Question 1

A certain fuse "blows" if the current in it exceeds 1.0 A, at which instant the fuse melts with a current density of   What is the diameter of the wire in the fuse?

Accepted Answer

A)  0.45 mm 
B)  0.63 mm 
C)  0.68 mm 
D)  0.91 mm 
A)  0.45 mm 
B)  0.63 mm 
C)  0.68 mm 
D)  0.91 mm A

Question 2

The current supplied by a battery as a function of time is   What is the total number of electrons transported from the positive electrode to the negative electrode from the time the battery is first used until it is essentially dead? (e = 1.60 × 10-19 C)

Accepted Answer

A)  1.2 ×   
B)  4.4 ×   
C)  5.3 ×   
D)  3.3 ×   
A)  1.2 ×   
B)  4.4 ×   
C)  5.3 ×   
D)  3.3 ×   A

Question 3

As current flows through a uniform wire, the wire gets hotter because the electrons stop moving and therefore transform their lost kinetic energy into thermal energy in the wire.

Accepted Answer

A)  True 
B)  False 
A)  True 
B)  False B

Question 4

The resistivity of gold is   at room temperature. A gold wire that is 0.9 mm in diameter and 14 cm long carries a current of 940 mA. What is the electric field in the wire?

Accepted Answer

A)  0.036 V/m 
B)  0.0090 V/m 
C)  0.028 V/m 
D)  0.046 V/m 
E)  0.090 V/m 
A)  0.036 V/m 
B)  0.0090 V/m 
C)  0.028 V/m 
D)  0.046 V/m 
E)  0.090 V/m

Question 5

Two cables of the same length are made of the same material, except that one cable has twice the diameter of the other cable. When the same potential difference is maintained across both cables, which of the following statements are true? (There may be more than one correct choice.)

Accepted Answer

A)  The same current flows through both cables. 
B)  Both cables carry the same current density. 
C)  The electrons have the same drift velocity in both cables. 
D)  The current in the thin cable is twice as great as the current in the thick cable. 
E)  The current in the thin cable is four times as great as the current in the thick cable. 
A)  The same current flows through both cables. 
B)  Both cables carry the same current density. 
C)  The electrons have the same drift velocity in both cables. 
D)  The current in the thin cable is twice as great as the current in the thick cable. 
E)  The current in the thin cable is four times as great as the current in the thick cable.

Question 6

Calculate the current through a 10.0-m long 22 gauge (having radius 0.321 mm) nichrome wire if it is connected to a 12.0-V battery. The resistivity of nichrome is 100 × 10-8 Ω ∙ m.

Accepted Answer

A)  17.5 A 
B)  30.9 A 
C)  61.8 A 
D)  388 mA 
E)  776 mA 
A)  17.5 A 
B)  30.9 A 
C)  61.8 A 
D)  388 mA 
E)  776 mA

Question 7

The figure shows a 2.0-cm diameter roller that turns at 90 rpm. A 4.0-cm wide plastic film is being wrapped onto the roller, and this plastic carries an excess electric charge having a uniform surface charge density of 5.0 nC/cm2. What is the current of the moving film?

Accepted Answer

A)  190 nA 
B)  23 μA 
C)  30 nA 
D)  11 μA 
A)  190 nA 
B)  23 μA 
C)  30 nA 
D)  11 μA

Question 8

A 2.0 mm diameter wire of length 20 m has a resistance of 0.25 Ω. What is the resistivity of the wire?

Accepted Answer

A)  5.0 × 10-7 Ω ∙ m 
B)  3.9 × 10-8 Ω ∙ m 
C)  4.0 × 10-7 Ω ∙ m 
D)  16 × 10-8 Ω ∙ m 
E)  0.25 Ω ∙ m 
A)  5.0 × 10-7 Ω ∙ m 
B)  3.9 × 10-8 Ω ∙ m 
C)  4.0 × 10-7 Ω ∙ m 
D)  16 × 10-8 Ω ∙ m 
E)  0.25 Ω ∙ m

Question 9

A silver wire has a cross sectional area A = 2.0 mm2. A total of 9.4 × 1018 electrons pass through the wire in 3.0 s. The conduction electron density in silver is 5.8 × 1028 electrons/m3 and e = 1.60 × 10-19 C. What is the drift velocity of these electrons?

