Deck 21: Magnetic Forces and Magnetic Fields

Question 1

A charged particle is moving in a uniform, constant magnetic field.Which one of the following statements concerning the magnetic force exerted on the particle is false?

A)The magnetic force does no work on the particle.
B)The magnetic force increases the speed of the particle.
C)The magnetic force changes the velocity of the particle.
D)The magnetic force can act only on a particle in motion.
E)The magnetic force does not change the kinetic energy of the particle.

Answer 1

The magnetic force increases the speed of the particle.

Question 2

Which one of the following statements concerning the magnetic force on a charged particle in a magnetic field is true?

A)The magnetic force is a maximum if the particle is stationary.
B)The magnetic force is zero if the particle moves perpendicular to the field.
C)The magnetic force is a maximum if the particle moves parallel to the field.
D)The magnetic force acts in the direction of motion for a positively charged particle.
E)The magnetic force depends on the component of the particle's velocity that is perpendicular to the field.

Answer 2

The magnetic force depends on the component of the particle's velocity that is perpendicular to the field.

Question 3

Complete the following statement: The magnitude of the magnetic force that acts on a charged particle in a magnetic field is independent of

A)the sign of the charge.
B)the magnitude of the charge.
C)the magnitude of the magnetic field.
D)the direction of motion of the particle.
E)the velocity components of the particle.

Answer 3

the sign of the charge.

Question 4

Two particles move through a uniform magnetic field that is directed out of the plane of the page.The figure shows the paths taken by the two particles as they move through the field.The particles are not subject to any other forces or fields.Which one of the following statements concerning these particles is true?

A)The particles may both be neutral.
B)Particle 1 is positively charged; 2 is negative.
C)Particle 1 is positively charged; 2 is positive.
D)Particle 1 is negatively charged; 2 is negative.
E)Particle 1 is negatively charged; 2 is positive.

Question 5

An proton travels through a region of space with no acceleration.Which one of the following statements is the best conclusion?

A)Both E and B must be zero in that region.
B)E must be zero, but B might be non-zero in that region.
C)E and B might both be non-zero, but they must be mutually perpendicular.
D)B must be zero, but E might be non-zero in that region.
E)E and B might both be non-zero, but they must point in opposite directions.

Question 6

An electron traveling horizontally enters a region where a uniform magnetic field is directed into the plane of the paper as shown.Which one of the following phrases most accurately describes the motion of the electron once it has entered the field?

A)upward and parabolic
B)upward and circular
C)downward and circular
D)upward, along a straight line
E)downward and parabolic

Question 7

Which combination of units can be used to express the magnetic field?

A)kg. m²/C
B)kg . s/C²
C)N . m²/C
D)kg/(C . s)
E)kg .m/(C . s²)

Question 8

A charged particle is launched with a velocity of 5.2 × 10⁴ m/s at an angle of 35° with respect to a 0.0045-T magnetic field.If the magnetic field exerts a force of 0.0026 N on the particle, determine the magnitude of the charge on the particle.

A)11 µC
B)15 µC
C)19 µC
D)23 µC
E)27 µC

Question 9

Which one of the following statements best explains why a constant magnetic field can do no work on a moving charged particle?

A)The magnetic field is conservative.
B)The magnetic force is a velocity dependent force.
C)The magnetic field is a vector and work is a scalar quantity.
D)The magnetic force is always perpendicular to the velocity of the particle.
E)The electric field associated with the particle cancels the effect of the magnetic field on the particle.

Question 10

A particle with a mass of 6.64 × 10^-27 kg and a charge of +3.20 × 10^-19 C is accelerated from rest through a potential difference of 2.45 × 10⁶ V.The particle then enters a uniform 1.60-T magnetic field.If the particle's velocity is perpendicular to the magnetic field at all times, what is the magnitude of the magnetic force exerted on the particle?

