Deck 19: Magnetism Magnets

Question 1

A proton moving at a speed of 3.2 × 10⁶ m/s cuts across the lines of a magnetic field at an angle of 61°.The strength of the field is 0.63 × 10−⁴ T.What is the magnitude of the force acting on the proton? (q_p = 1.6 × 10−¹⁹ C)

A) 1.6E-17 N
B) 3.1E-17 N
C) 2.8E-17 N
D) 7.1E-9 N
E) ​4.5E-36 N

Answer 1

2.8E-17 N

Question 2

A soft magnetic material has which property?

A) It cannot be magnetized.
B) It is easy to magnetize.
C) It is hard to magnetize.
D) It attracts slowly moving charges.

Answer 2

It is easy to magnetize.

Question 3

The magnetic field of the Earth is believed responsible for which of the following?

A) deflection of both charged and uncharged cosmic rays
B) deflection of charged cosmic rays
C) ozone in the upper atmosphere
D) solar flares

Answer 3

deflection of charged cosmic rays

Question 4

Different units can be used to measure the same physical quantity,differing only by some multiplicative factor.The cgs unit for magnetic field,the gauss,is equal to ________ tesla.

A) 10⁴
B) 10^-4
C) 0.5
D) These units do not measure the same physical quantity.

Question 5

If a proton is released at the equator and falls toward the Earth under the influence of gravity,the magnetic force on the proton will be toward the:

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

Question 6

The force on a charged particle created by its motion in a magnetic field is maximum at what angle between the particle velocity and field?

A) zero
B) 180°
C) 90°
D) 45°

Question 7

The right-hand rule allows one to find a property of the interaction of a magnetic field with a charged particle.The right-hand rule applied to moving charges:

A) results in positive charges moving clockwise.
B) results in negative charges moving clockwise.
C) can be used for positive charges only.
D) gives the direction of the force on a charge moving in a magnetic field.

Question 8

A proton is released such that its initial velocity is from right to left across this page.The proton's path,however,is deflected in a direction toward the bottom edge of the page due to the presence of a uniform magnetic field.What is the direction of this field?

A) out of the page
B) into the page
C) from bottom edge to top edge of the page
D) from right to left across the page

Question 9

A proton moves across the Earth's equator in a northeasterly direction.At this point the Earth's magnetic field has a direction due north and is parallel to the surface.What is the direction of the force acting on the proton at this instant?

A) toward the northwest
B) out of the Earth's surface
C) into the Earth's surface
D) toward the northeast

Question 10

A proton is released such that it has an initial speed of 3.7 × 10⁵ m/s from left to right across the page.A magnetic field of 1.5 T is present at an angle of 18° to the horizontal direction (or positive x axis).What is the magnitude of the force experienced by the proton? (q_p = 1.6 × 10−¹⁹ C)

A) 4.4E-33 N
B) 2.0E-33 N
C) 2.7E-14 N
D) 6.7E-14 N
E) ​8.4E-14 N

Question 11

The magnetic pole of the Earth nearest the geographic North Pole corresponds to which of the following?

A) a magnetic north pole
B) a magnetic south pole
C) a magnetic arctic pole
D) a magnetic Antarctic pole

Question 12

Assume that a uniform magnetic field is directed into this page.If an electron is released with an initial velocity directed from the bottom edge to the top edge of the page,which of the following describes the direction of the resultant force acting on the electron?

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

Question 13

An electron which moves with a speed of 2.5 × 10⁴ m/s parallel to a uniform magnetic field of 0.44 T experiences a force of what magnitude? (e = 1.6 × 10−¹⁹ C)

A) 1.76E-15 N
B) 2.82E-33 N
C) 8.80E-16 N
D) 9.09E-15 N
E) zero

Question 14

A stationary positive charge +Q is located in a magnetic field B,which is directed toward the right as indicated.The direction of the magnetic force on Q is:

A) toward the right.
B) up.
C) down.
D) There is no magnetic force.

Question 15

Electrical charges and magnetic poles have many similarities,but one difference is:

A) opposite magnetic poles repel.
B) one magnetic pole cannot create magnetic poles in other materials.
C) a magnetic pole cannot be isolated.
D) magnetic poles do not produce magnetic fields.

Question 16

The dip angle is:

A) another term for magnetic declination.
B) a measure of the tendency for a compass to point south.
C) close to or at zero near the equator.
D) close to or at zero just north of Hudson Bay.