Accepted Answer

A)  2.7 × 10-5 m/s 
B)  9.1 × 10-5 m/s 
C)  5.2 × 10-5 m/s 
D)  1.1 × 10-5 m/s 
E)  7.4 × 10-5 m/s 
A)  2.7 × 10-5 m/s 
B)  9.1 × 10-5 m/s 
C)  5.2 × 10-5 m/s 
D)  1.1 × 10-5 m/s 
E)  7.4 × 10-5 m/s

Question 10

When a voltage difference is applied to a piece of metal wire, a   current flows through it. If this metal wire is now replaced with a silver wire having twice the diameter of the original wire, how much current will flow through the silver wire? The lengths of both wires are the same, and the voltage difference remains unchanged. (The resistivity of the original metal is 1.68 × 10-8 Ω ∙ m, and the resistivity of silver is 1.59 × 10-8 Ω ∙ m.)

Accepted Answer

A)  21 mA 
B)  19 mA 
C)  11 mA 
D)  5.3 mA 
A)  21 mA 
B)  19 mA 
C)  11 mA 
D)  5.3 mA

Question 11

A wire of resistivity ρ must be replaced in a circuit by a wire of the same material but 4 times as long. If, however, the resistance of the new wire is to be the same as the resistance of the original wire, the diameter of the new wire must be

Accepted Answer

A)  the same as the diameter of the original wire. 
B)  1/2 the diameter of the original wire. 
C)  1/4 the diameter of the original wire. 
D)  2 times the diameter of the original wire. 
E)  4 times the diameter of the original wire. 
A)  the same as the diameter of the original wire. 
B)  1/2 the diameter of the original wire. 
C)  1/4 the diameter of the original wire. 
D)  2 times the diameter of the original wire. 
E)  4 times the diameter of the original wire.

Question 12

Nichrome wire, often used for heating elements, has resistivity of 1.0 × 10-6 Ω ∙ m at room temperature. What length of No. 30 wire (of diameter 0.250 mm) is needed to wind a resistor that has 50 ohms at room temperature?

Accepted Answer

A)  3.66 m 
B)  2.45 m 
C)  0.61 m 
D)  6.54 m 
E)  22.4 m 
A)  3.66 m 
B)  2.45 m 
C)  0.61 m 
D)  6.54 m 
E)  22.4 m

Question 13

A proton beam that carries a total current of 1.3 mA has 10.0 mm diameter. The current density in the proton beam increases linearly with distance from the center. This is expressed mathematically as J(r) = J0 (r/R), where R is the radius of the beam and J0 is the current density at the edge. Determine the value of J0.

Accepted Answer

A)  25 A/   
B)  6.2 A/   
C)  12 A/   
D)  17 A/   
A)  25 A/   
B)  6.2 A/   
C)  12 A/   
D)  17 A/

Question 14

If a current of 2.4 A is flowing in a cylindrical wire of diameter 2.0 mm, what is the average current density in this wire?

Accepted Answer

A)  7.6 × 105 A/m2 
B)  5.2 × 10-6 A/m2 
C)  1.9 × 105 A/m2 
D)  3.6 × 105 A/m2 
E)  21 × 10-6 A/m2 
A)  7.6 × 105 A/m2 
B)  5.2 × 10-6 A/m2 
C)  1.9 × 105 A/m2 
D)  3.6 × 105 A/m2 
E)  21 × 10-6 A/m2

Question 15

If the current density in a wire or radius R is given by J = kr, 0 < r < R, what is the current in the wire?

Accepted Answer

A)  2πkR3/3 
B)  3πkR3/2 
C)  kR3/3 
D)  kR2 
E)  kR2/2 
A)  2πkR3/3 
B)  3πkR3/2 
C)  kR3/3 
D)  kR2 
E)  kR2/2

Question 16

When electric current is flowing in a metal, the electrons are moving

Accepted Answer

A)  at nearly the speed of light. 
B)  at the speed of light. 
C)  at the speed of sound in the metal. 
D)  at the speed of sound in air. 
E)  at none of the above speeds. 
A)  at nearly the speed of light. 
B)  at the speed of light. 
C)  at the speed of sound in the metal. 
D)  at the speed of sound in air. 
E)  at none of the above speeds.

