Deck 28: Sources of Magnetic Field

Question 1

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 as the other is forced against the table's surface
B)both wires are lifted slightly
C)both wires are forced against the table's surface
D)the wires attract each other
E)the wires repel each other

Answer 1

the wires repel each other

Question 2

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

A)points up.
B)points down.
C)points toward you.
D)points away from you.
E)is zero.

Answer 2

is zero.

Question 3

Describe diamagnetism.

Answer 3

Diamagnetism is the effect of the production by a material of a magnetic field in the opposite direction to an external magnetic field that is applied to it. All materials show at least a small diamagnetic effect.

Question 4

Describe ferromagnetism.

Question 5

The ampere is defined

A)as a coulomb-second.
B)as 4π × 10^-5 SI units.
C)as a coulomb/second².
D)as 4π × 10^-7 SI units.
E)using the force between current carrying wires.

Question 6

Describe paramagnetism

Question 7

Diamond is a diamagnetic material.

Question 8

FIGURE 28-4
Fig. 28-4 shows three long, parallel, current-carrying wires. The current directions are indicated for currents I₁ and I₃. The arrow labeled F represents the magnetic force acting on current I₃. The 3 currents have equal magnitudes. What is the direction of the current I₂?

A)into the picture (in the direction opposite to that of I₁ and I₃)
B)horizontal to the right
C)vertical upward
D)vertical downward
E)out of the picture (in the same direction as I₁ and I₂)

Question 9

The magnetic field produced by a long straight current-carrying wire is

A)proportional to both the current in the wire and the distance from the wire
B)proportional to the current in the wire and inversely proportional to the distance from the wire.
C)inversely proportional to the current in the wire and proportional to the distance from the wire.
D)inversely proportional to both the current in the wire and the distance from the wire.
E)independent of both the current in the wire and the distance from the wire.

Question 10

The magnitude of the magnetic field inside a solenoid is inversely proportional to the current flowing through the solenoid.

Question 11

FIGURE 28-3
Fig. 28-3 shows three long, parallel current-carrying wires. The magnitudes of the currents are equal and their directions are indicated in the figure. Which of the arrows drawn near the wire carrying current 1 correctly indicates the direction of the magnetic force acting on that wire?

A)A
B)B
C)C
D)D
E)The magnetic force is equal to zero.

Question 12

FIGURE 28-1
Fig. 28-1 above shows two long wires carrying equal currents I₁ and I₂ flowing in opposite directions. Which of the arrows labeled A to D correctly represents the direction of the magnetic field due to the wires at a point located at an equal distance d from each wire?

A)A
B)B
C)C
D)D
E)The magnetic field is equal to zero at that point.

Question 13

FIGURE 28-2
Fig. 28-2 shows four different sets of wires that cross each other without actually touching. The magnitude of the current is the same in all four cases, and the directions of current flow are as indicated. For which configuration will the magnetic field at the center of the square formed by the wires be equal to zero?

A)A
B)B
C)C
D)D
E)The field is equal to zero in all four cases.

Question 14

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 as the other wire is forced against the table's surface.
B)both wires are lifted slightly.
C)both wires are forced against the table's surface.
D)the wires attract each other.
E)the wires repel each other.

Question 15

The magnetic field near a current carrying wire is directly proportional to the distance from the wire.

Question 16

The field outside a solenoid behaves like that of a bar magnet.

Question 17

If two identical wires carrying a certain current in the same direction are placed parallel to each other, they will experience a force of repulsion.

Question 18

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 toward you, and the wire on your left carries current away from you. From your point of view, the magnetic field at the point exactly midway between the two wires

A)points up.
B)points down.
C)points toward you.
D)points away from you.
E)is zero.

Question 19

Two parallel wires carry currents in the same direction. The direction of the force on one wire

A)is toward the other wire.
B)is perpendicular to the plane of the wires.
C)is away from the other wire.
D)is along the wire.
E)cannot be determined

Question 20

The field near a long straight wire carrying a current is inversely proportional to the current flowing through the wire.

Question 21

A small cylinder made of a diamagnetic material is brought near a bar magnet. One end of the cylinder is brought near the North pole of the magnet and is repelled. What happens when the other end of the cylinder is brought near the North pole of the magnet?

A)The other end of the cylinder will not be affected by the magnet.
B)The other end of the cylinder will be attracted less strongly by the magnet.
C)The other end of the cylinder will be attracted by the magnet.
D)The other end of the cylinder will be repelled by the magnet.
E)The other end of the cylinder will be attracted more strongly by the magnet.