Question 17

Geophysicists today generally attribute the existence of the Earth's magnetic field to which of the following?

A) convection currents within the liquid interior
B) iron ore deposits in the crust
C) nickel-iron deposits in the crust
D) solar flares

Question 18

The term magnetic declination refers to which of the following?

A) angle between Earth's magnetic field and Earth's surface
B) Earth's magnetic field strength at the equator
C) tendency for Earth's field to reverse itself
D) angle between directions to true north and magnetic north

Question 19

Which of the following is not a hard magnetic material?

A) iron
B) cobalt
C) nickel
D) both b and c

Question 20

Which of the following locations has the smallest (in magnitude)magnetic declination?

A) Washington state
B) the South Carolina - Georgia border
C) the San Francisco - Oakland area
D) western Colorado

Question 21

The force exerted on a current-carrying wire located in an external magnetic field is directly proportional to which of the following?

A) current strength
B) field strength
C) both A and B
D) None of the above are valid.

Question 22

A 1.0-m wire segment carrying a current of 0.88 A oriented parallel to a uniform magnetic field of 0.62 T experiences a force of what magnitude?

A) 0.55 N
B) 0.27 N
C) 0.87 N
D) 0.44 N
E) zero

Question 23

A circular loop carrying a current of 1.2 A is oriented in a magnetic field of 0.23 T.The loop has an area of 0.16 m² and is mounted on an axis,perpendicular to the magnetic field,which allows the loop to rotate.What is the torque on the loop when its plane is oriented at a 34° angle to the field?

A) 0.025 N⋅m
B) 0.037 N⋅m
C) 0.037 N⋅m.
D) 0.023 N⋅m
E) ​0.96 N⋅m

Question 24

The direction of the force on a current carrying wire located in an external magnetic field is which of the following?

A) perpendicular to the current
B) perpendicular to the field
C) Both choices A and B are valid.
D) None of the above are valid.

Question 25

A circular current loop is placed in an external magnetic field.How is the torque related to the radius of the loop?

A) directly proportional to radius
B) inversely proportional to radius
C) directly proportional to radius squared
D) inversely proportional to radius squared

Question 26

A horizontal wire of length 4.3 m carries a current of 6.2 A and is oriented so that the current direction is 75° S of W.The Earth's magnetic field is due north at this point and has a strength of 0.14 × 10−⁴ T.What is the size of the force on the wire?

A) 3.6 × 10−⁴ N
B) 3.4 × 10−⁴ N
C) 1.4 × 10−⁴ N
D) 1.0 × 10−⁴ N
E) ​3.7 × 10−³ N

Question 27

A current-carrying wire of length 42 cm is positioned perpendicular to a uniform magnetic field.If the current is 6.7 A and it is determined that there is a resultant force of 2.9 N on the wire due to the interaction of the current and field,what is the magnetic field strength?

A) 1.03 T
B) 0.10 T
C) 0.15 T
D) 3.7E-3 T
E) ​1.8E-3 T

Question 28

A rectangular coil (0.12 m × 0.82 m)has 194 turns and is in a uniform magnetic field of 0.44 T.If the orientation of the coil is varied through all possible positions,the maximum torque on the coil by magnetic forces is 0.060 N⋅m.What is the current in the coil?

A) 0.75 mA
B) 1.4 A
C) 7.1 mA
D) 2.7 A
E) ​0.07 A

Question 29

There is a magnetic force on a particle.It is possible that the particle is:

A) uncharged.
B) stationary.
C) moving in the direction of the magnetic field.
D) not part of a wire.

Question 30

A proton and a deuteron are moving with equal velocities perpendicular to a uniform magnetic field.A deuteron has the same charge as the proton but has twice its mass.The ratio of the acceleration of the proton to that of the deuteron is:

A) 0.5.
B) 1.
C) 2.
D) There is no acceleration in this case.

Question 31

A circular loop carrying a current of 1.6 A is oriented in a magnetic field of 0.28 T.The loop has an area of 0.22 m² and is mounted on an axis,perpendicular to the magnetic field,which allows the loop to rotate.If the plane of the loop is oriented parallel to the field,what torque is created by the interaction of the loop current and the field?

A) 0.04 N⋅m
B) 0.16 N⋅m
C) 0.10 N⋅m
D) 0.049 N⋅m
E) ​0.028 N⋅m

Question 32

Which of the following devices makes use of an electromagnet?

A) loudspeaker
B) galvanometer
C) both A and B
D) None of the above.

