Question 1

At some moment, an electron ( $q = - 1.6 \times 10 ^ { - 19 }$ C) moves with a velocity of 1 m/s orthogonal to a 1-T magnetic field. The force acting on the electron is

Accepted Answer

A)  $0$ N. 
B)  $1.6 \times 10 ^ { - 19 }$ N. 
C)  $1.0$ N. 
D)  $1.0 \times 10 ^ { - 9 }$ N. 
A)  $0$ N. 
B)  $1.6 \times 10 ^ { - 19 }$ N. 
C)  $1.0$ N. 
D)  $1.0 \times 10 ^ { - 9 }$ N. B

Question 2

Consider a closed Gaussian spherical surface that contains a small bar magnet having four poles (two north and two south). The net flux that passes through the sphere

Accepted Answer

A)  is zero. 
B)  is infinite. 
C)  is nonzero but not infinite. 
D)  is small but not zero. 
A)  is zero. 
B)  is infinite. 
C)  is nonzero but not infinite. 
D)  is small but not zero. A

Question 3

The magnitude of the magnetic field of a circular loop of current-bearing wire at the geometric center of a loop of radius r is proportional to

Accepted Answer

A)  1/r. 
B)  1/r2. 
C)  1/r3. 
D)  1/r4. 
A)  1/r. 
B)  1/r2. 
C)  1/r3. 
D)  1/r4. A

Question 4

All of the following are acceptable units for magnetic fields except

Accepted Answer

A)  gauss. 
B)  tesla. 
C)  weber/meter2. 
D)  There are no exceptions. 
A)  gauss. 
B)  tesla. 
C)  weber/meter2. 
D)  There are no exceptions.

Question 5

A wire solenoid with 100 total turns is bent into the shape of a torus (doughnut) having a radius $r = 5$ cm. A 730-mA current passes through the wire. The magnetic field inside the torus is

Accepted Answer

A)  5.6 mT. 
B)  13 mT. 
C)  0.29 mT. 
D)  23 mT. 
A)  5.6 mT. 
B)  13 mT. 
C)  0.29 mT. 
D)  23 mT.

Question 6

Consider a long, straight, thin wire carrying a steady current. The value of $\oint \vec { B } \cdot d \vec { s }$ computed around a circle at some radius (orthogonal from the wire) is

Accepted Answer

A)  larger as the radius is increased. 
B)  smaller as the radius is increased. 
C)  constant (not a function of the radius). 
D)  none of the above. 
A)  larger as the radius is increased. 
B)  smaller as the radius is increased. 
C)  constant (not a function of the radius). 
D)  none of the above.

Question 7

Consider a long, straight, thin wire carrying a 350-mA steady current. The value of $\oint \vec { B } \cdot d \vec { s }$ computed around the circle of radius 3.1 cm (from the wire) is

Accepted Answer

A)  $1.6 \times 10 ^ { - 8 }$ T.m. 
B)  $6.5 \times 10 ^ { - 6 }$ T.m. 
C)  $7.8 \times 10 ^ { - 6 }$ T.m. 
D)  $4.4 \times 10 ^ { - 7 }$ T.m. 
A)  $1.6 \times 10 ^ { - 8 }$ T.m. 
B)  $6.5 \times 10 ^ { - 6 }$ T.m. 
C)  $7.8 \times 10 ^ { - 6 }$ T.m. 
D)  $4.4 \times 10 ^ { - 7 }$ T.m.

Question 8

For magnetic forces under the circumstance of steady currents flowing in closed circuits, it is still possible that

Accepted Answer

A)  Newton's Third Law fails. 
B)  the law of the conservation of momentum fails. 
C)  Both of the first two responses are valid. 
D)  Neither of the first two responses is valid. 
A)  Newton's Third Law fails. 
B)  the law of the conservation of momentum fails. 
C)  Both of the first two responses are valid. 
D)  Neither of the first two responses is valid.

Question 9

All of the following "natural" bodies possess magnetic dipole moments except

Accepted Answer

A)  electrons. 
B)  protons. 
C)  the Earth. 
D)  There are no exceptions. 
A)  electrons. 
B)  protons. 
C)  the Earth. 
D)  There are no exceptions.