Question 22

At what distance from a long straight wire carrying a current of 5.0 A is the magnitude of the magnetic field due to the wire equal to the strength of the Earth's magnetic field of about 5.0 × 10^-5 T?

A)1.0 cm
B)2.0 cm
C)3.0 cm
D)4.0 cm
E)5.0 cm

Question 23

Two long parallel wires carry currents of 20 A and 5.0 A in opposite directions. The wires are separated by 0.20 m. What is the magnetic field midway between the two wires?

A)1.0 × 10^-5 T
B)2.0 × 10^-5 T
C)3.0 × 10^-5 T
D)4.0 × 10^-5 T
E)5.0 × 10^-5 T

Question 24

In ferromagnetic materials the small regions that act like tiny magnets are called

A)conductors.
B)domains.
C)iron filings.
D)spins.
E)ferromagnets.

Question 25

A solenoid with an air core has a magnetic field pointing along its axis in the positive x direction. This solenoid is then filled with a diamagnetic material. What changes will this make to the magnetic field along the axis of the solenoid?

A)The field will point in the -x direction with a smaller magnitude.
B)The magnetic field will not change.
C)The field will point in the same direction with a larger magnitude.
D)The field will have the same magnitude but will now point in the -x direction.
E)The field will point in the same direction with a smaller magnitude.

Question 26

Two long parallel wires carry currents of 10 A in opposite directions. They are separated by 40 cm. What is the magnetic field in the plane of the wires at a point that is 20 cm from one wire and 60 cm from the other?

A)1.5 × 10^-6 T
B)3.3 × 10^-6 T
C)6.7 × 10^-6 T
D)3.3 × 10^-5 T
E)6.7 × 10^-5 T

Question 27

The magnetic permeability of a ferromagnetic material is

A)much less than μ_O.
B)slightly less than μ_O.
C)much greater than μ_O.
D)the same as μ_O.
E)slightly more than μ_O.

Question 28

The magnetic field at a distance of 2 cm from a current carrying wire is 4 μT. What is the magnetic field at a distance of 4 cm from the wire?

A)2 μT
B)4 μT
C)6 μT
D)8 μT
E)10 μT

Question 29

A piece of soft iron is placed in a solenoid increasing the magnetic field in an arrangement that can be switched on and off. Such a device is called

A)an electromagnet.
B)an electrosolenoid.
C)a permanent magnet.
D)a ferromagnet.
E)a hysteresis loop.

Question 30

FIGURE 28-5
A long straight wire carrying a 4-A current is placed along the x-axis as shown in Fig. 28-5.
(a) What is the magnitude of the magnetic field at a point P, located at y = 0.02 m, due to the current in this wire?
(b) What is the direction of the magnetic field at a point P, located at y = 0.02 m, due to this wire?

Question 31

A long wire carrying a 2.0-A current is placed along the y axis. What is the magnitude of the magnetic field at a point 0.60 m along the x-axis?

A)6.7 × 10^-7 T
B)13 × 10^-7 T
C)1.2 × 10^-7 T
D)6.7 T
E)12 T

Question 32

The magnetic field due to the current in a long, straight wire is 8.0 μT at a distance of 4.0 cm from the center of the wire. What is the current in the wire?

A)0.20 A
B)0.40 A
C)0.80 A
D)3.2 A
E)1.6 A

Question 33

How do paramagnetic materials differ from diamagnetic materials?

A)They are the same.
B)Paramagnetic molecules are metallic.
C)Paramagnetic molecules don't have a permanent dipole moment.
D)Paramagnetic molecules have a permanent dipole moment.
E)Paramagnetic molecules are non-metallic.

Question 34

The magnetic field due to a 2-A current flowing in a long, straight wire is 8 μT at a point P, a certain distance away from the wire. How far is this point from the center of the wire?

A)2 cm
B)3 cm
C)4 cm
D)5 cm
E)6 cm

Question 35

The magnitude of the magnetic field 8.0 cm from a straight wire carrying a current of 6.0 A is

A)1.5 × 10^-3 T.
B)1.5 × 10^-5 T.
C)3.0 × 10^-3 T.
D)3.0 π × 10^-4 T.
E)3.0 × 10^-5 T.

Question 36

Ferromagnetic materials lose their ability to form permanent magnets if

A)aligned north and south.
B)heated above their Curie temperature.
C)cooled below their Curie temperature.
D)the electrons lose their spin magnetic moment.
E)aligned east and west.

