Question 1

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?

Accepted Answer

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

Question 2

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?

Accepted Answer

A) r1 = r2 and L1 = 2L2 
B) 2r1 = r2 and L1 = 2L2 
C) r1 = r2 and 4L1 = L2 
D) 2r1 = r2 and 4L1 = L2 
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 3

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. )

Accepted Answer

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

Question 4

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

Accepted Answer

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

Question 5

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,Lv = 2.26 × 106 J/kg).

Accepted Answer

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

Question 6

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?

Accepted Answer

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

Question 7

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?

Accepted Answer

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. 
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 8

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.

Accepted Answer

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

Question 9

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?

Accepted Answer

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

Question 10

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?

Accepted Answer

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 
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 11

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?

Accepted Answer

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

Question 12

A 7.00-Ω resistor is dissipating 70.0 watts.What are the current through it and the potential difference across it?

Accepted Answer

A) 10.0 A,22.1 V 
B) 22.1 A,3.16 V 
C) 3.16 A,22.1 V 
D) 3.16 A,10.0 V 
E) 10.0 A,70.0 V 
A) 10.0 A,22.1 V 
B) 22.1 A,3.16 V 
C) 3.16 A,22.1 V 
D) 3.16 A,10.0 V 
E) 10.0 A,70.0 V

Question 13

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)

Accepted Answer

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 
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

Question 14

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?

Accepted Answer

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

Question 15

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 NA.If we assume one conduction electron per atom,which of the following gives the number density of conduction electrons for a given metal?

Accepted Answer

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

Question 16

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.

Accepted Answer

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

Question 17

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

Accepted Answer

A) 2.9 Ω 
B) 74 Ω 
C) 34 Ω 
D) 17 Ω 
E) 38 Ω 
A) 2.9 Ω 
B) 74 Ω 
C) 34 Ω 
D) 17 Ω 
E) 38 Ω

Question 18

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?

Accepted Answer

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

Question 19

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?

Accepted Answer

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

Question 20

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

Accepted Answer

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

Exam 17: Current and Resistance

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?

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?

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

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,Lv = 2.26 × 106 J/kg).

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?

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?

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.

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 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 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 7.00-Ω resistor is dissipating 70.0 watts.What are the current through it and the potential difference across it?

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

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

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

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

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Filters

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?

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. )

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).

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?

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 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 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?