Question 10

The magnitude of the magnetic field of a magnetic dipole as a function of the distance r (along the dipole axis) is proportional to

Accepted Answer

A)  1/r. 
B)  1/r2. 
C)  1/r3. 
D)  1/r4. 
A)  1/r. 
B)  1/r2. 
C)  1/r3. 
D)  1/r4.

Question 11

Consider a long, straight, thick wire of radius 1 cm that carries a steady 0.9-A current. The value of the magnetic field 0.5 cm from the center of the wire is

Accepted Answer

A)  $9.0 \times 10 ^ { - 6 }$ T. 
B)  $1.5 \times 10 ^ { - 6 }$ T. 
C)  $7.3 \times 10 ^ { - 6 }$ T. 
D)  $3.0 \times 10 ^ { - 6 }$ T. 
A)  $9.0 \times 10 ^ { - 6 }$ T. 
B)  $1.5 \times 10 ^ { - 6 }$ T. 
C)  $7.3 \times 10 ^ { - 6 }$ T. 
D)  $3.0 \times 10 ^ { - 6 }$ T.

Question 12

The magnetic field produced by an electric charge at rest relative to the observer

Accepted Answer

A)  must be zero. 
B)  may be zero or nonzero. 
C)  must be nonzero. 
D)  A magnetic field cannot be produced by an electric charge. 
A)  must be zero. 
B)  may be zero or nonzero. 
C)  must be nonzero. 
D)  A magnetic field cannot be produced by an electric charge.

Question 13

Consider a long, straight, thick wire of radius 1 cm that carries a steady current. The direction of the magnetic field 0.5 cm from the center of the wire is

Accepted Answer

A)  axial. 
B)  radial. 
C)  tangential. 
D)  none of the above. 
A)  axial. 
B)  radial. 
C)  tangential. 
D)  none of the above.

Question 14

The correct relationship of the magnitudes of the magnetic force Fm between two electrons to the electric force Fe between the same two electrons is always

Accepted Answer

A)  Fm > Fe. 
B)  Fm = Fe. 
C)  Fm e. 
D)  Hold it! There are no such restrictions. 
A)  Fm > Fe. 
B)  Fm = Fe. 
C)  Fm e. 
D)  Hold it! There are no such restrictions.

Question 15

The direction of the magnetic force on a charged particle depends on

Accepted Answer

A)  the direction of the magnetic field. 
B)  the direction of the velocity of the particle. 
C)  the sign of the particle's charge ( $+ / -$ ). 
D)  all of the above. 
A)  the direction of the magnetic field. 
B)  the direction of the velocity of the particle. 
C)  the sign of the particle's charge ( $+ / -$ ). 
D)  all of the above.

Question 16

The magnitude of the magnetic field of a straight (infinitely long) current-bearing wire as a function of the distance r (from the wire) is proportional to

Accepted Answer

A)  1/r. 
B)  1/r2. 
C)  1/r3. 
D)  1/r4. 
A)  1/r. 
B)  1/r2. 
C)  1/r3. 
D)  1/r4.

Question 17

The formula for the magnetic field at a distance z along the axis of a loop of a current-bearing wire with loop radius R is the same as that for a magnetic dipole, provided

Accepted Answer

A) z >> R. B) z = R. C) z << R. D) Hold it! More than one of the previous responses is valid. A) z >> R. B) z = R. C) z << R. D) Hold it! More than one of the previous responses is valid.

Question 18

The dimensions of $\mu _ { 0 }$ are

Accepted Answer

A)  [newtons] [meters]/ [coulombs]. 
B)  [newtons] [meters]/ [coulombs]2. 
C)  [newtons] [seconds]2/ [coulombs]2. 
D)  [newtons] [meters/second]2/ [coulombs]2. 
A)  [newtons] [meters]/ [coulombs]. 
B)  [newtons] [meters]/ [coulombs]2. 
C)  [newtons] [seconds]2/ [coulombs]2. 
D)  [newtons] [meters/second]2/ [coulombs]2.