Question 33

There is a current I flowing in a clockwise direction in a square loop of wire that is in the plane of the paper.If the magnetic field B is toward the right,and if each side of the loop has length L,then the net magnetic torque acting on the loop is:

A) 2ILB.
B) ILB.
C) IBL².
D) zero.

Question 34

A horizontal wire of length 3.0 m carries a current of 6.0 A and is oriented so that the current direction is 50° S of W.The Earth's magnetic field is due north at this point and has a strength of 0.14 × 10−⁴ T.What is the direction of the force on the wire?

A) out of the Earth's surface
B) toward the Earth's surface
C) due east
D) 40° S of E

Question 35

A proton and a deuteron are moving with equal velocities perpendicular to a uniform magnetic field.A deuteron has the same charge as the proton but has twice its mass.The ratio of the magnetic force on the proton to that on the deuteron is:

A) 0.5.
B) 1.
C) 2.
D) There is no magnetic force in this case.

Question 36

An electron moves through a region of crossed electric and magnetic fields.The electric field E = 3381 V/m and is directed straight down.The magnetic field B = 0.77 T and is directed to the left.For what velocity v of the electron into the paper will the electric force exactly cancel the magnetic force?

A) 4400 m/s
B) 2600 m/s
C) 4200 m/s
D) 5200 m/s
E) ​7000 m/s

Question 37

A wire is lying horizontally in the north-south direction and the horizontal magnetic field is toward the east.Some positive charges in the wire move north and an equal number of negative charges move south.The direction of the force on the wire will be:

A) east.
B) down,into the page.
C) up,out of the page.
D) There is no magnetic force.

Question 38

A circular coil (radius = 0.54 m)has 163 turns and is in a uniform magnetic field.If the orientation of the coil is varied through all possible positions,the maximum torque on the coil by magnetic forces is 0.19 N⋅m when the current in the coil is 2.1 mA.What is the magnitude of the magnetic field?

A) 1.9 T
B) 0.05 T
C) 0.61 T
D) 53 T
E) ​0.99 T

Question 39

A copper wire of length 11 cm is in a magnetic field of 0.42 T.If it has a mass of 19 g,what is the minimum current through the wire that would cause a magnetic force equal to its weight?

A) 41 A
B) 3.7 A
C) 4.0 A
D) 9.6 A
E) ​2.5 A

Question 40

There is a current I flowing in a clockwise direction in a square loop of wire that is in the plane of the paper.If the magnetic field B is toward the right,and if each side of the loop has length L,then the net magnetic force acting on the loop is:

A) 2ILB.
B) ILB.
C) IBL².
D) zero.

Question 41

Two singly ionized isotopes,X and Y,of the same element move with the same speed perpendicular to a uniform magnetic field.Isotope X follows a path of radius 3.29 cm while isotope Y moves along a path 3.43 cm in radius.What is the ratio of the two isotope masses,

A) 0.959
B) 1.04
C) 0.920
D) 1.09
E) ​Not enough information is given.

Question 42

When a magnetic field causes a charged particle to move in a circular path,the only quantity listed below which the magnetic force changes significantly as the particle goes around in a circle is the particle's:

A) energy.
B) momentum.
C) radius for the circle.
D) time to go around the circle once.

Question 43

A proton,which moves perpendicular to a magnetic field of 0.8 T in a circular path of radius 0.062 m,has what speed? (q_p = 1.6 × 10−¹⁹ C and m_p = 1.67 × 10−²⁷ kg)

A) 2.9E+5 m/s
B) 1.3E+7 m/s
C) 7.4E+6 m/s
D) 4.8E+6 m/s
E) ​1.9E+6 m/s

Question 44

A deuteron,with the same charge but twice the mass of a proton,moves with a speed of 1.7 × 10⁵ m/s perpendicular to a uniform magnetic field of 0.36 T.Which of the paths described below would it follow? (q_p = 1.6 × 10−¹⁹ C and m_d = 3.34 × 10−²⁷ kg)

A) a straight line path
B) a circular path of 2.5 cm radius
C) a circular path of 1.0 cm radius
D) a circular path of 0.09 cm radius
E) ​a circular path of 0.87 cm radius

Question 45

A proton,mass 1.67 × 10−²⁷ kg and charge +1.6 × 10−¹⁹ C,moves in a circular orbit perpendicular to a uniform magnetic field of 0.66 T.Find the time for the proton to make one complete circular orbit.

