Question 1

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

Question 2

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

Question 3

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. E

Question 4

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

Question 5

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 × 1024
B)   4.4 × 1023
C)   5.3 × 1024
D)   3.3 × 1019

Question 6

In a certain electroplating process gold is deposited by using a current of 14.0 A for 19 minutes. A gold ion, Au+, has a mass of approximately 3.3 × 10-22 g. How many grams of gold are deposited by this process?

Accepted Answer

A)   33 g
B)   16 g
C)   22 g
D)   28 g
E)   97 g

Question 7

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.

Question 8

The current in a wire varies with time according to the equation I(t) = 6.00 A + (4.80 A/s)t, where t is in seconds. How many coulombs of charge pass a cross section of the wire in the time period between t = 0.00 s and t = 3.00 s?

Accepted Answer

The answer of The current in a wire varies with...

Question 9

A cylindrical wire of radius 2.0 mm carries a current of 2.5 A. The potential difference between points on the wire that are 46 m apart is 3.7 V.
(a) What is the electric field in the wire?
(b) What is the resistivity of the material of which the wire is made?

Accepted Answer

The answer of A cylindrical wire of radius 2.0 mm...

Question 10

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

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.

Question 12

The figure shows two connected wires that are made of the same material. The current entering the wire on the left is 2.0 A and in that wire the electron drift speed is vd. What is the electron drift speed in the wire on the right side?

Accepted Answer

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

Question 13

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.

Question 14

A tube of mercury with resistivity 9.84 × 10-7 Ω ∙ m has an electric field inside the column of mercury of magnitude 23 N/C that is directed along the length of the tube. How much current is flowing through this tube if its diameter is 1.0 mm?

Accepted Answer

A)   18 A
B)   180 A
C)   29 A
D)   280 A

Question 15

A narrow copper wire of length L and radius b is attached to a wide copper wire of length L and radius 2b, forming one long wire of length 2L. This long wire is attached to a battery, and a current is flowing through it. If the electric field in the narrow wire is E, the electric field in the wide wire is

Accepted Answer

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

Question 16

How much current will be flowing through a 40.0 m length of cylindrical metal wire with radius 0.0 mm if it is connected to a source supplying 16.0 V? The resistivity of this metal is 1.68 × 10-8 Ω ∙ m.

Accepted Answer

A)   1200 A
B)   9.5 × 108 A
C)   68 nA
D)   710 A

Question 17

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/m2
B)   6.2 A/m2
C)   12 A/m2
D)   17 A/m2

Question 18

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

Question 19

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

Question 20

What must be the diameter of a cylindrical 120-m long metal wire if its resistance is to be 6.0 Ω? The resistivity of this metal is 1.68 × 10-8 Ω ∙ m.

Accepted Answer

A)   0.065 mm
B)   0.65 mm
C)   0.65 cm
D)   0.325 mm
E)   0.0325 mm

Exam 30: Current and Resistance

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?

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?

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

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 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)

In a certain electroplating process gold is deposited by using a current of 14.0 A for 19 minutes. A gold ion, Au⁺, has a mass of approximately 3.3 × 10^-22 g. How many grams of gold are deposited by this process?

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.)

The current in a wire varies with time according to the equation I(t) = 6.00 A + (4.80 A/s)t, where t is in seconds. How many coulombs of charge pass a cross section of the wire in the time period between t = 0.00 s and t = 3.00 s?

A cylindrical wire of radius 2.0 mm carries a current of 2.5 A. The potential difference between points on the wire that are 46 m apart is 3.7 V. (a) What is the electric field in the wire? (b) What is the resistivity of the material of which the wire is made?

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 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

The figure shows two connected wires that are made of the same material. The current entering the wire on the left is 2.0 A and in that wire the electron drift speed is v_d. What is the electron drift speed in the wire on the right side?

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?

A tube of mercury with resistivity 9.84 × 10^-7 Ω ∙ m has an electric field inside the column of mercury of magnitude 23 N/C that is directed along the length of the tube. How much current is flowing through this tube if its diameter is 1.0 mm?

How much current will be flowing through a 40.0 m length of cylindrical metal wire with radius 0.0 mm if it is connected to a source supplying 16.0 V? The resistivity of this metal is 1.68 × 10^-8 Ω ∙ m.

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?

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.

What must be the diameter of a cylindrical 120-m long metal wire if its resistance is to be 6.0 Ω? The resistivity of this metal is 1.68 × 10^-8 Ω ∙ m.