A)zero newtons
B)1.14 × 10^-10 N
C)6.55 × 10^-10 N
D)4.09 × 10^-11 N
E)7.87 × 10^-12 N

Question 11

Two electrons are located in a region of space where the magnetic field is zero.Electron A is at rest; and electron B is moving westward with a constant velocity.A non-zero magnetic field directed eastward is then applied to the region.In what direction, if any, will each electron be moving after the field is applied?

A)
B)
C)
D)
E)

Question 12

A proton traveling due west in a region that contains only a magnetic field experiences a vertically upward force (away from the surface of the earth).What is the direction of the magnetic field?

A)north
B)east
C)south
D)west
E)down

Question 13

Two charged particles of equal mass are traveling in circular orbits in a region of uniform, constant magnetic field as shown.The particles are observed to move in circular paths of radii R₁ and R₂ with speeds v₁ and v₂, respectively. As the figure shows, the path of particle 2 has a smaller radius than that of particle 1.Which one of the following statements about this system is false?

A)|v₁/Q₁| < |v₂/Q₂|
B)Particle 2 carries a positive charge.
C)Particle 1 carries a negative charge.
D)Neither particle gains energy from the magnetic field.
E)The particle velocities have no components parallel to the magnetic field.

Question 14

An electron traveling due south enters a region that contains both a magnetic field and an electric field. The electric field lines point due west.It is observed that the electron continues to travel in a straight line due south.In which direction must the magnetic field lines point?

A)up
B)down
C)east
D)west
E)south

Question 15

An electron enters a region that contains a magnetic field directed into the page as shown.The velocity vector of the electron makes an angle of 30° with the +y axis.What is the direction of the magnetic force on the electron when it enters the field?

A)up, out of the page
B)at an angle of 30° below the positive x axis
C)at an angle of 30° above the positive x axis
D)at an angle of 60° below the positive x axis
E)at an angle of 60° above the positive x axis

Question 16

A proton is traveling south as it enters a region that contains a magnetic field.The proton is deflected downward toward the earth.What is the direction of the magnetic field?

A)downward, toward the earth
B)west
C)north
D)east
E)south

Question 17

A mass spectrometer is used to separate two isotopes of uranium with masses m₁ and m₂ where m₂ > m₁.The two types of uranium atom exit an ion source S with the same charge of +e and are accelerated through a potential difference V.The charged atoms then enter a constant, uniform magnetic field B as shown.If r₁ = 0.5049 m and r₂ = 0.5081 m, what is the value of the ratio m₁/m₂?

A)0.9984
B)0.9937
C)0.9874
D)0.9812
E)0.9749

Question 18

An electron traveling due north enters a region that contains a uniform magnetic field that points due east.In which direction will the electron be deflected?

A)east
B)west
C)up
D)down
E)south

Question 19

An electron is moving with a speed of 3.5 × 10⁵ m/s when it encounters a magnetic field of 0.60 T.The direction of the magnetic field makes an angle of 60.0° with respect to the velocity of the electron.What is the magnitude of the magnetic force on the electron?

A)4.9 × 10^-13 N
B)3.2 × 10^-13 N
C)1.7 × 10^-13 N
D)3.4 × 10^-14 N
E)2.9 × 10^-14 N

Question 20

Which one of the following statements concerning permanent magnets is false?

A)The north pole of a permanent magnet is attracted to a south pole.
B)All permanent magnets are surrounded by a magnetic field.
C)The direction of a magnetic field is indicated by the north pole of a compass.
D)Magnetic field lines outside a permanent magnet originate from the north pole and end on the south pole.
E)When a permanent magnet is cut in half, one piece will be a north pole and one piece will be a south pole.

Question 21

A single circular loop of wire of radius 0.45 m carries a constant current of 2.4 A.The loop may be rotated about an axis that passes through the center and lies in the plane of the loop.When the orientation of the normal to the loop with respect to the direction of the magnetic field is 36°, the torque on the coil is 1.5 N .m.What is the magnitude of the uniform magnetic field exerting this torque on the loop?

