Question 1

A rod of 2.0-m length and a square (2.0 mm × 2.0 mm)cross section is made of a material with a resistivity of 6.0 × 10−8 Ω ⋅ m.If a potential difference of 0.50 V is placed across the ends of the rod,at what rate is heat generated in the rod?

Accepted Answer

A)  3.0 W
B)  5.3 W
C)  8.3 W
D)  1.3 W
E)  17 W C

Question 2

How many electrons pass through a 20-Ω resistor in 10 min if there is a potential drop of 30 volts across it?

Accepted Answer

A)  5.6 × 1021
B)  7.5 × 1021
C)  9.4 × 1021
D)  1.1 × 1021
E)  3.8 × 1021 A

Question 3

What maximum power can be generated from an 18-V emf using any combination of a 6.0-Ω resistor and a 9.0-Ω resistor?

Accepted Answer

A)  54 W
B)  71 W
C)  90 W
D)  80 W
E)  22 W C

Question 4

Light bulb A is rated at 60 W and light bulb B is rated at 100 W.Both are designed to operate at 110 V.Which statement is correct?

Accepted Answer

A)  The 60 W bulb has a greater resistance and greater current than the 100 W bulb.
B)  The 60 W bulb has a greater resistance and smaller current than the 100 W bulb.
C)  The 60 W bulb has a smaller resistance and smaller current than the 100 W bulb.
D)  The 60 W bulb has a smaller resistance and greater current than the 100 W bulb.
E)  We need to know the resistivities of the filaments to answer this question.

Question 5

The electron density in copper is 8.49 × 1028 electrons/m3.The electron charge is e = −1.60 × 10−19 C.When a 1.00 A current is present in a copper wire with a 0.40 cm2 cross-section,the electron drift velocity,in m/s,with direction defined relative to the current density,is

Accepted Answer

A)  −1.84 × 10−6.
B)  +1.84 × 10−6.
C)  −1.84.
D)  −5.43 × 105.
E)  +5.43 × 105.

Question 6

The temperature coefficient of resistivity of iron is 5.0 × 10−3 / °C;that of carbon is −0.50 × 10−3 / °C.When an iron wire and a carbon rod,each having the same 10 Ω resistance at 20°C,are cooled from that temperature to −80°C,the new ratio of the resistance of the carbon rod to the resistance of the iron wire at the lower temperature is

Accepted Answer

A)  −0.10.
B)  +1.9.
C)  +2.1.
D)  −10.
E)  +10.

Question 7

A conductor of radius r,length 
And resistivity ρ has resistance R.It is melted down and formed into a new conductor,also cylindrical,with one fourth the length of the original conductor.The resistance of the new conductor is

Accepted Answer

A)    R
B)    R
C)  R
D)  4R
E)  16R

Question 8

How much energy is dissipated as heat during a two-minute time interval by a 1.5-kΩ resistor which has a constant 20-V potential difference across its leads?

Accepted Answer

A)  58 J
B)  46 J
C)  32 J
D)  72 J
E)  16 J

Question 9

A cook plugs a 500 W crockpot and a 1 000 W kettle into a 240 V power supply,all operating on direct current.When we compare the two,we find that

Accepted Answer

A)  Icrockpot kettle and Rcrockpot kettle.
B)  Icrockpot kettle and Rcrockpot > Rkettle.
C)  Icrockpot = Ikettle and Rcrockpot = Rkettle.
D)  Icrockpot > Ikettle and Rcrockpot kettle.
E)  Icrockpot > Ikettle and Rcrockpot > Rkettle.

Question 10

If 5.0 × 1021 electrons pass through a 20-Ω resistor in 10 min,what is the potential difference across the resistor?

Accepted Answer

A)  21 V
B)  32 V
C)  27 V
D)  37 V
E)  54 V

Question 11

A small bulb is rated at 7.5 W when operated at 125 V.Its resistance (in ohms)is

Accepted Answer

A)  0.45.
B)  7.5.
C)  17.
D)  940.
E)  2 100.

Question 12

A 4.0-Ω resistor has a current of 3.0 A in it for 5.0 min.How many electrons pass through the resistor during this time interval?

Accepted Answer

A)  7.5 × 1021
B)  5.6 × 1021
C)  6.6 × 1021
D)  8.4 × 1021
E)  2.1 × 1021

Question 13

The heating coil of a hot water heater has a resistance of 20 ohms and operates at 210 V.If electrical energy costs 5.5 cents per kW-hr,what does it cost to raise the 200 kg of water in the tank from 15°C to 80°C? (The specific heat of water is 4 186 J/kg°C)

Accepted Answer

The answer of The heating coil of a hot water...

Question 14

What is the resistance of 1 000 m of 4-mm diameter copper wire? (ρ_Cu = 1.7 × 10^-8 Ω ⋅ m)

Accepted Answer

The answer of What is the resistance of 1 000...

