Deck 18: Magnetism

Question 1

We observe that there is no magnetic force exerted on a moving charged particle.From this we can definitely conclude that

A)no magnetic field exists in that region of space.
B)the particle must be moving parallel to the field vector.
C)the particle is moving at right angles to the field vector.
D)either no magnetic field exists or the particle is moving parallel to the field.
E)either no magnetic field exists or the particle is moving perpendicular to the field.

Answer 1

D

Question 2

When a charged particle is moving in a static uniform magnetic field

A)there will always be a magnetic force exerted on it, regardless of its direction of motion.
B)there may be a magnetic force exerted on it which will cause its speed to change.
C)there may be a magnetic force exerted on it, but its speed will not change.
D)there may be a magnetic force exerted on it, but its direction of motion will not change.
E)None of the above statements are true.

Answer 2

C

Question 3

Which one of the following statements is correct?

A)Earth's geographic north pole is the north pole of Earth's magnetic field.
B)Earth's geographic south pole is the south pole of Earth's magnetic field.
C)The north pole of a magnet points towards Earth's geographic north pole.
D)The north pole of a magnet points towards Earth's geographic south pole.
E)None of the above statements is correct.

Answer 3

C

Question 4

A proton,moving north,enters a magnetic field.Because of this field,the proton curves downward.We may conclude that the field must have a component

A)downward.
B)upward.
C)towards the east.
D)towards the west.
E)towards the north.

Question 5

An electron moving in the +y direction,at right angles to a magnetic field,the magnetic force exerted on it is in the -x direction.The direction of the field is in the

A)-x direction.
B)+x direction.
C)+y direction.
D)-z direction.
E)+z direction.

Question 6

An electron,moving south,enters a magnetic field.Because of this field,the electron curves upward.We may conclude that the field must have a component

A)downward.
B)towards the east.
C)upward.
D)towards the west.
E)towards the north.

Question 7

An electron,moving west,enters a magnetic field.Because of this field the electron curves upward.We may conclude that the field must have a component

A)towards the north.
B)towards the south.
C)upward.
D)downward.
E)towards the west.

Question 8

A positive charge is moving to the right,an upward magnetic force exerted on it,as shown in the figure.In which direction must the field have a component?

A)to the right
B)to the left
C)upward
D)out of the page
E)into the page

Question 9

A proton is to orbit Earth at the equator using Earth's magnetic field to exert part of the necessary radial component of the sum of the forces.In what direction should the proton move?

A)upward
B)northward
C)southward
D)eastward
E)westward

Question 10

An electron is moving to the right,as shown in the figure.Suddenly it encounters uniform magnetic field pointing out of the page.Which one of the three paths shown will it follow in the field?

A)path a
B)path b
C)path c

Question 11

Three particles travel through a region of space where the field is out of the page,as shown in the figure.What are the signs of the charges of these three particles?

A)1 is neutral, 2 is negative, and 3 is positive.
B)1 is neutral, 2 is positive, and 3 is negative.
C)1 is positive, 2 is neutral, and 3 is negative.
D)1 is positive, 2 is negative, and 3 is neutral.
E)1 is negative, 2 is neutral, and 3 is positive.

Question 12

A charged particle moving along the +x-axis enters a uniform field pointing along the +z-axis.A uniform electric field is also present.Due to the combined effect of both fields,the particle does not change its velocity.What is the direction of the electric field?

A)along the -y-axis
B)along the +y-axis
C)along the -x-axis
D)along the +x-axis
E)along the -z-axis

Question 13

A proton,moving west,enters a magnetic field.Because of this magnetic field the proton curves upward.We may conclude that the field must have a component

A)towards the west.
B)towards the east.
C)towards the south.
D)towards the north.
E)downward.

Question 14

A proton,moving east,enters a magnetic field.Because of this magnetic field the proton curves downward.We may conclude that the field must have a component

A)towards the south.
B)towards the north.
C)towards the west.
D)upward.
E)downward.

Question 15

A charged particle moving along the +x-axis enters a uniform field pointing along the +z-axis.Because of an electric field along the +y-axis,the charge particle does not change velocity.What is the sign of this particle?

A)positive
B)negative
C)The particle could be either positive or negative.
D)None of the above choices is correct.

Question 16

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

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

Question 17

If you were to cut a small permanent bar magnet in half,

A)one piece would be a magnetic north pole and the other piece would be a south pole.
B)neither piece would be magnetic.
C)each piece would in itself be a smaller bar magnet with both north and south poles.
D)None of these statements is true.

Question 18

A straight bar magnet is initially 4 cm long,with the north pole on the right and the south pole on the left.If you cut the magnet in half,the right half will

A)contain only a north pole.
B)contain a north pole on the right and a south pole on the left.
C)contain only a south pole.
D)no longer contain any poles.