Question 19

The magnetic force between a moving charge and a second charge is always zero if the second charge

Accepted Answer

A)  is at rest. 
B)  moves along the line joining the two charges. 
C)  Both of the first two responses are valid. 
D)  Neither of the first two responses is valid. 
A)  is at rest. 
B)  moves along the line joining the two charges. 
C)  Both of the first two responses are valid. 
D)  Neither of the first two responses is valid.

Question 20

A ferromagnetic material is used to

Accepted Answer

A)  enhance (make stronger) the magnetic field in a solenoid. 
B)  eliminate completely the magnetic field in a solenoid. 
C)  diminish (make weaker) the magnetic field in a solenoid. 
D)  enhance the capacitance of a solenoid. 
A)  enhance (make stronger) the magnetic field in a solenoid. 
B)  eliminate completely the magnetic field in a solenoid. 
C)  diminish (make weaker) the magnetic field in a solenoid. 
D)  enhance the capacitance of a solenoid.

Exam 29: Magnetic Force and Field

At some moment, an electron ( q=−1.6×10−19q = - 1.6 \times 10 ^ { - 19 }q=−1.6×10−19 C) moves with a velocity of 1 m/s orthogonal to a 1-T magnetic field. The force acting on the electron is

Consider a closed Gaussian spherical surface that contains a small bar magnet having four poles (two north and two south). The net flux that passes through the sphere

The magnitude of the magnetic field of a circular loop of current-bearing wire at the geometric center of a loop of radius r is proportional to

All of the following are acceptable units for magnetic fields except

A wire solenoid with 100 total turns is bent into the shape of a torus (doughnut) having a radius r=5r = 5r=5 cm. A 730-mA current passes through the wire. The magnetic field inside the torus is

Consider a long, straight, thin wire carrying a steady current. The value of ∮B⃗⋅ds⃗\oint \vec { B } \cdot d \vec { s }∮B⋅ds computed around a circle at some radius (orthogonal from the wire) is

Consider a long, straight, thin wire carrying a 350-mA steady current. The value of ∮B⃗⋅ds⃗\oint \vec { B } \cdot d \vec { s }∮B⋅ds computed around the circle of radius 3.1 cm (from the wire) is

For magnetic forces under the circumstance of steady currents flowing in closed circuits, it is still possible that

All of the following "natural" bodies possess magnetic dipole moments except

The magnitude of the magnetic field of a magnetic dipole as a function of the distance r (along the dipole axis) is proportional to

Consider a long, straight, thick wire of radius 1 cm that carries a steady 0.9-A current. The value of the magnetic field 0.5 cm from the center of the wire is

The magnetic field produced by an electric charge at rest relative to the observer

Consider a long, straight, thick wire of radius 1 cm that carries a steady current. The direction of the magnetic field 0.5 cm from the center of the wire is

The correct relationship of the magnitudes of the magnetic force Fm between two electrons to the electric force Fe between the same two electrons is always

The direction of the magnetic force on a charged particle depends on

The magnitude of the magnetic field of a straight (infinitely long) current-bearing wire as a function of the distance r (from the wire) is proportional to

The formula for the magnetic field at a distance z along the axis of a loop of a current-bearing wire with loop radius R is the same as that for a magnetic dipole, provided

The dimensions of μ0\mu _ { 0 }μ0​ are

The magnetic force between a moving charge and a second charge is always zero if the second charge

A ferromagnetic material is used to

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At some moment, an electron ( $q = - 1.6 \times 10 ^ { - 19 }$ C) moves with a velocity of 1 m/s orthogonal to a 1-T magnetic field. The force acting on the electron is

A wire solenoid with 100 total turns is bent into the shape of a torus (doughnut) having a radius $r = 5$ cm. A 730-mA current passes through the wire. The magnetic field inside the torus is

Consider a long, straight, thin wire carrying a steady current. The value of $\oint \vec { B } \cdot d \vec { s }$ computed around a circle at some radius (orthogonal from the wire) is

Consider a long, straight, thin wire carrying a 350-mA steady current. The value of $\oint \vec { B } \cdot d \vec { s }$ computed around the circle of radius 3.1 cm (from the wire) is

The correct relationship of the magnitudes of the magnetic force F_m between two electrons to the electric force F_e between the same two electrons is always

The dimensions of $\mu _ { 0 }$ are