Question 15

Jadeen says that you can increase the resistance of a copper wire by hammering the wire to make it narrower and longer.Arnell says that you can increase its resistance by heating the wire.Which one,if either,is correct,and why?

Accepted Answer

A)  Arnell,because the conductivity of the wire increases when it is heated.
B)  Arnell,because the conductivity of the wire decreases when it is heated.
C)  Jadeen,because the conductivity of a wire is directly proportional to its area and inversely proportional to its length.
D)  Jadeen,because the conductivity of a copper wire does not increase when it is hammered.
E)  Both are correct because (b) and (d) are both correct.

Question 16

An electric device,which heats water by immersing a resistance wire in the water,generates 50 cal of heat per second when an electric potential difference of 12 V is placed across its leads.What is the resistance of the heater wire? (Note: 1 cal = 4.186 J)

Accepted Answer

A)  0.94 Ω
B)  0.81 Ω
C)  0.58 Ω
D)  0.69 Ω
E)  1.5 Ω

Question 17

A rod (length = 80 cm)with a rectangular cross section (1.5 mm × 2.0 mm)has a resistance of 0.20 Ω.What is the resistivity of the material used to make the rod?

Accepted Answer

A)  6.0 × 10−7 Ω ⋅ m
B)  3.8 × 10−7 Ω ⋅ m
C)  7.5 × 10−7 Ω ⋅ m
D)  3.0 × 10−7 Ω ⋅ m
E)  4.8 × 10−7 Ω ⋅ m

Question 18

A nichrome wire and an aluminum wire,each with the same initial resistance,have the same change in resistance when heated separately.(ρAl = 2.82 × 10−8 Ω ⋅ m;αAl = 3.9 × 10−3 / °C;ρnichrome = 1.50 × 10−6 Ω ⋅ m;αnichrome = 0.40 × 10−3 / °C. )The ratio of the temperature change of the nichrome wire to the temperature change of the aluminum wire is

Accepted Answer

A)  0.019.
B)  0.10.
C)  0.18.
D)  9.8.
E)  53.

Question 19

If a mile of 24-gauge copper wire has a resistance of 0.14 kΩ and the resistivity of copper is 1.7 × 10−8 Ω ⋅ m,what is the diameter of the wire? (1 mile = 1.6 km)

Accepted Answer

A)  0.40 mm
B)  0.50 mm
C)  0.63 mm
D)  0.80 mm
E)  0.25 mm

Question 20

In the Drude model of electrical conduction,the current density is directly proportional to

Accepted Answer

A)  the average time interval between successive collisions.
B)  the number of charge carriers per unit volume.
C)  the square of the electron charge.
D)  the electric field present in the wire.
E)  the product of all four quantities listed above.

Exam 27: Current and Resistance

A rod of 2.0-m length and a square (2.0 mm × 2.0 mm) cross section is made of a material with a resistivity of 6.0 × 10−⁸ Ω ⋅ m.If a potential difference of 0.50 V is placed across the ends of the rod,at what rate is heat generated in the rod?

How many electrons pass through a 20-Ω resistor in 10 min if there is a potential drop of 30 volts across it?

What maximum power can be generated from an 18-V emf using any combination of a 6.0-Ω resistor and a 9.0-Ω resistor?

Light bulb A is rated at 60 W and light bulb B is rated at 100 W.Both are designed to operate at 110 V.Which statement is correct?

The electron density in copper is 8.49 × 10²⁸ electrons/m³.The electron charge is e = −1.60 × 10−¹⁹ C.When a 1.00 A current is present in a copper wire with a 0.40 cm² cross-section,the electron drift velocity,in m/s,with direction defined relative to the current density,is

A conductor of radius r,length And resistivity ρ has resistance R.It is melted down and formed into a new conductor,also cylindrical,with one fourth the length of the original conductor.The resistance of the new conductor is

How much energy is dissipated as heat during a two-minute time interval by a 1.5-kΩ resistor which has a constant 20-V potential difference across its leads?

A cook plugs a 500 W crockpot and a 1 000 W kettle into a 240 V power supply,all operating on direct current.When we compare the two,we find that

If 5.0 × 10²¹ electrons pass through a 20-Ω resistor in 10 min,what is the potential difference across the resistor?

A small bulb is rated at 7.5 W when operated at 125 V.Its resistance (in ohms) is

A 4.0-Ω resistor has a current of 3.0 A in it for 5.0 min.How many electrons pass through the resistor during this time interval?

The heating coil of a hot water heater has a resistance of 20 ohms and operates at 210 V.If electrical energy costs 5.5 cents per kW-hr,what does it cost to raise the 200 kg of water in the tank from 15°C to 80°C? (The specific heat of water is 4 186 J/kg°C)

What is the resistance of 1 000 m of 4-mm diameter copper wire? (ρ_Cu = 1.7 × 10^-8 Ω ⋅ m)

Jadeen says that you can increase the resistance of a copper wire by hammering the wire to make it narrower and longer.Arnell says that you can increase its resistance by heating the wire.Which one,if either,is correct,and why?