Question 19

If a calculated quantity has units of ,that quantity could be

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

Question 20

An electron moving along the +x-axis enters a magnetic field.If the electron experiences a magnetic deflection in the -y direction,then the field must have a component

A)along the +z-axis
B)along the -z-axis
C)along the -x-axis
D)along the +y-axis
E)along the -y-axis

Question 21

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

A)to the west.
B)to the east.
C)upward.
D)downward.
E)to the north.

Question 22

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

A)perpendicular only to the current.
B)perpendicular only to the field.
C)perpendicular to both the current and the field.
D)in the direction opposite to the current.
E)in same direction as the current.

Question 23

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 through this coil in the direction shown,what is the direction of the force exerted 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 field
D)in the opposite direction of the field
E)The force is zero.

Question 24

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

A)zero.
B)upward.
C)toward the north.
D)toward the south.
E)downward.

Question 25

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

Question 26

After landing on an unexplored Klingon planet,Mr.Spock investigates the direction of the magnetic field by firing a beam of electrons in various directions and by recording the following observations: A magnetic force in the northwest direction is exerted on the clectrons moving upward.
Electrons moving horizontally toward the north are pushed downward.
Electrons moving horizontally toward the southeast are pushed upward.
Mr.Spock therefore concludes that the 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

Question 27

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

A)to the west.
B)to the east.
C)upward.
D)downward.
E)to the north.

Question 28

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 through this coil in the direction shown,what is the direction of the force exerted 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 field
D)in the opposite direction of the field
E)The force is zero.

Question 29

If a calculated quantity has units of ,that quantity could be

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

Question 30

A charged particle moves with a constant speed through a region where a uniform magnetic field is present.If the field points straight upward,the magnetic force exerted 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.

Question 31

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

A)the current is in the direction of the field lines.
B)the current is in the direction opposite to the field lines.
C)the current is at a 180° angle with respect to the field lines.
D)the current is perpendicular to the field lines.
E)the current is at a 0° angle with respect to the field lines.

Question 32

A wire is carrying current vertically downward.What is the direction of the force exerted 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

Question 33

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

A)zero.
B)upward.
C)toward the north.
D)toward the south.
E)downward.

Question 34

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

Question 35

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 through this coil in the direction shown,what is the direction of the force exerted 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 field
D)in the opposite direction of the field
E)The force is zero.

Question 36

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.

Question 37

A charged particle is injected into a uniform magnetic field such that its velocity vector is perpendicular to the field lines.Ignoring the force that Earth exerts on the particle,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.

Question 38

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.

Question 39

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

Question 40

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.

Question 41

A long,straight,horizontal wire carries current toward the east.A proton moves toward the east alongside and just south of the wire.What is the direction of the magnetic force exerted on the proton?

A)toward the north
B)toward the south
C)upward
D)downward
E)toward the east.

Question 42

A long,straight,horizontal wire carries current toward the east.An electron moves toward the east alongside and just south of the wire.What is the direction of the magnetic force exerted on the electron?

A)toward the north
B)toward the south
C)upward
D)downward
E)toward the west.

Question 43

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-carrying wire exerts on an electron that is moving perpendicular to the page and outward from it on the left side of the wire?

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 44

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

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 45

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

A)
B)A ∙ m²
C)N ∙ m/T
D)T/m²

Question 46

A negatively charged particle -Q is moving to the right,directly above a wire having a current I through it to the right,as shown in the figure.In what direction is the magnetic force exerted on the particle by the current-carrying wire?

A)into the page
B)out of the page
C)downward
D)upward
E)The magnetic force is zero because the velocity is parallel to the current.

Question 47

A very long straight current-carrying wire produces a field of 20 mT at a distance d from the wire.To measure a field of 5 mT due to this wire,you would have to go to a distance from the wire of

A)16d.
B)8d.
C)4d.
D)2d.
E)d

Question 48

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

A)2 μT
B)4 μT
C)6 μT
D)8 μT
E)10 μT

Question 49

A horizontal wire carries a current straight toward you.From your point of view,the field caused by this current

A)points directly away from you.
B)points to the left.
C)circles the wire in a clockwise direction.
D)circles the wire in a counter-clockwise direction.

Question 50

Which one of the following statements is correct?

A)When a current-carrying wire is in your right hand, with your thumb in the direction of the current, your fingers point opposite to the direction of the field lines.
B)When a current-carrying wire is in your right hand, with your thumb in the direction of the current, your fingers point in the direction of the field lines.
C)When a current-carrying wire is in your left hand, with your thumb in the direction of the current, your fingers point in the direction of the field lines.