A)0.37 T
B)1.7 T
C)3.0 T
D)0.46 T
E)0.80 T

Question 22

21-2
A long, straight, vertical segment of wire traverses a magnetic field of magnitude 2.0 T in the direction shown in the diagram.The length of the wire that lies in the magnetic field is 0.060 m.When the switch is closed, a current of 4.0 A flows through the wire from point P to point Q.
A current-carrying, rectangular coil of wire is placed in a magnetic field.The magnitude of the torque on the coil is not dependent upon which one of the following quantities?

A)the magnitude of the current in the loop
B)the direction of the current in the loop
C)the length of the sides of the loop
D)the area of the loop
E)the orientation of the loop

Question 23

A rectangular loop has sides of length 0.06 m and 0.08 m.The wire carries a current of 10 A in the direction shown.The loop is in a uniform magnetic field of magnitude 0.2 T and directed in the positive x direction.What is the magnitude of the torque on the loop?

A)2 × 10^-2 N . m
B)4 × 10^-2 N . m
C)5 × 10^-3 N . m
D)8 × 10^-3 N .m
E)1 × 10^-4 N .m

Question 24

The radius of a coil of wire with N turns is r = 0.28 m.A clockwise current of I_coil = 1.0 A flows in the coil, as shown.A long, straight wire carrying a current I_wire = 29 A toward the left is located 0.04 m from the edge of the coil.The magnetic field at the center of the coil is zero tesla.Determine N, the number of turns.

A)8
B)2
C)6
D)4
E)1

Question 25

Which one of the following statements concerning the magnetic field inside (far from the surface) a long, current-carrying solenoid is true?

A)The magnetic field is zero.
B)The magnetic field is non-zero and nearly uniform.
C)The magnetic field is independent of the number of windings.
D)The magnetic field is independent of the current in the solenoid.
E)The magnetic field varies as 1/r as measured from the solenoid axis.

Question 26

A long, straight wire carries a 6.0-A current that is directed in the positive x direction.When a uniform magnetic field is applied perpendicular to a 3.0-m segment of the wire, the magnetic force on the segment is 0.36 N, directed in the negative y direction, as shown.What are the magnitude and direction of the magnetic field?

A)0.020 T, out of the paper
B)0.020 T, into the paper
C)0.060 T, out of the paper
D)0.060 T, into the paper
E)0.65 T, out of the paper

Question 27

21-1
A beam consisting of five types of ions labeled A, B, C, D, and E enters a region that contains a uniform magnetic field as shown in the figure below.The field is perpendicular to the plane of the paper, but its precise direction is not given.All ions in the beam travel with the same speed.The table below gives the masses and charges of the ions.Note: 1 mass unit = 1.67 × 10^-27 kg and e = 1.6 × 10^-19 C
Which ion falls at position 2?

A)A
B)B
C)C
D)D
E)E

Question 28

Two charged particles are traveling in circular orbits with the same speed in a region of uniform magnetic field that is directed into the page, as shown.The magnitude of the charge on each particle is identical, but the signs of the charges are unequal. Which one of the entries in the table below is correct?

A)
B)
C)
D)
E)

Question 29

The drawing shows two long, thin wires that carry currents in the positive z direction.Both wires are parallel to the z axis.The 50-A wire is in the x-z plane and is 5 m from the z axis.The 40-A wire is in the y-z plane and is 4 m from the z axis.What is the magnitude of the magnetic field at the origin?

A)zero tesla
B)1 × 10^-6 T
C)3 × 10^-6 T
D)4 × 10^-6 T
E)6 × 10^-6 T

Question 30

A loop of wire with a weight of 0.55 N is oriented vertically and carries a current I = 2.25 A.A segment of the wire passes through a magnetic field directed into the plane of the page as shown.The net force on the wire is measured using a balance and found to be zero.What is the magnitude of the magnetic field?

A)zero tesla
B)0.51 T
C)0.84 T
D)1.2 T
E)4.5 T

Question 31

A coil consists of 240 circular loops, each of radius 0.044 m, and carries a current of 2.2 A.Determine the magnetic moment of the coil.

