Question 1

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

Accepted Answer

The radius of the circular path of a charged particle in a magnetic field is directly proportional to the velocity of the particle. Therefore, if the velocity doubles, the radius of the path also doubles.

Question 2

A charged particle is injected into a uniform magnetic field such that its velocity vector is perpendicular to the magnetic field lines. Ignoring the particle's weight, the particle will
A)move in a straight line.
B)follow a spiral path.
C)move along a parabolic path.
D)follow a circular path.

Accepted Answer

When a charged particle is injected into a uniform magnetic field with a velocity vector perpendicular to the magnetic field lines, it experiences a magnetic force perpendicular to both its velocity and the magnetic field lines. This force acts as a centripetal force and causes the particle to move in a circular path. Therefore, the best choice is D- follow a circular path.

Question 3

A proton, moving in a uniform magnetic field, moves in a circle perpendicular to the field lines and takes time T for each circle. If the proton's speed tripled, what would now be its time to go around each circle?
A)9T
B)3T
C)T
D)T/3
E)T/9

Accepted Answer

The time to go around each circle, or the period of the circular motion, is independent of the speed of the proton when moving perpendicular to the magnetic field lines.

Question 4

A charged particle moves with a constant speed through a region where a uniform magnetic field is present. If the magnetic field points straight upward, the magnetic force acting on this particle will be strongest when the particle moves
A)straight upward.
B)straight downward.
C)in a plane parallel to Earth's surface.
D)upward at an angle of 45° above the horizontal.

Accepted Answer

The magnetic force on a charged particle is given by the equation F = qvBsinθ, where q is the magnitude of charge, v is the velocity, B is the magnetic field, and θ is the angle between the velocity of the particle and the direction of the magnetic field. Since the particle is moving with a constant speed, its velocity vector is always tangent to its path, and thus always parallel to the Earth's surface. Therefore, the angle θ between the velocity vector and the upward-pointing magnetic field is always 90°, which means sinθ is always 1. So, the magnetic force is strongest when the particle moves in a plane parallel to Earth's surface.

Question 5

For the horseshoe magnet shown in the figure, the left end is a north magnetic pole and the right end is a south magnetic pole. When the switch is closed in the circuit, which way will the wire between the poles of the horseshoe magnet initially deflect? 
A)to the right
B)to the left
C)upward
D)downward

Accepted Answer

The answer of For the horseshoe magnet shown in the...

Question 6

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

Accepted Answer

The radius of the circular path $r$ for a charged particle moving in a magnetic field is given by $r = \frac{mv}{qB}$, where $m$ is the mass of the particle, $v$ is its velocity, $q$ is its charge, and $B$ is the magnetic field strength. Doubling the charge ($q$ becomes $2e$) while keeping the other factors constant (assuming the kinetic energy and thus the velocity of the particle remains the same) would halve the radius of the path, making the correct answer $R/2$.

Question 7

An electron has an initial velocity to the south but is observed to curve upward as the result of a magnetic field. This magnetic field must have a component
A)to the west.
B)to the east.
C)upward.
D)downward.
E)to the north.

Accepted Answer

By the right-hand rule, if the electron's initial velocity is to the south and it curves upward, then the magnetic field must be perpendicular to the plane formed by the initial velocity and the direction of the upward curvature. This means the magnetic field has a component perpendicular to the initial velocity, which is to the east or west. However, since the electron curves upward, we know the magnetic field must be pointing towards the west. Therefore, the best choice is A) to the west.

Question 8

A rectangular coil, with corners labeled ABCD, has length L and width w. It is placed between the poles of a magnet, as shown in the figure If there is a current I flowing through this coil in the direction shown, what is the direction of the force acting on section AB of this coil? 
A)perpendicular to and into the page
B)perpendicular to and out of the page
C)in the direction of the magnetic field
D)in the opposite direction of the magnetic field
E)The force is zero.

Accepted Answer

The answer of A rectangular coil, with corners labeled ABCD,...

Question 9

When the switch is closed in the circuit shown in the figure, the wire between the poles of the horseshoe magnet deflects upward. From this you can conclude that the left end of the magnet is 
A)a north magnetic pole.
B)a south magnetic pole.
C)There is not enough information given to answer the question.

Accepted Answer

The answer of When the switch is closed in the...

Question 10

If a calculated quantity has units of $\frac { \mathrm { N } } { \mathrm { A } \cdot \mathrm { m } }$ , that quantity could be A)an electric field. B)an electric potential. C)(?)₀. D)a magnetic field. E)a magnetic torque.