Question 51

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

A)2 μT
B)4 μT
C)6 μT
D)8 μT
E)10 μT

Question 52

A wire lying in the plane of the page carries a current toward the bottom of the page,as shown in the figure.What is the direction of the magnetic force it exerts on an electron that is moving to the left directly toward the wire,as shown?

A)straight into the page
B)straight out of the page
C)directly toward the top of the page
D)directly toward the bottom of the page
E)directly to the left away from the wire

Question 53

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

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 54

A long straight wire carrying a 4-A current is placed along the x-axis as shown in the figure.What is the direction of the field at a point P due to this wire?

A)into the plane of the page
B)out of the plane of the page
C)along the -x-axis
D)along the +x-axis
E)along the +y-axis

Question 55

Two long parallel wires placed side-by-side on a horizontal table carry identical size currents in opposite directions.The wire on your right carries current directly toward you,and the wire on your left carries current directly away from you.From your point of view,the field at a point exactly midway between the two wires

A)points upward.
B)points downward.
C)points toward you.
D)points away from you.
E)is zero.

Question 56

The maximum torque exerted on a flat current-carrying loop occurs when the angle between the plane of the loop's area and the field vector is

A)0°
B)45°
C)90°
D)135°

Question 57

Two long parallel wires placed side-by-side on a horizontal table carry identical current straight toward you.From your point of view,the field at a point exactly between the two wires

A)points upward.
B)points downward.
C)points toward you.
D)points away from you.
E)is zero.

Question 58

A long,straight wire carrying a current is placed along the y-axis.If the direction of the current is in the +y direction,what is the direction of the field due to this wire as you view it in such a way that the current is coming directly toward you?

A)clockwise, around the x-axis
B)counterclockwise, around the x-axis
C)counterclockwise, around the z-axis
D)counterclockwise, around the y-axis
E)clockwise, around the y-axis

Question 59

A flat circular wire loop lies in a horizontal plane on a table and carries current in a counterclockwise direction when viewed from above.At this point,Earth's field points to the north and dips below the horizontal.Which side of the coil tends to lift off of the table due to the magnetic torque on the loop?

A)the north side
B)the east side
C)the south side
D)the west side
E)The entire loop lifts straight up.

Question 60

A vertical wire carries a current vertically downward.To the east of this wire,the field points

A)north.
B)east.
C)south.
D)down.

Question 61

An electron moves with a speed of 8.0 × 10⁶ m/s along the +x-axis.It enters a region where there is a magnetic field of 2.5 T,directed at an angle of 60° to the +x-axis and lying in the xy-plane.Calculate the magnitude of the magnetic force on the electron.(e = 1.60 × 10^-19C)

A)2.8 × 10^-10 N
B)3.2 × 10^-10 N
C)2.8 × 10^-12 N
D)3.2 × 10^-12 N

Question 62

A proton having a speed of 3.0 × 10⁶ m/s in a direction perpendicular to a uniform magnetic field moves in a circle of radius 0.20 m within the field.What is the magnitude of the field? (e = 1.60 × 10^-19 C,m_proton = 1.67 × 10^-27 kg)

A)0.080 T
B)0.16 T
C)0.24 T
D)0.32 T
E)0.36 T

Question 63

A proton moving at 5.0 × 10⁴ m/s horizontally enters a region where a 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)

Question 64

An electron traveling toward the magnetic north with speed 400 km/s enters a region where Earth's field has the magnitude 5.0 × 10^-5 T and is directed downward at 45° below horizontal.What magnitude magnetic force is exerted on the electron? (e = 1.60 × 10^-19C)

Question 65

A proton travels at a speed of 5.0 × 10⁷ m/s through a 1.0-T field.What is the magnitude of the magnetic force exerted by the field on the proton if the angle between the proton's velocity and the field vector is 30°? (e = 1.60 × 10^-19C)

A)2.0 × 10^-14 N
B)4.0 × 10^-14 N
C)2.0 × 10^-12 N
D)4.0 × 10^-12 N

Question 66

Consider two current-carrying circular loops.Both are made from one strand of wire and both carry the same current,but one has twice the radius of the other.If the field at the center of the smaller loop is ₁,what is the field strength at the center of the larger loop?

A)8B₁
B)4B₁
C)2B₁
D)B₁/2
E)B₁/4

Question 67

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

Question 68

In the figure,a small particle of charge -1.9 x C and mass has speed as it enters a region of uniform magnetic field.The particle is initially traveling perpendicular to the magnetic field and is observed to travel in the semicircular path shown with radius R = 5.0 cm.Find the magnitude and direction of the field in the region.