A)0.21 A . m²
B)0.65 A . m²
C)3.2 A . m²
D)15 A . m²
E)23 A . m²

Question 32

A circular coil consists of 5 loops each of diameter 1.0 m.The coil is placed in an external magnetic field of 0.5 T.When the coil carries a current of 4.0 A, a torque of magnitude 3.93 N-m acts on it.Determine the angle between the normal to the plane of the coil and the direction of the magnetic field.

A)0°
B)30°
C)45°
D)60°
E)90°

Question 33

21-2
A long, straight, vertical segment of wire traverses a magnetic field of magnitude 2.0 T in the direction shown in the diagram.The length of the wire that lies in the magnetic field is 0.060 m.When the switch is closed, a current of 4.0 A flows through the wire from point P to point Q.
Which one of the following statements concerning the effect of the magnetic force on the wire is true?

A)The wire will be pushed to the left.
B)The wire will be pushed to the right.
C)The wire will have no net force acting on it.
D)The wire will be pushed downward, into the plane of the paper.
E)The wire will be pushed upward, out of the plane of the paper.

Question 34

A single circular loop of radius 1.00 m carries a current of 10.0 mA.It is placed in a uniform magnetic field of magnitude 0.500 T that is directed parallel to the plane of the loop as suggested in the figure.What is the magnitude of the torque exerted on the loop by the magnetic field?

A)1.57 × 10^-2 N .m
B)3.14 × 10^-2 N .m
C)6.28 × 10^-2 N . m
D)9.28 × 10^-2 N .m
E)zero N . m

Question 35

A 0.0150-m wire oriented horizontally between the poles of an electromagnet carries a direct current of 9.5 A.The angle between the direction of the current and that of the magnetic field is 25.0° as shown.If the magnetic field strength is 0.845 T, what is the magnitude and direction of the magnetic force on the wire between the poles?

A)1.17 N, upward
B)0.330 N, downward
C)0.0509 N, upward
D)0.120 N, downward
E)0.495 N, upward

Question 36

21-2
A long, straight, vertical segment of wire traverses a magnetic field of magnitude 2.0 T in the direction shown in the diagram.The length of the wire that lies in the magnetic field is 0.060 m.When the switch is closed, a current of 4.0 A flows through the wire from point P to point Q.
What is the magnitude of the magnetic force acting on the wire?

A)0.12 N
B)0.24 N
C)0.48 N
D)67 N
E)zero newtons

Question 37

21-1
A beam consisting of five types of ions labeled A, B, C, D, and E enters a region that contains a uniform magnetic field as shown in the figure below.The field is perpendicular to the plane of the paper, but its precise direction is not given.All ions in the beam travel with the same speed.The table below gives the masses and charges of the ions.Note: 1 mass unit = 1.67 × 10^-27 kg and e = 1.6 × 10^-19 C
What is the direction of the magnetic field?

A)toward the right
B)toward the left
C)into the page
D)out of the page of the page
E)toward the bottom

Question 38

21-1
A beam consisting of five types of ions labeled A, B, C, D, and E enters a region that contains a uniform magnetic field as shown in the figure below.The field is perpendicular to the plane of the paper, but its precise direction is not given.All ions in the beam travel with the same speed.The table below gives the masses and charges of the ions.Note: 1 mass unit = 1.67 × 10^-27 kg and e = 1.6 × 10^-19 C
Determine the magnitude of the magnetic field if ion A travels in a semicircular path of radius 0.50 m at a speed of 5.0 × 10⁶ m/s.

A)1.0 T
B)0.84 T
C)0.42 T
D)0.21 T
E)0.11 T

Question 39

Complete the following statement: The magnetic field around a current-carrying, circular loop is most like that of

A)the earth.
B)a short bar magnet.
C)a current-carrying, rectangular loop.
D)a long straight wire that carries a current.
E)two long straight wires that carry currents in opposite directions.

