Question 1

The magnetic field at a distance of 2 cm from a long straight current-carrying wire is 4 μT. What is the magnetic field at a distance of 1 cm from this wire?

Accepted Answer

A)  2 μT 
B)  4 μT 
C)  6 μT 
D)  8 μT 
E)  10 μT 
A)  2 μT 
B)  4 μT 
C)  6 μT 
D)  8 μT 
E)  10 μT D

Question 2

A 2.0-m straight wire carrying a current of 0.60 A is oriented parallel to a uniform magnetic field of 0.50 T. What is the magnitude of the magnetic force on it?

Accepted Answer

A)  zero 
B)  0.15 N 
C)  0.30 N 
D)  0.60 N 
A)  zero 
B)  0.15 N 
C)  0.30 N 
D)  0.60 N A

Question 3

The magnetic field due to the current in a long, straight wire is 8.0 μT at a distance of 4.0 cm from the center of the wire. What is the current in the wire? (μ0 = 4π × 10-7 T ∙ m/A)

Accepted Answer

A)  0.20 A 
B)  0.40 A 
C)  0.80 A 
D)  3.2 A 
E)  1.6 A 
A)  0.20 A 
B)  0.40 A 
C)  0.80 A 
D)  3.2 A 
E)  1.6 A E

Question 4

If a calculated quantity has units of T ∙ m/A, that quantity could be

Accepted Answer

A)  an electric field. 
B)  an electric potential. 
C)  μ0. 
D)  a magnetic field. 
E)  a magnetic torque. 
A)  an electric field. 
B)  an electric potential. 
C)  μ0. 
D)  a magnetic field. 
E)  a magnetic torque.

Question 5

A straight wire that is 0.60 m and carrying a current of 2.0 A is placed at an angle with respect to the magnetic field of strength 0.30 T. If the wire experiences a force of magnitude 0.18 N, what angle does the wire make with respect to the magnetic field?

Accepted Answer

A)  20° 
B)  25° 
C)  30° 
D)  35° 
E)  60° 
A)  20° 
B)  25° 
C)  30° 
D)  35° 
E)  60°

Question 6

A charged particle is observed traveling in a circular path of radius R in a uniform magnetic field. If the particle were traveling twice as fast, the radius of the circular path would be

Accepted Answer

A)  2R. 
B)  4R. 
C)  8R. 
D)  R/2. 
E)  R/4. 
A)  2R. 
B)  4R. 
C)  8R. 
D)  R/2. 
E)  R/4.

Question 7

Two long parallel wires are placed side-by-side on a horizontal table. If the wires carry current in opposite directions,

Accepted Answer

A)  one wire is lifted slightly while the other wire is forced downward against the table's surface. 
B)  both wires are lifted slightly. 
C)  the wires pull toward each other. 
D)  the wires push away from each other. 
A)  one wire is lifted slightly while the other wire is forced downward against the table's surface. 
B)  both wires are lifted slightly. 
C)  the wires pull toward each other. 
D)  the wires push away from each other.

Question 8

Alpha particles, each having a charge of +2e and a mass of 6.64 ×10-27 kg, are accelerated in a uniform $0.50 \mathrm {~T}$ magnetic field to a final orbit radius of $0.50 \mathrm {~m}$ The field is perpendicular to the velocity of the particles. What is the kinetic energy of an alpha particle in the final orbit? (1 eV = 1.60 × 10-19 J, e = 1.60 × 10-19C)

Accepted Answer

A)  3.0 MeV 
B)  2.6 MeV 
C)  3.4 MeV 
D)  3.9 MeV 
E)  4.3MeV 
A)  3.0 MeV 
B)  2.6 MeV 
C)  3.4 MeV 
D)  3.9 MeV 
E)  4.3MeV

Question 9

Which of the following are units for the magnetic moment? (There could be more than one correct choice.)

