Chapter 26: The Magnetic Field

Section 26-1: The Force Exerted by a Magnetic Field, and Concept

Checks 26-1 and 26-2

The direction of any magnetic field is specified as the direction that the north pole of a compass needle points toward when the needle is aligned in the field. Suppose that the direction of the magnetic field were instead specified as the direction pointed toward by the south pole of a compass needle aligned in the field. Would the right-hand rule for force then give the direction of the magnetic force on the moving positive charge, or would a left-hand rule be required?

A. The right-hand rule would still work.

B. A left-hand rule would be required.

The direction of any magnetic field is specified as the direction that the north pole of a compass needle points toward when the needle is aligned in the field. Suppose that the direction of the magnetic field were instead specified as the direction pointed toward by the south pole of a compass needle aligned in the field. Would the right-hand rule for force then give the direction of the magnetic force on the moving positive charge, or would a left-hand rule be required?

A. The right-hand rule would still work.

B. A left-hand rule would be required.

The particle in the figure

A. is positively charged.

B. is negatively charged.

C. could be negatively or positively charged.

The particle in the figure

A. is positively charged.

B. is negatively charged.

C. could be negatively or positively charged.

The phenomenon of magnetism is best understood in terms of

a. the existence of magnetic poles.

b. the magnetic fields associated with the movement of charged particles.

c. gravitational forces between nuclei and orbital electrons.

d. electrical fluids.

e. None of these is correct.

The phenomenon of magnetism is best understood in terms of

A. the existence of magnetic poles.

B. the magnetic fields associated with the movement of charged particles.

C. gravitational forces between nuclei and orbital electrons.

D. electrical fluids.

E. None of these is correct.

The left diagram shows a positively charged particle is moving with velocity v in a magnetic field B. Using the arrows in the right diagram, what is the direction of the magnetic force on the particle?

The left diagram shows a positively charged particle is moving with velocity v in a magnetic field B. Using the arrows in the right diagram, what is the direction of the magnetic force on the particle?

The left diagram shows a force F on a negatively charged particle moving a magnetic field B. Using the arrows in the right diagram, what is the direction of the velocity of the particle?

The left diagram shows a force F on a negatively charged particle moving a magnetic field B. Using the arrows in the right diagram, what is the direction of the velocity of the particle?

If the magnetic field vector is directed toward the north and a positively charged particle is moving toward the east, what is the direction of the magnetic force on the particle?

a. up

b. west

c. south

d. down

e. east

If the magnetic field vector is directed toward the north and a positively charged particle is moving toward the east, what is the direction of the magnetic force on the particle?

A. up

B. west

C. south

D. down

E. east

A positively charged particle is moving northward in a magnetic field. The magnetic force on the particle is toward the northeast. What is the direction of the magnetic field?

A. up

B. northeast

C. southwest

D. down

E. This situation cannot exist.

A positively charged particle is moving northward in a magnetic field. The magnetic force on the particle is toward the northeast. What is the direction of the magnetic field?

A. up

B. northeast

C. southwest

D. down

E. This situation cannot exist.

The SI unit of magnetic field is the tesla (T). This is equivalent to

A. N · s/(C · m)

B. N · C/(s · m)

C. N · m/s2

D. C/(A · s)

E. None of these is correct.

The SI unit of magnetic field is the tesla (T). This is equivalent to

A. N · s/(C · m)

B. N · C/(s · m)

C. N · m/s2

D. C/(A · s)

E. None of these is correct.

The region of space around a moving proton contains

a. a magnetic field only.

b. an electric field only.

c. both an electric and a magnetic field.

d. neither an electric nor a magnetic field.

The region of space around a moving proton contains

A. a magnetic field only.

B. an electric field only.

C. both an electric and a magnetic field.

D. neither an electric nor a magnetic field.

The magnetic force on a charged particle

a. depends on the sign of the charge on the particle.

b. depends on the velocity of the particle.

c. depends on the magnetic field at the particle's instantaneous position.

d. is at right angles to both the velocity and the direction of the magnetic field.

e. is described by all of these.

The magnetic force on a charged particle

A. depends on the sign of the charge on the particle.

B. depends on the velocity of the particle.

C. depends on the magnetic field at the particle's instantaneous position.

D. is at right angles to both the velocity and the direction of the magnetic field.

E. is described by all of these.

An electron is traveling horizontally east in the magnetic field of the earth near the equator. The direction of the force on the electron is

a. zero

b. north

c. south

d. upward

e. downward

An electron is traveling horizontally east in the magnetic field of the earth near the equator. The direction of the force on the electron is

A. zero

B. north

C. south

D. upward

E. downward

A current I flows in a wire that is oriented as shown. Which of the vectors represent the magnetic field that results in a maximum force on the wire?

A current I flows in a wire that is oriented as shown. Which of the vectors represent the magnetic field that results in a maximum force on the wire?