Question 40

A solenoid of length 0.250 m and radius 0.0250 m is comprised of 440 turns of wire.Determine the magnitude of the magnetic field at the center of the solenoid when it carries a current of 12.0 A.

A)2.21 × 10^-3 T
B)4.52 × 10^-3 T
C)9.05 × 10^-3 T
D)7.50 × 10^-3 T
E)zero tesla

Question 41

A coil of wire carries current I as shown in the figure.If the observer could "see" the magnetic field inside this arrangement of loops, how would it appear?

A)a
B)b
C)c
D)d
E)e

Question 42

A wire, connected to a battery and switch, passes through the center of a long current-carrying solenoid as shown in the drawing. When the switch is closed and there is a current in the wire, what happens to the portion of the wire that runs inside of the solenoid?

A)There is no effect on the wire.
B)The wire is pushed downward.
C)The wire is pushed upward.
D)The wire is pushed into the plane of the paper.
E)The wire is pushed out of the plane of the paper.

Question 43

Four long, straight wires are parallel to each other; and their cross-section forms a square.Each side of the square is 0.020 m as shown in the figure.If each wire carries a current of 8.0 A in the direction shown in the figure, determine the magnitude of the total magnetic field at P, the center of the square.

A)5.1 × 10^-5 T
B)1.1 × 10^-4 T
C)1.7 × 10^-4 T
D)2.3 × 10^-4 T
E)zero tesla

Question 44

The figure shows two concentric metal loops, each carrying a current.The larger loop carries a current of 8.0 A and has a radius of 0.060 m.The smaller loop has a radius of 0.040 m.What is the value of a current in the smaller loop that will result in zero total magnetic field at the center of the system?

A)5.3 A
B)6.0 A
C)8.8 A
D)12 A
E)24 A

Question 45

21-6
Two long, straight wires separated by 0.10 m carry currents of 18 A and 6 A in the same direction as shown.
What is the direction of the magnetic field at the point P?

A)to the left of the page
B)to the right of the page
C)toward the bottom of the page
D)out of the plane of the page
E)into the plane of the page

Question 46

21-4
A single circular loop of wire with radius 0.025 m carries a current of 6.0 A.It is placed at the center of a solenoid that has length 0.60 m, radius 0.075 m, and 1200 turns.
Determine the value of the current in the solenoid so that the magnetic field at the center of the loop is zero tesla.

A)1.4 × 10^-1 A
B)2.5 × 10^-4 A
C)6.0 × 10^-2 A
D)5.0 × 10^-3 A
E)9.3 × 10^-2 A

Question 47

21-3
A long, straight wire is carrying a current of 5.0 A in the direction shown in the figure.The point P is 0.040 m from the wire.
What is the direction of the magnetic field at point P due to the current in the wire?

A)to the right of page
B)to the left of the page
C)toward the bottom of the page
D)into the plane of the page
E)out of the plane of the page

Question 48

21-5
Two long, straight, parallel wires separated by a distance d carry currents in opposite directions as shown in the figure.The bottom wire carries a current of 6.0 A.Point C is at the midpoint between the wires and point O is a distance 0.50d below the 6-A wire as suggested in the figure.The total magnetic field at point O is zero tesla.
Determine the value of the current, I, in the top wire.

A)2 A
B)3 A
C)6 A
D)18 A
E)This cannot be determined since the value of d is not specified.

Question 49

21-6
Two long, straight wires separated by 0.10 m carry currents of 18 A and 6 A in the same direction as shown.
Determine the magnitude of the magnetic field at the point P.

A)2.4 × 10^-5 T
B)4.8 × 10^-5 T
C)7.2 × 10^-5 T
D)9.6 × 10^-5 T
E)zero tesla

Question 50

21-7
A long, coaxial cable, shown in cross-section in the drawing, is made using two conductors that share a common central axis, labeled C.The conductors are separated by an electrically insulating material that is also used as the outer cover of the cable.The current in the inner conductor is 2.0 A directed into the page and that in the outer conductor is 2.5 A directed out of the page.The distance from point C to point A is 0.0015 m; and the distance from C to B is 0.0030 m.The radii a and b of the conductors are 6.0 × 10^-4 m and 1.9 × 10^-3 m, respectively.
What is the magnitude and direction of the magnetic field at point A?