Accepted Answer

A)  $\frac { \mathrm { T } } { \mathrm { N } \cdot \mathrm { m } }$ 
B)  A ∙ m2 
C)  N ∙ m/T 
D)  T/m2 
A)  $\frac { \mathrm { T } } { \mathrm { N } \cdot \mathrm { m } }$ 
B)  A ∙ m2 
C)  N ∙ m/T 
D)  T/m2

Question 10

A circular metal loop of radius 10 cm and three long straight wires carry currents of $I _ { 1 } = 20 \mathrm {~A}$ $I _ { 2 } = 50 \mathrm {~A}$ $I _ { 3 } = 20 \mathrm {~A}$ and $I _ { 4 } = 40 \mathrm {~A}$ as shown in the figure. Each of the straight wires is 20 cm from the center of the loop. The axes are shown in the figure, with the +z-axis coming out of the paper. What is the y component of the resultant magnetic field at the center of the loop? (μ0 = 4π × 10-7 T ∙ m/A)

Accepted Answer

A)  -54 μT 
B)  -60 μT 
C)  -50 μT 
D)  +60 μT 
E)  +50 μT 
A)  -54 μT 
B)  -60 μT 
C)  -50 μT 
D)  +60 μT 
E)  +50 μT

Question 11

A proton moving at 5.0 × 104 m/s horizontally enters a region where a magnetic field of 0.12 T is present, directed vertically downward. What magnitude force acts on the proton due to this field?
(e = 1.60 × 10-19C)

Accepted Answer

Question 12

How much current must flow through a long straight wire for the magnetic field strength to be 1.0 mT at 1.0 cm from a wire? 
(μ0 = 4π × 10-7 T ∙ m/A)

Accepted Answer

A)  50 mA 
B)  9.2 A 
C)  16 A 
D)  50 A 
E)  5.0 mA 
A)  50 mA 
B)  9.2 A 
C)  16 A 
D)  50 A 
E)  5.0 mA

Question 13

How much current must pass through a 400-turn ideal solenoid that is 4.0 cm long to generate a 1.0-T magnetic field at the center? (μ0 = 4π × 10-7 T ∙ m/A)

Accepted Answer

A)  0.013 A 
B)  13 A 
C)  22 A 
D)  40 A 
E)  80 A 
A)  0.013 A 
B)  13 A 
C)  22 A 
D)  40 A 
E)  80 A

Question 14

A geophysicist measures the magnetic force on a proton that is moving vertically downward at a point 1.996 km/s at the earth's equator. At that location, the earth's magnetic magnetic field is horizontal and has a strength of 0.40 × 10-4 T. What are the magnitude and direction of the force she will measure? (e = 1.60 × 10-19C)

Accepted Answer

1.3 × 10^-20 N

Question 15

A flat coil containing 25 identical loops carries 6.4 A of current. When it is placed in a uniform magnetic field of 0.22 T that is oriented parallel to the plane of the coil, the magnetic torque on it is 3.7 N ∙ m.
(a) What is the magnetic moment of the coil?
(b) What is the area of each loop?

Accepted Answer

(a) 17 A ∙

Question 16

A particle carrying a charge of +e travels in a circular path of radius R in a uniform magnetic field. If instead the particle carried a charge of +2e, the radius of the circular path would have been

Accepted Answer

A)  2R. 
B)  4R. 
C)  8R. 
D)  R/2. 
E)  R/4. 
A)  2R. 
B)  4R. 
C)  8R. 
D)  R/2. 
E)  R/4.

Question 17

A wire lying in the plane of this page carries a current directly toward the top of the page. What is the direction of the magnetic force this current produces on an electron that is moving perpendicular to the page and outward from it on the left side of the wire?

Accepted Answer

A)  perpendicular to the page and towards you 
B)  perpendicular to the page and away from you 
C)  toward the top of the page 
D)  toward the bottom of the page 
E)  The force is zero. 
A)  perpendicular to the page and towards you 
B)  perpendicular to the page and away from you 
C)  toward the top of the page 
D)  toward the bottom of the page 
E)  The force is zero.

Question 18

A wire is carrying current vertically downward. What is the direction of the force on this wire due to Earth's magnetic field?

Accepted Answer

A)  horizontally towards the north 
B)  horizontally towards the south 
C)  horizontally towards the east 
D)  horizontally towards the west 
E)  vertically upward 
A)  horizontally towards the north 
B)  horizontally towards the south 
C)  horizontally towards the east 
D)  horizontally towards the west 
E)  vertically upward

Question 19

What is the magnetic moment of a rectangular loop having 120 turns that carries 6.0 A if its dimensions are 4.0 cm × 8.0 cm?