Accepted Answer

The answer of If a calculated quantity has units of...

Question 11

A negatively-charged particle moves across a constant uniform magnetic field that is perpendicular to the velocity of the particle. The magnetic force on this particle
A)causes the particle to speed up.
B)causes the particle to slow down.
C)causes the particle to accelerate.
D)is in the same direction as the particle's velocity.
E)is opposite the direction of the particle's velocity.

Accepted Answer

The magnetic force acts perpendicular to the velocity of the particle, changing its direction but not its speed, which is a form of acceleration.

Question 12

A rectangular coil, with corners labeled ABCD, has length L and width w. It is placed between the poles of a magnet, as shown in the figure. If there is a current I flowing through this coil in the direction shown, what is the direction of the force acting on section CD of this coil? 
A)perpendicular to and into the page
B)perpendicular to and out of the page
C)in the direction of the magnetic field
D)in the opposite direction of the magnetic field
E)The force is zero.

Accepted Answer

The answer of A rectangular coil, with corners labeled ABCD,...

Question 13

At a particular instant, an electron moves toward the east in a uniform magnetic field that is directed straight downward. The magnetic force that acts on it is
A)zero.
B)upward.
C)toward the north.
D)toward the south.
E)downward.

Accepted Answer

The magnetic force experienced by a charged particle moving in a magnetic field is given by the equation F = qvBsinθ, where q is the charge of the particle, v is its velocity, B is the magnetic field strength, and θ is the angle between the velocity vector and the magnetic field vector. In this case, the electron is moving to the east and the magnetic field is directed downward, so θ is 90 degrees and sin θ is 1. The electron has a negative charge, so its force is in the opposite direction to that experienced by a positively charged particle. Therefore, the force on the electron is downward, or toward the south.

Question 14

The magnetic force on a current-carrying wire in a magnetic field is the strongest when
A)the current is in the direction of the magnetic field lines.
B)the current is in the direction opposite to the magnetic field lines.
C)the current is at a 180° angle with respect to the magnetic field lines.
D)the current is perpendicular to the magnetic field lines.
E)the current is at a 0° angle with respect to the magnetic field lines.

Accepted Answer

The magnetic force is the strongest when the current is perpendicular to the magnetic field lines. This is because the force on a current-carrying wire is proportional to the product of the magnetic field strength and the component of the current that is perpendicular to the magnetic field lines. When the current is perpendicular to the magnetic field lines, the entire current contributes to the force and therefore the force is strongest.

Question 15

A proton has an initial velocity to the south but is observed to curve upward as the result of a magnetic field. This magnetic field must have a component
A)to the west.
B)to the east.
C)upward.
D)downward.
E)to the north.

Accepted Answer

If the proton is curving upwards, then the magnetic field must exert a force perpendicular to both the proton's velocity and the direction of the magnetic field. Since the initial velocity is to the south, and the proton curves upwards, the force must be directed toward the east. Therefore, the magnetic field must have a component to the east (perpendicular to the plane of motion).

Question 16

At a particular instant, a proton moves toward the east in a uniform magnetic field that is directed straight downward. The magnetic force that acts on it is
A)zero.
B)upward.
C)toward the north.
D)toward the south.
E)downward.

Accepted Answer

The magnetic force on a charged particle moving in a magnetic field is given by the Lorentz force law, which is perpendicular to both the velocity of the particle and the magnetic field direction. Since the proton is moving east and the magnetic field is downward, the magnetic force, according to the right-hand rule, will be toward the north.

Question 17

A wire is carrying current vertically downward. What is the direction of the force on this wire due to Earth's magnetic field?
A)horizontally towards the north
B)horizontally towards the south
C)horizontally towards the east
D)horizontally towards the west
E)vertically upward

Accepted Answer

According to the right-hand rule, if a current-carrying wire is placed vertically and perpendicular to the Earth's magnetic field, the force acting on each electron will be perpendicular to both the direction of the current and the magnetic field, resulting in a force directed eastward. Thus the wire will experience a force in the horizontally towards the east direction.

Question 18

The direction of the force on a current-carrying wire in a magnetic field is
A)perpendicular only to the current.
B)perpendicular only to the magnetic field.
C)perpendicular to both the current and the magnetic field.
D)in the direction opposite to the current.
E)in same direction as the current.