A) 3.2 × 10−⁸ s
B) 9.9 × 10−⁸ s
C) 5.0 × 10−⁸ s
D) 1.6 × 10−⁸ s
E) ​Not enough information is given.

Question 46

The path of a charged particle moving parallel to a uniform magnetic field will be a:

A) straight line.
B) circle.
C) ellipse.
D) parabola.

Question 47

A current in a long,straight wire produces a magnetic field.The magnetic field lines:

A) go out from the wire to infinity.
B) come in from infinity to the wire.
C) form circles that pass through the wire.
D) form circles that go around the wire.

Question 48

In a mass spectrometer,an ion will have a smaller radius for its circular path if:

A) its speed is greater.
B) its mass is greater.
C) its charge is greater.
D) the magnetic field is weaker.

Question 49

An electron is moving at a speed of 5.1 × 10⁶ m/s at an angle of 23° with respect to a uniform magnetic field of 7.3 × 10^-4 T.What is the radius of the resulting helical path? (m_e = 9.11 × 10^-31 kg,q_e = 1.6 × 10^-19 C)

A) 3.7 cm
B) 4.0 cm
C) 3.2 cm
D) 1.6 cm
E) ​3.4 cm

Question 50

A 71-m-long wire carrying a current of 4.9 A will be accompanied by a magnetic field of what strength at a distance of 0.090 m from the wire? (magnetic permeability in empty space µ₀ = 4π × 10−⁷ T⋅m/A)

A) 3.4 × 10−⁵ T
B) 0.69 × 10−⁵ T
C) 1.1 × 10−⁵ T
D) 0.54 × 10−⁵ T
E) ​zero

Question 51

A proton moving with a speed of 2.9 × 10⁵ m/s perpendicular to a uniform magnetic field of 0.35 T will follow which of the paths described below? (q_p = 1.6 × 10−¹⁹ C and m_p = 1.67 × 10−²⁷ kg)

A) a straight line path
B) a circular path of 0.9 cm radius
C) a circular path of 2.2 cm radius
D) a circular path of 0.31 cm radius
E) ​a circular path of 2.5 cm radius

Question 52

At the Fermilab accelerator in Weston,Illinois,singly-charged ions with momentum 4.8 × 10−¹⁶ kg⋅m/s are held in a circular orbit of radius 0.8 km by an upward magnetic field.What B-field must be used to maintain the ions in this orbit? (qion = 1.6 × 10−¹⁹ C)

A) 9.6 T
B) 2.4 T
C) 3.8 T
D) 0.16 T
E) ​0.27 T

Question 53

A proton with initial kinetic energy E is moving in circular motion in a uniform magnetic field.When it has completed one eighth of a revolution,what is its kinetic energy?

A) 1.4 E
B) 0.71 E
C) E
D) The value is not given.

Question 54

If a charged particle is moving in a uniform magnetic field,its path can be:

A) a straight line.
B) a circle.
C) a helix.
D) any of the above.

Question 55

A high-voltage power line 26.9 m above the ground carries a current of 2722 A.What is the magnetic field due to the current directly underneath the power line? (µ₀ = 4π × 10−⁷ T⋅m/A)

A) 20.2 µT
B) 63.6 µT
C) 64.4 mT
D) 12.7 mT
E) ​12.7 T

Question 56

The current in a long wire creates a magnetic field in the region around the wire.How is the strength of the field at distance r from the wire center related to the magnitude of the field?

A) field directly proportional to r
B) field inversely proportional to r
C) field directly proportional to r²
D) field inversely proportional to r²

Question 57

Two long parallel wires 10 cm apart carry currents of 4.2 A and 8.7 A in the same direction.Is there any point between the two wires where the magnetic field is zero?

A) yes,midway between the wires
B) yes,6.7 cm from the 4.2-A wire
C) yes,3.3 cm from the 4.2-A wire
D) yes,3.3 cm from the 8.7-A wire
E) ​no.

Question 58

A superconducting wire carries a current of 10 kA.Find the magnetic field at a distance of 2.0 m from the wire.(µ₀ = 4π × 10−⁷ T⋅m/A)

A) 1.0 × 10−³ T
B) 0.32 × 10−³ T
C) 3.1 × 10−² T
D) 1.6 × 10−² T
E) ​6.3 × 10−³ T

Question 59

Magnetism had been a known phenomenon for some time before its relation to electric currents was found.That a current in a wire produces a magnetic field was discovered by:

A) Maxwell.
B) Ampere.
C) Oersted.
D) Tesla.