A wire of length L carries a current I, going from West to East, in the presence of a magnetic field B pointing vertically up. The wire moves a distance d to the south. The work done by the magnetic force on the moving charges is

A. +ILBd

B. -ILBd

C. +IL2B/d

D. -IL2B/d

E. zero

A wire of length L carries a current I, going from West to East, in the presence of a magnetic field B pointing vertically up. The wire moves a distance d to the south. The work done by the magnetic force on the moving charges is

A. +ILBd

B. -ILBd

C. +IL2B/d

D. -IL2B/d

E. zero

Chapter 26: The Magnetic Field

Section 26-2: Motion of a Point Charge in a Magnetic Field

A particle with charge q and mass m is moving with speed v in the +x direction enters a magnetic field of strength B pointing in the +y direction. The work done by the magnetic force on the particle as it travels one semi-circle is

A. mqvB

B. mv2

C. qvB

D. zero

E. mv/qB

A particle with charge q and mass m is moving with speed v in the +x direction enters a magnetic field of strength B pointing in the +y direction. The work done by the magnetic force on the particle as it travels one semi-circle is

A. mqvB

B. mv2

C. qvB

D. zero

E. mv/qB

A positively charged particle moves with speed v in the positive x direction. A uniform magnetic field of magnitude B exists in the negative z direction. You want to balance the magnetic force with an electric field so that the particle will continue along a

straight line. The electric field should be in the

A. positive x direction.

B. positive z direction.

C. negative y direction.

D. negative x direction.

E. negative z direction.

A positively charged particle moves with speed v in the positive x direction. A uniform magnetic field of magnitude B exists in the negative z direction. You want to balance the magnetic force with an electric field so that the particle will continue along a

straight line. The electric field should be in the

A. positive x direction.

B. positive z direction.

C. negative y direction.

D. negative x direction.

E. negative z direction.

A 7Li nucleus with a charge of +3e and a mass of 7 u and a proton with a charge of +e and a mass of 1 u are both moving in a plane perpendicular to a magnetic field . The two particles have the same momentum. The ratio of the radius of curvature of the path of the proton (Rp) to that of the 7Li nucleus

(RLi) is

A. Rp/RLi = 3

B. Rp/RLi = 1/3

C. Rp/RLi = 1/7

D. Rp/RLi = 3/7

E. None of these is correct.

A 7Li nucleus with a charge of +3e and a mass of 7 u and a proton with a charge of +e and a mass of 1 u are both moving in a plane perpendicular to a magnetic field . The two particles have the same momentum. The ratio of the radius of curvature of the path of the proton (Rp) to that of the 7Li nucleus

(RLi) is

A. Rp/RLi = 3

B. Rp/RLi = 1/3

C. Rp/RLi = 1/7

D. Rp/RLi = 3/7

E. None of these is correct.

A doubly ionized oxygen atom 16O++ is moving in the same uniform magnetic field as an alpha particle. The velocities of both particles are at right angles to the magnetic field. The paths of the particles have the same radius of curvature. The ratio of the energy of the alpha particle to that of the 16O2+ ion is

A. E /EO = 1/1

B. E /EO = 1/4

C. E /EO = 1/16

D. E /EO = 4/1

E. None of these is correct.

A doubly ionized oxygen atom 16O++ is moving in the same uniform magnetic field as an alpha particle. The velocities of both particles are at right angles to the magnetic field. The paths of the particles have the same radius of curvature. The ratio of the energy of the alpha particle to that of the 16O2+ ion is

A. E /EO = 1/1

B. E /EO = 1/4

C. E /EO = 1/16

D. E /EO = 4/1

E. None of these is correct.

Electrons travel at an initial velocity v0. They pass through a set of deflection plates, between which there exists an electric field which deflects them upwards toward point b. In which direction should a magnetic field be applied so that the electrons land undeflected at a?

Electrons travel at an initial velocity v0. They pass through a set of deflection plates, between which there exists an electric field which deflects them upwards toward point b. In which direction should a magnetic field be applied so that the electrons land undeflected at a?

An electron moves with speed v in the positive x direction. A uniform magnetic field of magnitude B exists in the positive y direction. As the electron moves through this region, it is

A. deflected in the positive y direction.

B. deflected in the positive z direction.

C. deflected in the negative y direction.

D. deflected in the negative z direction.

E. undeviated in its motion.

An electron moves with speed v in the positive x direction. A uniform magnetic field of magnitude B exists in the positive y direction. As the electron moves through this region, it is

A. deflected in the positive y direction.

B. deflected in the positive z direction.

C. deflected in the negative y direction.

D. deflected in the negative z direction.

E. undeviated in its motion.

All of the charged particles that pass through a certain set of crossed electric and magnetic fields without deflection must have the same

A. mass.

B. speed.

C. momentum.

D. energy.

E. charge-to-mass ratio.

All of the charged particles that pass through a certain set of crossed electric and magnetic fields without deflection must have the same

A. mass.

B. speed.

C. momentum.

D. energy.

E. charge-to-mass ratio.

A small positively charged body is moving horizontally and westward. If it enters a uniform horizontal magnetic field that is directed from north to south, the body is deflected

a. upward.

b. downward.

c. toward the north.

d. toward the south.

e. not at all.