Accepted Answer

A)  0.23 A ∙ m2 
B)  2.3 A ∙ m2 
C)  23 A ∙ m2 
D)  230 A ∙ m2 
A)  0.23 A ∙ m2 
B)  2.3 A ∙ m2 
C)  23 A ∙ m2 
D)  230 A ∙ m2

Question 20

An electron moves with a speed of 5.0 × 104 m/s perpendicular to a uniform magnetic field of magnitude 0.20 T. What is the magnitude of the magnetic force on the electron? (e = 1.60 × 10-19C)

Accepted Answer

A)  4.4 × 10-14 N 
B)  1.6 × 10-15 N 
C)  5 × 10-20 N 
D)  2.6 × 10-24 N 
E)  zero 
A)  4.4 × 10-14 N 
B)  1.6 × 10-15 N 
C)  5 × 10-20 N 
D)  2.6 × 10-24 N 
E)  zero

Exam 24: Magnetic Fields and Forces

The magnetic field at a distance of 2 cm from a long straight current-carrying wire is 4 μT. What is the magnetic field at a distance of 1 cm from this wire?

A 2.0-m straight wire carrying a current of 0.60 A is oriented parallel to a uniform magnetic field of 0.50 T. What is the magnitude of the magnetic force on it?

The magnetic field due to the current in a long, straight wire is 8.0 μT at a distance of 4.0 cm from the center of the wire. What is the current in the wire? (μ0 = 4π × 10-7 T ∙ m/A)

If a calculated quantity has units of T ∙ m/A, that quantity could be

A straight wire that is 0.60 m and carrying a current of 2.0 A is placed at an angle with respect to the magnetic field of strength 0.30 T. If the wire experiences a force of magnitude 0.18 N, what angle does the wire make with respect to the magnetic field?

A charged particle is observed traveling in a circular path of radius R in a uniform magnetic field. If the particle were traveling twice as fast, the radius of the circular path would be

Two long parallel wires are placed side-by-side on a horizontal table. If the wires carry current in opposite directions,

Which of the following are units for the magnetic moment? (There could be more than one correct choice.)

A proton moving at 5.0 × 104 m/s horizontally enters a region where a magnetic field of 0.12 T is present, directed vertically downward. What magnitude force acts on the proton due to this field? (e = 1.60 × 10-19C)

How much current must flow through a long straight wire for the magnetic field strength to be 1.0 mT at 1.0 cm from a wire? (μ0 = 4π × 10-7 T ∙ m/A)

How much current must pass through a 400-turn ideal solenoid that is 4.0 cm long to generate a 1.0-T magnetic field at the center? (μ0 = 4π × 10-7 T ∙ m/A)

A flat coil containing 25 identical loops carries 6.4 A of current. When it is placed in a uniform magnetic field of 0.22 T that is oriented parallel to the plane of the coil, the magnetic torque on it is 3.7 N ∙ m. (a) What is the magnetic moment of the coil? (b) What is the area of each loop?

A particle carrying a charge of +e travels in a circular path of radius R in a uniform magnetic field. If instead the particle carried a charge of +2e, the radius of the circular path would have been

A wire lying in the plane of this page carries a current directly toward the top of the page. What is the direction of the magnetic force this current produces on an electron that is moving perpendicular to the page and outward from it on the left side of the wire?

A wire is carrying current vertically downward. What is the direction of the force on this wire due to Earth's magnetic field?

What is the magnetic moment of a rectangular loop having 120 turns that carries 6.0 A if its dimensions are 4.0 cm × 8.0 cm?

An electron moves with a speed of 5.0 × 104 m/s perpendicular to a uniform magnetic field of magnitude 0.20 T. What is the magnitude of the magnetic force on the electron? (e = 1.60 × 10-19C)

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The magnetic field due to the current in a long, straight wire is 8.0 μT at a distance of 4.0 cm from the center of the wire. What is the current in the wire? (μ₀ = 4π × 10^-7 T ∙ m/A)

A proton moving at 5.0 × 10⁴ m/s horizontally enters a region where a magnetic field of 0.12 T is present, directed vertically downward. What magnitude force acts on the proton due to this field? (e = 1.60 × 10^-19C)

How much current must flow through a long straight wire for the magnetic field strength to be 1.0 mT at 1.0 cm from a wire? (μ₀ = 4π × 10^-7 T ∙ m/A)

How much current must pass through a 400-turn ideal solenoid that is 4.0 cm long to generate a 1.0-T magnetic field at the center? (μ₀ = 4π × 10^-7 T ∙ m/A)

An electron moves with a speed of 5.0 × 10⁴ m/s perpendicular to a uniform magnetic field of magnitude 0.20 T. What is the magnitude of the magnetic force on the electron? (e = 1.60 × 10^-19C)