An electric device,which heats water by immersing a resistance wire in the water,generates 50 cal of heat per second when an electric potential difference of 12 V is placed across its leads.What is the resistance of the heater wire? (Note: 1 cal = 4.186 J)

A rod (length = 80 cm) with a rectangular cross section (1.5 mm × 2.0 mm) has a resistance of 0.20 Ω.What is the resistivity of the material used to make the rod?

If a mile of 24-gauge copper wire has a resistance of 0.14 kΩ and the resistivity of copper is 1.7 × 10−⁸ Ω ⋅ m,what is the diameter of the wire? (1 mile = 1.6 km)

In the Drude model of electrical conduction,the current density is directly proportional to

Exam 27: Current and Resistance

A rod of 2.0-m length and a square (2.0 mm × 2.0 mm) cross section is made of a material with a resistivity of 6.0 × 10−8 Ω ⋅ m.If a potential difference of 0.50 V is placed across the ends of the rod,at what rate is heat generated in the rod?

How many electrons pass through a 20-Ω resistor in 10 min if there is a potential drop of 30 volts across it?

What maximum power can be generated from an 18-V emf using any combination of a 6.0-Ω resistor and a 9.0-Ω resistor?

Light bulb A is rated at 60 W and light bulb B is rated at 100 W.Both are designed to operate at 110 V.Which statement is correct?

The electron density in copper is 8.49 × 1028 electrons/m3.The electron charge is e = −1.60 × 10−19 C.When a 1.00 A current is present in a copper wire with a 0.40 cm2 cross-section,the electron drift velocity,in m/s,with direction defined relative to the current density,is

A conductor of radius r,length And resistivity ρ has resistance R.It is melted down and formed into a new conductor,also cylindrical,with one fourth the length of the original conductor.The resistance of the new conductor is

How much energy is dissipated as heat during a two-minute time interval by a 1.5-kΩ resistor which has a constant 20-V potential difference across its leads?

A cook plugs a 500 W crockpot and a 1 000 W kettle into a 240 V power supply,all operating on direct current.When we compare the two,we find that

If 5.0 × 1021 electrons pass through a 20-Ω resistor in 10 min,what is the potential difference across the resistor?

A small bulb is rated at 7.5 W when operated at 125 V.Its resistance (in ohms) is

A 4.0-Ω resistor has a current of 3.0 A in it for 5.0 min.How many electrons pass through the resistor during this time interval?

The heating coil of a hot water heater has a resistance of 20 ohms and operates at 210 V.If electrical energy costs 5.5 cents per kW-hr,what does it cost to raise the 200 kg of water in the tank from 15°C to 80°C? (The specific heat of water is 4 186 J/kg°C)

What is the resistance of 1 000 m of 4-mm diameter copper wire? (ρCu = 1.7 × 10-8 Ω ⋅ m)

Jadeen says that you can increase the resistance of a copper wire by hammering the wire to make it narrower and longer.Arnell says that you can increase its resistance by heating the wire.Which one,if either,is correct,and why?

An electric device,which heats water by immersing a resistance wire in the water,generates 50 cal of heat per second when an electric potential difference of 12 V is placed across its leads.What is the resistance of the heater wire? (Note: 1 cal = 4.186 J)

A rod (length = 80 cm) with a rectangular cross section (1.5 mm × 2.0 mm) has a resistance of 0.20 Ω.What is the resistivity of the material used to make the rod?

If a mile of 24-gauge copper wire has a resistance of 0.14 kΩ and the resistivity of copper is 1.7 × 10−8 Ω ⋅ m,what is the diameter of the wire? (1 mile = 1.6 km)

In the Drude model of electrical conduction,the current density is directly proportional to

A rod of 2.0-m length and a square (2.0 mm × 2.0 mm) cross section is made of a material with a resistivity of 6.0 × 10−⁸ Ω ⋅ m.If a potential difference of 0.50 V is placed across the ends of the rod,at what rate is heat generated in the rod?

The electron density in copper is 8.49 × 10²⁸ electrons/m³.The electron charge is e = −1.60 × 10−¹⁹ C.When a 1.00 A current is present in a copper wire with a 0.40 cm² cross-section,the electron drift velocity,in m/s,with direction defined relative to the current density,is

If 5.0 × 10²¹ electrons pass through a 20-Ω resistor in 10 min,what is the potential difference across the resistor?

What is the resistance of 1 000 m of 4-mm diameter copper wire? (ρ_Cu = 1.7 × 10^-8 Ω ⋅ m)

If a mile of 24-gauge copper wire has a resistance of 0.14 kΩ and the resistivity of copper is 1.7 × 10−⁸ Ω ⋅ m,what is the diameter of the wire? (1 mile = 1.6 km)