A)3.3 × 10^-5 T, clockwise
B)3.3 × 10^-5 T, counterclockwise
C)6.8 × 10^-5 T, clockwise
D)6.8 × 10^-5 T, counterclockwise
E)2.7 × 10^-4 T, clockwise

Question 51

21-4
A single circular loop of wire with radius 0.025 m carries a current of 6.0 A.It is placed at the center of a solenoid that has length 0.60 m, radius 0.075 m, and 1200 turns.
Determine the magnitude of the total magnetic field at the center of the loop (due both to the loop and the solenoid) if the current in the loop is reversed in direction from that needed to make the total field equal to zero tesla.

A)2.5 × 10^-4 T
B)3.0 × 10^-4 T
C)4.4 × 10^-4 T
D)6.7 × 10^-4 T
E)8.2 × 10^-4 T

Question 52

21-6
Two long, straight wires separated by 0.10 m carry currents of 18 A and 6 A in the same direction as shown.
Each second, 1.25 × 10¹⁹ electrons in a narrow beam pass through a small hole in a wall.The beam is perpendicular to the wall.Using Ampere's law, determine the magnitude of the magnetic field in the wall at a radius of 0.750 m from the center of the beam.

A)1.18 × 10^-9 T
B)5.34 × 10^-7 T
C)2.62 × 10^-3 T
D)4.14 × 10⁸ T
E)3.33 × 10¹² T

Question 53

21-7
A long, coaxial cable, shown in cross-section in the drawing, is made using two conductors that share a common central axis, labeled C.The conductors are separated by an electrically insulating material that is also used as the outer cover of the cable.The current in the inner conductor is 2.0 A directed into the page and that in the outer conductor is 2.5 A directed out of the page.The distance from point C to point A is 0.0015 m; and the distance from C to B is 0.0030 m.The radii a and b of the conductors are 6.0 × 10^-4 m and 1.9 × 10^-3 m, respectively.
What is the magnitude and direction of the magnetic field at point B?

A)3.3 × 10^-5 T, clockwise
B)3.3 × 10^-5 T, counterclockwise
C)6.8 × 10^-5 T, clockwise
D)6.8 × 10^-5 T, counterclockwise
E)2.7 × 10^-4 T, clockwise

Question 54

21-6
Two long, straight wires separated by 0.10 m carry currents of 18 A and 6 A in the same direction as shown.
Which one of the following materials is not ferromagnetic?

A)iron
B)chromium dioxide
C)nickel
D)aluminum
E)cobalt

Question 55

An overhead electric power line carries a maximum current of 125 A.What is the magnitude of the maximum magnetic field at a point 4.50 m directly below the power line?

A)5.56 × 10^-6 T
B)1.75 × 10^-5 T
C)3.49 × 10^-5 T
D)4.69 × 10^-4 T
E)7.95 × 10^-3 T

Question 56

Two loops carry equal currents I in the same direction.They are held in the positions shown in the figure and project above and below the plane of the paper.The point P lies exactly halfway between them on the line that joins their centers.The centers of the loops and the point P lie in the plane of the paper.Which one of the figures below shows the position of a compass needle if the compass were placed in the plane of the paper at P?

A)a
B)b
C)c
D)d
E)e

Question 57

Two loops carry equal currents I in the same direction.The loops are held in the positions shown in the figure and are then released.Which one of the following statements correctly describes the subsequent behavior of the loops?

A)Both loops move to the left.
B)The loops remain in the positions shown.
C)The top loop moves to the right; the bottom loop moves to the right.
D)The loops repel each other.
E)The loops attract each other.

