value,are used in a circuit with a power source supplying 12 volts.For which of the following resistor combinations is the total power supplied the greatest?

A)This cannot be found until it is known which resistor is in series with the parallel pair.
B)all three resistors in series
C)two of the resistors in parallel with the third resistor in series with the parallel pair
D)all three resistors in parallel

Question 60

A 16-Ω platinum wire at 20°C with a temperature coefficient of resistivity of 3.9 × 10−³ (°C)−¹ will have what resistance at 80°C?

A)12 Ω
B)13 Ω
C)20 Ω
D)16 Ω
E)3.7 Ω

Question 61

If a lamp has resistance of 140 Ω when it operates at 130 W,what is the applied voltage?

A)135 V
B)151 V
C)121 V
D)72.9 V
E)108 V

Question 62

An electric car is designed to run off a bank of 14.0-V batteries with total energy storage of 3.00 × 10⁷ J.If the electric motor draws 7 000 W,what current will be delivered to the motor?

A)500 A
B)250 A
C)750 A
D)375 A
E)125 A

Question 63

Which is a unit of power?

A)kWh
B)W/s
C)A⋅Ω
D)J/s

Question 64

An electric car is designed to run off a bank of 15-V batteries with total energy storage of 2.1 × 10⁷ J.If the electric motor draws 4 200 W in moving the car at a steady speed of 14 m/s,how far will the car go before it is "out of juice?"

A)35 km
B)70 km
C)140 km
D)110 km
E)18 km

Question 65

A light bulb has resistance of 175 Ω when operating at 100 V.Find the current in the light bulb.

A)1.8 A
B)0.33 A
C)0.57 A
D)0.76 A
E)1.3 A

Question 66

A high-voltage transmission line carries 1 400 A at 600 000 V.What is the power carried by the line?

A)840 MW
B)370 MW
C)140 MW
D)84 MW
E)233 MW

Question 67

An electric clothes dryer draws 10 A at 220 V.If the clothes put into the dryer have a mass of 10 kg when wet and 3 kg dry,about how long does it take to dry the clothes? (Assume all heat energy goes into vaporizing water,L_v = 2.26 × 10⁶ J/kg).

A)171 min
B)120 min
C)51 min
D)40 min
E)5 min

Question 68

Which is not a force?

A)gravity
B)electrical force
C)voltage
D)friction

Question 69

A steam turbine at an electric power plant delivers 4 500 kW of power to an electrical generator which converts 94% of this mechanical energy into electrical energy.What is the current delivered by the generator if it delivers at 3 500 V?

A)7.3E+2 A
B)1.4E+3 A
C)1.2E+3 A
D)1.1E+3 A
E)8.3E+2 A

Question 70

A 500-W heater carries a current of 4.0 A.How much does it cost to operate the heater for 30 min if electrical energy costs 6.0 cents per kWh?

A)1.5 cents
B)9 cents
C)6.0 cents
D)0.042 cents
E)30 cents

Question 71

A water pump draws about 3.7 A when connected to 220 V.What is the cost (with electrical energy at 6.0 cents per kWh)of running the pump for 7.0 h?

A)2.5 cents
B)9.0 cents
C)34 cents
D)68 cents
E)26 cents

Question 72

A light bulb,sold as long-lasting,is rated 95 W at 145 V.The "increased" lifetime comes from using it at 110 V.Assuming negligible change in resistance at the different voltage,what is its power consumption at 110 V?

A)55 W
B)170 W
C)190 W
D)47 W
E)110 W

Question 73

If a 500-W heater carries a current of 4.00 A,what is the resistance of the heating element?

A)85.7 Ω
B)42.8 Ω
C)31.3 Ω
D)11.2 Ω

Question 74

If a lamp has a resistance of 265 Ω when it operates at 250 W,what current does it carry?

A)1.0 A
B)0.94 A
C)0.97 A
D)1.1 A
E)1.9 A

Question 75

A solar panel measures 80 cm × 57 cm.In direct sunlight,the panel delivers 3.1 A at 15 V.If the intensity of sunlight is 1 000 W/m²,what is the efficiency of the solar panel in converting solar energy into electrical energy?

A)20%
B)15%
C)10%
D)5%
E)8%

Question 76

A high-voltage transmission line carries 1 000 A at 700 kV for a distance of 200 miles.If the resistance in the wire is 1 Ω/mile,what is the power loss due to resistive losses?

A)20 kW
B)200 kW
C)20 MW
D)200 MW
E)200 W

Question 77

The heating coil of a hot water heater has a resistance of 17 Ω and operates at 300 V.How long a time is required to raise the temperature of 115 kg of water from 18°C to 75°C? (The specific heat for water = 10³ cal/kg⋅°C and 1.0 cal = 4.186 J).

A)1.5 h
B)1.9 h
C)0.45 h
D)1.4 h
E)0.50 h

Question 78

Suppose that a voltage surge produces 140 V for a moment in a 115-V line.What will temporarily be the output of a 100-W light bulb assuming its resistance does not change?

A)170 W
B)122 W
C)67.5 W
D)148 W
E)74.1 W

Question 79

An electric toaster requires 1 300 W at 150 V.What is the resistance of the heating coil?

A)2.9 Ω
B)74 Ω
C)34 Ω
D)17 Ω
E)38 Ω

Question 80

Which process will double the power given off by a resistor?

A)doubling the current while doubling the resistance
B)doubling the current by making a resistance half as big
C)doubling the current by doubling the voltage
D)doubling the current while making the voltage half as big