Question 69

A proton moving with a velocity of 4.0 × 10⁴ m/s enters a magnetic field of 0.20 T.If the angle between the velocity of the proton and the direction of the field is 60°,what is the magnitude of the magnetic force exerted on the proton? (e = 1.60 × 10^-19C)

A)1.8 × 10^-15 N
B)0.60 × 10^-15 N
C)1.1 × 10^-15 N
D)2.2 × 10^-15 N

Question 70

An electron moving perpendicular to a uniform magnetic field of 0.22 T moves in a circle with a speed of 1.5 × 10⁷ m/s.What is the radius of the circle? (e = 1.60 × 10^-19 C,m_electron = 9.11 × 10^-31kg)

A)1.5 mm
B)0.22 mm
C)2.2 mm
D)0.39 mm
E)3.9 mm

Question 71

A single current-carrying circular loop of radius R is placed next to a long,straight wire,as shown in the figure.The current I in the wire flows to the right.In which direction must current flow in the loop to produce a net magnetic field of zero at its center?

A)counterclockwise
B)clockwise
C)It could be either clockwise or counterclockwise.
D)The current in the loop should be zero.

Question 72

An electron moves with a speed of 8.0 × 10⁶ m/s along the +x-axis.It enters a region where there is a magnetic field of 2.5 T,directed at an angle of 60° to the +x-axis and lying in the xy-plane.Calculate the magnitude of the acceleration of the electron.(e = 1.60 × 10^-19 C,m_e1 = 9.11 × 10^-31 kg)

A)1.3 × 10¹⁸ m/s²
B)3.0 × 10¹⁸ m/s²
C)1.3 × 10^-18 m/s²
D)3.0 × 10^-18 m/s²
E)0 m/s²

Question 73

A current-carrying loop of wire lies flat on a horizontal tabletop.When viewed from above,the current through the loop is in a counterclockwise sense.For points on the tabletop inside the loop,the field lines caused by this current

A)circle the loop in a clockwise direction.
B)circle the loop in a counterclockwise direction.
C)point straight up.
D)point straight down.

Question 74

A proton is accelerated from rest through 0.50 kV.It then enters a uniform magnetic field of 0.30 T that is oriented perpendicular to its direction of motion.
(a)What is the radius of the path the proton follows in the magnetic field?
(b)How long does it take the proton to make one complete circle in the magnetic field?.

Question 75

An electron moves with a speed of 3.0 × 10⁴ m/s perpendicular to a uniform magnetic field of 0.40 T.What is the magnitude of the magnetic force exerted on the electron? (e = 1.60 × 10^-19C)

A)4.8 × 10^-14 N
B)1.9 × 10^-15 N
C)5 × 10^-20 N
D)2.2 × 10^-24 N

Question 76

An electron moving perpendicular to a uniform magnetic field of 3.2 × 10^-2 T moves in a circle of radius 0.40 cm.How fast is this electron moving? (e = 1.60 × 10^-19 C,m_electron = 9.11 × 10^-31kg)

A)2.2 × 10⁷ m/s
B)1.9 × 10⁷ m/s
C)1.9 × 10⁶ m/s
D)3.0 × 10⁷ m/s
E)0.80 × 10⁷ m/s

Question 77

A proton,with mass 1.67 × 10^-27 kg and charge +1.6 × 10^-19 C,is sent with velocity in the +x direction into a region where there is a uniform field of magnitude in the +y direction.What must be the magnitude and direction of the uniform field in the region if the proton is to pass through undeflected? Assume that the magnetic field has no x component and neglect gravitational effects.

Question 78

A proton moving eastward with a velocity of 5.0 km/s enters a magnetic field of 0.20 T pointing northward.What are the magnitude and direction of the force that the magnetic field exerts on the proton? (e = 1.60 × 10^-19C)

A)0 N
B)1.6 × 10^-16 N upwards
C)1.6 × 10^-16 N downwards
D)1.1 × 10^-16 N eastwards

Question 79

A current-carrying loop of wire lies flat on a horizontal tabletop.When viewed from above,the direction of the current around the loop is in a counterclockwise sense.For points on the tabletop outside the loop,the field lines caused by this current

A)circle the loop in a clockwise direction.
B)circle the loop in a counterclockwise direction.
C)point straight up.
D)point straight down.

Question 80

A long straight wire has a constant current through it to the right.A rectangular metal loop is situated above the wire,and also has a constant current through it,as shown in the figure.Which one of the following statements is true?

A)The net magnetic force exerted on the rectangle is upward, and there is also a nonzero torque exerted on the rectangle.
B)The net magnetic force exerted on the rectangle is zero, and the net torque on it is zero.
C)The net magnetic force exerted on the rectangle is downward, and there is also a nonzero torque on the rectangle.
D)The net magnetic force exerted on the rectangle is zero, but there is a nonzero torque on the rectangle.
E)The net magnetic exerted force on the rectangle is downward, and the net torque on it is zero.