Question 58

A long, straight wire carries a current I.If the magnetic field at a distance d from the wire has magnitude B, what is the magnitude of the magnetic field at a distance 2d from the wire?

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

Question 59

21-3
A long, straight wire is carrying a current of 5.0 A in the direction shown in the figure.The point P is 0.040 m from the wire.
What is the magnitude of the magnetic field at the point P?

A)1.3 × 10^-5 T
B)1.9 × 10^-5 T
C)2.5 × 10^-5 T
D)7.9 × 10^-5 T
E)9.4 × 10^-5 T

Question 60

21-5
Two long, straight, parallel wires separated by a distance d carry currents in opposite directions as shown in the figure.The bottom wire carries a current of 6.0 A.Point C is at the midpoint between the wires and point O is a distance 0.50d below the 6-A wire as suggested in the figure.The total magnetic field at point O is zero tesla.
Determine the magnitude of the magnetic field at point C if d = 0.10 m.

A)2.4 × 10^-5 T
B)4.8 × 10^-5 T
C)9.6 × 10^-5 T
D)1.1 × 10^-4 T
E)1.4 × 10^-4 T

Question 61

A wire is bent into the shape of a circle of radius r = 0.10 m and carries a 20.0-A current in the direction shown.

-Determine the magnetic moment of the loop.

A)0.20 A . m²
B)0.40 A . m²
C)0.63 A . m²
D)0.84 A . m²
E)1.3 A . m²

Question 62

21-9
A long, straight wire carries a 10.0-A current in the +y direction as shown in the figure. Next to the wire is a square copper loop that carries a 2.00-A current as shown.The length of each side of the square is 1.00 m.
What is the direction of the net magnetic force that acts on the loop?

A)+x direction
B)-x direction
C)+y direction
D)-y direction
E)30° with respect to the +x direction

Question 63

21-8
A wire is bent into the shape of a circle of radius r = 0.10 m and carries a 20.0-A current in the direction shown.
What is the direction of the magnetic field at the center of the loop?

A)to the right of the page
B)to the left of the page
C)toward the top of the page
D)into the plane of the paper
E)out of the plane of the paper

Question 64

21-8
A wire is bent into the shape of a circle of radius r = 0.10 m and carries a 20.0-A current in the direction shown.
What is the magnitude of the magnetic field at the center of the loop?

A)2.0 × 10^-5 T
B)1.3 × 10^-5 T
C)2.0 × 10^-4 T
D)1.3 × 10^-4 T
E)zero tesla

Question 65

21-7
A long, coaxial cable, shown in cross-section in the drawing, is made using two conductors that share a common central axis, labeled C.The conductors are separated by an electrically insulating material that is also used as the outer cover of the cable.The current in the inner conductor is 2.0 A directed into the page and that in the outer conductor is 2.5 A directed out of the page.The distance from point C to point A is 0.0015 m; and the distance from C to B is 0.0030 m.The radii a and b of the conductors are 6.0 × 10^-4 m and 1.9 × 10^-3 m, respectively.
A long straight wire carries a 40.0 A current in the +x direction.At a particular instant, an electron moving at 1.0 × 10⁷ m/s in the +y direction is 0.10 m from the wire.The charge on the electron is -1.6 × 10^-19 C.What is the force on the electron at this instant?

A)1.3 × 10^-16 N in the +x direction
B)1.3 × 10^-16 N in the -x direction
C)6.5 × 10^-10 N in the +y direction
D)6.5 × 10^-10 N in the -y direction
E)6.5 × 10^-16 N in the -y direction

Question 66

21-9
A long, straight wire carries a 10.0-A current in the +y direction as shown in the figure. Next to the wire is a square copper loop that carries a 2.00-A current as shown.The length of each side of the square is 1.00 m.
What is the magnitude of the net magnetic force that acts on the loop?

A)8.0 × 10^-6 N
B)1.1 × 10^-5 N
C)1.4 × 10^-5 N
D)1.7 × 10^-5 N
E)2.3 × 10^-5 N