Question 17

A wire has a cross-sectional area of 0.10 mm2. If there are 4.0 × 1028 atoms per cubic meter in this wire, and if each atom contributes 2 free electrons, what is the drift velocity of the electrons when the current in the wire is 6.0 A? (e = 1.60 × 10-19 C)

Accepted Answer

A)  0.0047 m/s 
B)  0.0092 m/s 
C)  0.94 m/s 
D)  0.019 m/s 
A)  0.0047 m/s 
B)  0.0092 m/s 
C)  0.94 m/s 
D)  0.019 m/s

Question 18

What length of a certain metal wire of diameter 0.15 mm is needed for the wire to have a resistance of 15 Ω? The resistivity of this metal is 1.68 × 10-8 Ω ∙ m.

Accepted Answer

A)  16 mm 
B)  16 cm 
C)  1.6 m 
D)  16 m 
E)  160 m 
A)  16 mm 
B)  16 cm 
C)  1.6 m 
D)  16 m 
E)  160 m

Question 19

The figure shows a steady electric current passing through a wire with a narrow region. What happens to the drift velocity of the moving charges as they go from region A to region B and then to region C?

Accepted Answer

A)  The drift velocity decreases from A to B and increases from B to C. 
B)  The drift velocity increases all the time. 
C)  The drift velocity remains constant. 
D)  The drift velocity decreases all the time. 
E)  The drift velocity increases from A to B and decreases from B to C. 
A)  The drift velocity decreases from A to B and increases from B to C. 
B)  The drift velocity increases all the time. 
C)  The drift velocity remains constant. 
D)  The drift velocity decreases all the time. 
E)  The drift velocity increases from A to B and decreases from B to C.

Question 20

The diameter of a 12-gauge copper wire is 0.081 in. The maximum safe current it can carry (in order to prevent fire danger in building construction) is 20 A. At this current, what is the drift velocity of the electrons? The number of electron carriers in 1.0 cm3 of copper is 8.5 × 1022 and e = 1.60 × 10-19 C.

Accepted Answer

A)  0.044 mm/s 
B)  0.44 mm/s 
C)  0.44 cm/s 
D)  0.44 m/s 
E)  4.4 cm/s 
A)  0.044 mm/s 
B)  0.44 mm/s 
C)  0.44 cm/s 
D)  0.44 m/s 
E)  4.4 cm/s

Exam 27: Current and Resistance

A certain fuse "blows" if the current in it exceeds 1.0 A, at which instant the fuse melts with a current density of What is the diameter of the wire in the fuse?

The current supplied by a battery as a function of time is What is the total number of electrons transported from the positive electrode to the negative electrode from the time the battery is first used until it is essentially dead? (e = 1.60 × 10-19 C)

As current flows through a uniform wire, the wire gets hotter because the electrons stop moving and therefore transform their lost kinetic energy into thermal energy in the wire.

The resistivity of gold is at room temperature. A gold wire that is 0.9 mm in diameter and 14 cm long carries a current of 940 mA. What is the electric field in the wire?

Two cables of the same length are made of the same material, except that one cable has twice the diameter of the other cable. When the same potential difference is maintained across both cables, which of the following statements are true? (There may be more than one correct choice.)

Calculate the current through a 10.0-m long 22 gauge (having radius 0.321 mm) nichrome wire if it is connected to a 12.0-V battery. The resistivity of nichrome is 100 × 10-8 Ω ∙ m.

The figure shows a 2.0-cm diameter roller that turns at 90 rpm. A 4.0-cm wide plastic film is being wrapped onto the roller, and this plastic carries an excess electric charge having a uniform surface charge density of 5.0 nC/cm2. What is the current of the moving film?

A 2.0 mm diameter wire of length 20 m has a resistance of 0.25 Ω. What is the resistivity of the wire?

A silver wire has a cross sectional area A = 2.0 mm2. A total of 9.4 × 1018 electrons pass through the wire in 3.0 s. The conduction electron density in silver is 5.8 × 1028 electrons/m3 and e = 1.60 × 10-19 C. What is the drift velocity of these electrons?