Question 37

A high power line carrying 1000 A generates what magnetic field at the ground, 10 m away?

A)3.2 × 10^-6 T
B)4.7 × 10^-6 T
C)6.4 × 10^-6 T
D)2.0 × 10^-5 T
E)5.6 × 10^-5 T

Question 38

The coulomb is the same as

A)T∙A/m.
B)A∙s.
C)A/s.
D)all of the above
E)none of the above

Question 39

Which of the solenoids described below has the greatest magnetic field along its axis?

A)a solenoid of length L, with N turns and a current I
B)a solenoid of length L, with N/2 turns and a current I
C)a solenoid of length L/2, with N/2 turns and a current I
D)a solenoid of length 2L, with N turns and a current I/2
E)a solenoid of length 2L, with 2N turns and a current 2I

Question 40

In using Ampere's law, the integral must be evaluated

A)around a path that lies in a plane.
B)in a clockwise direction.
C)around a closed path.
D)around a circular path.
E)in a counter-clockwise direction.

Question 41

Two long parallel wires carry currents of 5.0 A and 8.0 A in the opposite direction. The wires are separated by 0.30 m. Find the magnetic force per unit length between the two wires.

A)2.7 × 10^-5 N/m repulsive
B)7.2 × 10^-5 N/m repulsive
C)3.4 × 10^-5 N/m attractive
D)2.7 × 10^-5 N/m attractive
E)7.2 × 10^-5 N/m attractive

Question 42

A straight wire carries a 12-A current eastward and a second straight wire carries a 14-A current westward. The wires are separated by a distance of 42 cm. The force per unit length on the wire carrying 12 A is

A)8.0 × 10^-5 N/m.
B)5.1 × 10^-7 N/m.
C)5.1 × 10^-4 N/m.
D)5.1 × 10^-6 N/m.
E)8.0 × 10^-7 N/m.

Question 43

A solenoid of 200 turns carrying a current of 2 A has a length of 25 cm. What is the magnitude of the magnetic field at the center of the solenoid?

A)2 mT
B)3 mT
C)4 mT
D)5 mT
E)6 mT

Question 44

How much current must pass through a 400 turn coil 4.0 cm long to generate a 1.0-T magnetic field at the center?

A)0.013 A
B)13 A
C)22 A
D)40 A
E)80 A

Question 45

FIGURE 28-7
Two parallel segments of wire, of length L = 0.8m are positioned a distance d = 1 m apart as shown in Fig. 28-7. Calculate the magnetic field at point P located half-way between the two segments. (Each segment carries and electric current I = 10 A in the directions indicated.)

A)8 μT
B)3 μT
C)1 μT
D)0.5μT
E)0

Question 46

FIGURE 28-9
Fig. 28-9 shows a segment of wire of length L = 0.5 m, carrying a current I = 20 A. Calculate the magnitude of the magnetic field produced by this wire at a point P located at a distance D = 1.0 m from one of the ends of the wire.

A)0.8 × 10^-7 T
B)5.8 × 10^-7 T
C)2.1 × 10^-7 T
D)6.3 × 10^-7 T
E)8.9 × 10^-7 T

Question 47

A circular loop of wire of radius 10 cm carries a current of 6A. The magnitude of the magnetic field at the center of the loop is

A)3.8 × 10^-5 T.
B)3.8 × 10^-7 T.
C)1.2 × 10^-5 T.
D)1.2 × 10^-7 T.
E)3.8 × 10^-8 T.

Question 48

FIGURE 28-8
Fig. 28-8 shows the cross-section of a hollow cylinder of inner radius a = 5 cm and outer radius b = 7 cm. A uniform current density j = 1 A/ cm² flows through the cylinder. Calculate the magnitude of the magnetic field at a distance d = 10 cm from the axis of the cylinder.

A)0
B)1.5 × 10^-4 T
C)2.5 × 10^-4 T
D)4.5 × 10^-4 T
E)0.5 × 10^-4 T

Question 49

What is the value of the magnetic field at the center of a square wire of length a on the side, if the current in the wire is I?

A)B =
B)B =
C)B =
D)B =
E)B = 0

Question 50

A toroidal solenoid has a radius R = 0.5 m and a cross-sectional diameter equal to 10 cm. When a current I passes through the coil of the solenoid, the magnetic field at the center of the solenoid has a magnitude B = 2 μT. What is the largest value of the magnetic field in the solenoid for the same value of the current?