Accepted Answer

The direction of the force on a current-carrying wire in a magnetic field is given by the right-hand rule, where the thumb points in the direction of the current, the fingers point in the direction of the magnetic field, and the palm shows the direction of the force. Therefore, the force is perpendicular to both the current and the magnetic field.

Question 19

After landing on an unexplored Klingon planet, Spock tests for the direction of the magnetic field by firing a beam of electrons in various directions and by recording the following observations: Electrons moving upward feel a magnetic force in the northwest direction.
Electrons moving horizontally toward the north are pushed downward.
Electrons moving horizontally toward the southeast are pushed upward.
Mr. Spock therefore concludes that the magnetic field at this landing site is in which direction?
A)toward the east
B)toward the northeast
C)toward the southwest
D)toward the southeast
E)toward the west

Accepted Answer

From the observations, we can conclude that the magnetic field is pointing towards the northwest-southeast direction. When the electrons are moving upward, they feel a force in the northwest direction. When electrons move horizontally towards the north, they are pushed downward. This implies that the magnetic field is perpendicular to the direction of motion and pointing towards the west. Similarly, when electrons move horizontally towards the southeast, they are pushed upward, which also implies that the magnetic field is perpendicular to the direction of motion and pointing towards the west.

Combining these observations, we can infer that the magnetic field is pointing towards the west-northwest direction. Therefore, the best choice is C) toward the southwest, which is the opposite direction of west-northwest.

Question 20

A rectangular coil, with corners labeled ABCD, has length L and width w. It is placed between the poles of a magnet, as shown in the figure If there is a current I flowing through this coil in the direction shown, what is the direction of the force acting on section BC of this coil? 
A)perpendicular to and into the page
B)perpendicular to and out of the page
C)in the direction of the magnetic field
D)in the opposite direction of the magnetic field
E)The force is zero.

Accepted Answer

The answer of A rectangular coil, with corners labeled ABCD,...

Quiz 24: Magnetic Fields and Forces

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

A charged particle is injected into a uniform magnetic field such that its velocity vector is perpendicular to the magnetic field lines. Ignoring the particle's weight, the particle will

A proton, moving in a uniform magnetic field, moves in a circle perpendicular to the field lines and takes time T for each circle. If the proton's speed tripled, what would now be its time to go around each circle?

A charged particle moves with a constant speed through a region where a uniform magnetic field is present. If the magnetic field points straight upward, the magnetic force acting on this particle will be strongest when the particle moves

For the horseshoe magnet shown in the figure, the left end is a north magnetic pole and the right end is a south magnetic pole. When the switch is closed in the circuit, which way will the wire between the poles of the horseshoe magnet initially deflect?

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

An electron has an initial velocity to the south but is observed to curve upward as the result of a magnetic field. This magnetic field must have a component

A rectangular coil, with corners labeled ABCD, has length L and width w. It is placed between the poles of a magnet, as shown in the figure If there is a current I flowing through this coil in the direction shown, what is the direction of the force acting on section AB of this coil?

When the switch is closed in the circuit shown in the figure, the wire between the poles of the horseshoe magnet deflects upward. From this you can conclude that the left end of the magnet is

If a calculated quantity has units of NA⋅m\frac { \mathrm { N } } { \mathrm { A } \cdot \mathrm { m } }A⋅mN​ , that quantity could be

A negatively-charged particle moves across a constant uniform magnetic field that is perpendicular to the velocity of the particle. The magnetic force on this particle

A rectangular coil, with corners labeled ABCD, has length L and width w. It is placed between the poles of a magnet, as shown in the figure. If there is a current I flowing through this coil in the direction shown, what is the direction of the force acting on section CD of this coil?

At a particular instant, an electron moves toward the east in a uniform magnetic field that is directed straight downward. The magnetic force that acts on it is

The magnetic force on a current-carrying wire in a magnetic field is the strongest when

A proton has an initial velocity to the south but is observed to curve upward as the result of a magnetic field. This magnetic field must have a component

At a particular instant, a proton moves toward the east in a uniform magnetic field that is directed straight downward. The magnetic force that acts on it is

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

The direction of the force on a current-carrying wire in a magnetic field is

A rectangular coil, with corners labeled ABCD, has length L and width w. It is placed between the poles of a magnet, as shown in the figure If there is a current I flowing through this coil in the direction shown, what is the direction of the force acting on section BC of this coil?

If a calculated quantity has units of $\frac { \mathrm { N } } { \mathrm { A } \cdot \mathrm { m } }$ , that quantity could be