A wire of resistivity ρ must be replaced in a circuit by a wire of the same material but 4 times as long. If, however, the resistance of the new wire is to be the same as the resistance of the original wire, the diameter of the new wire must be

Nichrome wire, often used for heating elements, has resistivity of 1.0 × 10-6 Ω ∙ m at room temperature. What length of No. 30 wire (of diameter 0.250 mm) is needed to wind a resistor that has 50 ohms at room temperature?

If a current of 2.4 A is flowing in a cylindrical wire of diameter 2.0 mm, what is the average current density in this wire?

If the current density in a wire or radius R is given by J = kr, 0 < r < R, what is the current in the wire?

When electric current is flowing in a metal, the electrons are moving

A wire has a cross-sectional area of 0.10 mm2. If there are 4.0 × 1028 atoms per cubic meter in this wire, and if each atom contributes 2 free electrons, what is the drift velocity of the electrons when the current in the wire is 6.0 A? (e = 1.60 × 10-19 C)

What length of a certain metal wire of diameter 0.15 mm is needed for the wire to have a resistance of 15 Ω? The resistivity of this metal is 1.68 × 10-8 Ω ∙ m.

The figure shows a steady electric current passing through a wire with a narrow region. What happens to the drift velocity of the moving charges as they go from region A to region B and then to region C?

Concepts of Motion

Kinematics in One Dimension

Vectors and Coordinate Systems

Kinematics in Two Dimensions

Force and Motion

Dynamics I: Motion Along a Line

Newtons Third Law

Dynamics Ii: Motion in a Plane

Work and Kinetic Energy

Interactions and Potential Energy

Impulse and Momentum

Rotation of a Rigid Body

Newtons Theory of Gravity

Fluids and Elasticity

Oscillations

Traveling Waves

Superposition

A Macroscopic Description of Matter

Work, Heat, and the First Law of Thermodynamics

The Micromacro Connection

Heat Engines and Refrigerators

Electric Charges and Forces

The Electric Field

Gausss Law

The Electric Potential

Potential and Field

Fundamentals of Circuits

The Magnetic Field

Electromagnetic Induction

Electromagnetic Fields and Waves

Ac Circuits

Wave Optics

Ray Optics

Optical Instruments

Relativity

The Foundations of Modern Physics

Quantization

Wave Functions and Uncertainty

One-Dimensional Quantum Mechanics

Atomic Physics

Nuclear Physics

Filters

The current supplied by a battery as a function of time is What is the total number of electrons transported from the positive electrode to the negative electrode from the time the battery is first used until it is essentially dead? (e = 1.60 × 10^-19 C)

Calculate the current through a 10.0-m long 22 gauge (having radius 0.321 mm) nichrome wire if it is connected to a 12.0-V battery. The resistivity of nichrome is 100 × 10^-8 Ω ∙ m.

The figure shows a 2.0-cm diameter roller that turns at 90 rpm. A 4.0-cm wide plastic film is being wrapped onto the roller, and this plastic carries an excess electric charge having a uniform surface charge density of 5.0 nC/cm². What is the current of the moving film?

A silver wire has a cross sectional area A = 2.0 mm². A total of 9.4 × 10¹⁸ electrons pass through the wire in 3.0 s. The conduction electron density in silver is 5.8 × 10²⁸ electrons/m³ and e = 1.60 × 10^-19 C. What is the drift velocity of these electrons?

Nichrome wire, often used for heating elements, has resistivity of 1.0 × 10^-6 Ω ∙ m at room temperature. What length of No. 30 wire (of diameter 0.250 mm) is needed to wind a resistor that has 50 ohms at room temperature?

A wire has a cross-sectional area of 0.10 mm². If there are 4.0 × 10²⁸ atoms per cubic meter in this wire, and if each atom contributes 2 free electrons, what is the drift velocity of the electrons when the current in the wire is 6.0 A? (e = 1.60 × 10^-19 C)

What length of a certain metal wire of diameter 0.15 mm is needed for the wire to have a resistance of 15 Ω? The resistivity of this metal is 1.68 × 10^-8 Ω ∙ m.