A)3.5 μT
B)1.8 μT
C)2.2 μT
D)0.5 μT
E)2.8 μT

Question 51

A semicircular wire of radius R connects two straight wire segments. If a current I flows along the wire, the magnitude of the magnetic field at the center of the semicircular wire due to the current in the semicircular wire is

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

Question 52

A wire of thickness d = 5 mm is tightly wound 200 times around a cylindrical core to form a solenoid. A current I = 0.1 A is sent through the wire. What is the the magnetic field on the axis of the solenoid?

A)6.6 × 10^-5 T
B)2.5 × 10^-5 T
C)1.3 × 10^-5 T
D)3.6 × 10^-5 T
E)9.8 × 10^-5 T

Question 53

A solenoid with a certain number of turns N and carrying a current of 2.000 A has a length of 34.00 cm. If the magnitude of the magnetic field generated at the center of the solenoid is 9.000 mT, what is the value of N?

A)860.0
B)1591
C)2318
D)3183
E)1218

Question 54

A solenoid with 400 turns has a radius of 0.040 m and is 40 cm long. If this solenoid carries a current of 12 A, what is the magnitude of the magnetic field at the center of the solenoid?

A)16 mT
B)4.9 mT
C)15 mT
D)6.0 mT
E)9.0 mT

Question 55

FIGURE 28-10
Two coaxial circular coils of radius R = 15 cm are positioned a distance d = 20 cm apart, as shown in Fig. 28-10. Calculate the magnetic field half-way between the coils. Each coil carries a current I = 4 A.

A)0.9 × 10^-3 T
B)3.9 × 10^-3 T
C)1.9 × 10^-3 T
D)6.3 × 10^-3 T
E)9.2 × 10^-3 T

Question 56

A straight wire carries a 12-A current eastward and a second straight wire carries a 14-A current westward. The wires are separated by a distance of 42 cm. The force on a 6.4 m length of one of the wires is

A)8.0 × 10^-7 N.
B)5.1 × 10^-4 N.
C)8.0 × 10^-5 N.
D)5.1 × 10^-6 N.
E)not possible to determine with the information given.

Question 57

How many turns should a 10-cm long solenoid have if it is to generate a 1.5 × 10^-3 T magnetic field on 1.0 A of current?

A)12
B)15
C)120
D)1200
E)3200

Question 58

A 1000-turn toroid has a central radius of 4.2 cm and is carrying a current of 1.7 A. The magnitude of the magnetic field along the central radius is

A)8.1 × 10^-3 T.
B)5.1 × 10^-2 T.
C)1.6 × 10^-2 T.
D)8.1 × 10^-2 T.
E)0.

Question 59

FIGURE 28-6
Fig. 28-6 shows two long, parallel current-carrying wires. The wires carry equal currents = = 20 A in the directions indicated and are located a distance d = 0.5 m apart. Calculate the magnitude and direction of the magnetic field at a point located at an equal distance d from each wire.

A)8μT downward
B)8μT upward
C)4μT downward
D)4μT upward
E)4μT to the right

Question 60

Four long parallel wires each carry 2.0 A in the same direction. They are parallel to the z-axis, and they pass through the corners of a square of side 4.0 cm positioned in the x-y plane. What magnetic field does one of the wires experience due to the other wires?

A)1.2 × 10^-6 T
B)2.1 × 10^-6 T
C)1.2 × 10^-5 T
D)2.7 × 10^-5 T
E)0 T

Question 61

A solenoid with n₁ = 1200 turns/m and a current I₁ = 2.5 A is filled with a paramagnetic material at a temperature T₁ = 320 K. A second solenoid with n₂ = 1000 turns/m and a current I₂ = 0.85 A is filled with the same paramagnetic material at a different temperature T₂. The magnetizations are the same in both cases. What is the value of T₂?

A)256 K
B)150 K
C)67 K
D)91 K
E)201 K

Question 62

The core of a long solenoid with 1000 turns/m and a current of 0. 5 A is filled with an unknown material. It is found that the magnetic field along the axis of the solenoid increases by 0.0017%. What is the magnetic susceptibility of the unknown material?

A)1.7 × 10^-5
B)3.4 × 10^-5
C)0.0048
D)-3.4 × 10^-5
E)0.0021

Question 63

Aluminum has a magnetic susceptibility χ = 1.7 × 10^-5 at T = 300 K. What will be the magnetization of a small sample of aluminum placed in a 1.5 T magnetic field at T = 150 K?

A)20.3 A/m
B)1.5 A/m
C)81.1 A/m
D)40.6 A/m
E)10.2 A/m