A small positively charged body is moving horizontally and westward. If it enters a uniform horizontal magnetic field that is directed from north to south, the body is deflected

A. upward.

B. downward.

C. toward the north.

D. toward the south.

E. not at all.

A positively charged particle is moving through uniform fields and , which are directed in the positive x and positive y directions, respectively. If there is no resultant force on the particle, then its velocity is in the

A. positive x direction.

B. positive y direction.

C. negative x direction.

D. positive z direction.

E. negative z direction.

A positively charged particle is moving through uniform fields and , which are directed in the positive x and positive y directions, respectively. If there is no resultant force on the particle, then its velocity is in the

A. positive x direction.

B. positive y direction.

C. negative x direction.

D. positive z direction.

E. negative z direction.

A uniform magnetic field is parallel to and in the direction of the positive z axis. For an electron to enter this field and not be deflected by the field, the electron must be traveling in which direction?

A. any direction as long as it is in the xy plane.

B. any direction as long as it is in the xz plane.

C. along the x axis.

D. along the y axis.

E. along the z axis.

A uniform magnetic field is parallel to and in the direction of the positive z axis. For an electron to enter this field and not be deflected by the field, the electron must be traveling in which direction?

A. any direction as long as it is in the xy plane.

B. any direction as long as it is in the xz plane.

C. along the x axis.

D. along the y axis.

E. along the z axis.

The track ABC in the figure is a reproduction of the path of a charged particle in a cloud chamber. If the magnetic field is perpendicular to this sheet of paper and directed into the paper, the particle A. has a positive charge and has moved from C to A.

B. has a negative charge and has moved from C to A.

C. has a positive charge and has moved from A to C.

D. has a negative charge and has moved from A to C.

The track ABC in the figure is a reproduction of the path of a charged particle in a cloud chamber. If the magnetic field is perpendicular to this sheet of paper and directed into the paper, the particle A. has a positive charge and has moved from C to A.

B. has a negative charge and has moved from C to A.

C. has a positive charge and has moved from A to C.

D. has a negative charge and has moved from A to C.

Chapter 26: The Magnetic Field

Section 26-3: Torques on Current Loops and Magnets

A circular current loop lies in the xy plane and has radius R = 10 cm. The loop has 20 turns and carries a current I = 4 A. The magnetic dipole of the loop is

y

z

xI

B

Rk

k

k

k

k

ˆmA628.0 E.

ˆmA126.0 D.

ˆmA126.0 C.

ˆmA51.2 B.

ˆmA51.2 A.

A circular current loop lies in the xy plane and has radius R = 10 cm. The loop has 20 turns and carries a current I = 4 A. The magnetic dipole of the loop is

y

z

xI

B

Rk

k

k

k

k

ˆmA628.0 E.

ˆmA126.0 D.

ˆmA126.0 C.

ˆmA51.2 B.

ˆmA51.2 A.

A rectangle is bent on two sides at 90 so that one end lies along the xy plane while the other end lies along the xz plane. The length of each bent portion is illustrated on the Figure. A current I flows through the loop. The magnetic dipole of the rectangle is

x

y

z

ab

a

I

correct. is theseof None E.

)ˆˆ( D.

)ˆˆ( C.

)ˆˆ( B.

)ˆˆ( A.

kjabI

jiabI

kjabI

jiabI

A rectangle is bent on two sides at 90 so that one end lies along the xy plane while the other end lies along the xz plane. The length of each bent portion is illustrated on the Figure. A current I flows through the loop. The magnetic dipole of the rectangle is

x

y

z

ab

a

I

correct. is theseof None E.

)ˆˆ( D.

)ˆˆ( C.

)ˆˆ( B.

)ˆˆ( A.

kjabI

jiabI

kjabI

jiabI

Chapter 26: The Magnetic Field

Section 26-4: The Hall Effect

A current I passes through a slab of metal in the presence of a magnetic field B. Between which two sides does a Hall voltage develop? Write the side with the higher potential first.

A. a and b

B. c and d

C. e and f

D. b and a

E. d and c .

B

I a bc

d

e

f

A current I passes through a slab of metal in the presence of a magnetic field B. Between which two sides does a Hall voltage develop? Write the side with the higher potential first.

A. a and b

B. c and d

C. e and f

D. b and a

E. d and c .

B

I a bc

d

e

f

The rectangular aluminum strip in the figure is in a uniform magnetic field, B. The current I is flowing perpendicular to surface 1. Positive charges will accumulate on

A. surface 1.

B. surface 2.

C. surface 3.

D. the surface opposite surface 2.

E. none of these surfaces.

The rectangular aluminum strip in the figure is in a uniform magnetic field, B. The current I is flowing perpendicular to surface 1. Positive charges will accumulate on

A. surface 1.

B. surface 2.

C. surface 3.

D. the surface opposite surface 2.

E. none of these surfaces.