Question 60

An incredible amount of electrical energy passes down the funnel of a large tornado every second.Measurements at a distance of 11.95 km from a large tornado showed an almost constant magnetic field of 2.69 × 10−⁸ T associated with the tornado.What was the average current going down the funnel? (µ₀ = 4π × 10−⁷ T⋅m/A)

A) 3220 A
B) 1607 A
C) 804 A
D) 1023 A
E) ​5050 A

Question 61

Two parallel conductors each of 0.67 m length,separated by 4.1 × 10−³ m and carrying 3.2 A in opposite directions,will experience what type and magnitude of mutual force? (magnetic permeability in empty space µ₀ = 4π × 10−⁷ T⋅m/A)

A) attractive,7.5 × 10−⁴ N
B) repulsive,7.5 × 10−⁴ N
C) attractive,3.3 × 10−⁴ N
D) repulsive,3.3 × 10−⁴ N
E) ​zero

Question 62

Superconductors can carry very large currents with no resistance.If a superconducting wire is formed into a solenoid of length 74.6 cm with 660 turns,what is the magnetic field inside the solenoid when the current is 6.5 kA? (µ₀ = 4π × 10−⁷ T⋅m/A)

A) 0.58 T
B) 4.02 T
C) 14.5 T
D) 7.23 T
E) ​22.7 T

Question 63

Two long parallel wires 32.7 cm apart are carrying currents of 5.9 A and 28.5 A in the same direction.What is the magnitude of the magnetic field halfway between the wires?

A) 2.8 × 10^-5 T
B) 4.2 × 10^-5 T
C) 0.7 × 10^-5 T
D) 3.5 × 10^-5 T
E) ​1.4 × 10^-5 T

Question 64

Two parallel wires carry the a current I in the same direction.Midway between these wires is a third wire,also parallel to the other two,which carries a current 0.5 I,but in the direction opposite from the first two wires.In which direction are the net forces on the outer wires?

A) Since the net forces are zero,there is no direction.
B) Both forces are toward the center wire.
C) Both forces are away from the center wire.
D) Both forces on the two wires are in the same direction in space.

Question 65

A superconducting solenoid is to be designed to generate a magnetic field of 6.10 T.If the solenoid winding has 969 turns/m,what is the required current? (µ₀ = 4π × 10−⁷ T⋅m/A)

A) 2510 A
B) 1600 A
C) 5010 A
D) 800 A
E) ​140 A

Question 66

When an electromagnet has an iron core inserted,what happens to the strength of the magnet?

A) It increases.
B) It remains the same.
C) It decreases.
D) Since it depends on the metal used in the wires of the electromagnet,any of the above.

Question 67

Two insulated current-carrying straight wires of equal length are arranged in the lab so that Wire A carries a current northward and Wire B carries a current eastward,the wires crossing at their midpoints separated only by their insulation.Which of the following statements are true?

A) The net force on Wire B is southward.
B) The net force on Wire A is westward.
C) There are no forces in this situation.
D) There are forces,but the net force on each wire is zero.

Question 68

The magnetic domains in a non-magnetized piece of iron are characterized by which orientation?

A) parallel to the magnetic axis
B) anti-parallel (opposite direction)to the magnetic axis
C) random
D) perpendicular to the magnetic axis

Question 69

Consider two long,straight parallel wires,each carrying a current I.If the currents are flowing in opposite directions:

A) the two wires will attract each other.
B) the two wires will repel each other.
C) the two wires will exert a torque on each other.
D) neither wire will exert a force on the other.

Question 70

Niobium metal becomes a superconductor (with electrical resistance equal to zero)when cooled below 9 K.If superconductivity is destroyed when the surface magnetic field exceeds 0.100 T,determine the maximum current a 3.43-mm-diameter niobium wire can carry and remain superconducting.(µ₀ = 4π × 10−⁷ T⋅m/A)

A) 1720 A
B) 273 A
C) 136 A
D) 860 A
E) ​2690 A

Question 71

A square coil and a triangular coil each have sides of length L.The triangular coil has twice as many turns as the square coil.If a the same current is sent through each coil,when the coils are placed in the same uniform magnetic field making an angle of 30^° with the planes of the coils,which coil experiences the greater torque?

A) the square coil
B) the triangular coil
C) Both coils experience the same torque.
D) It depends on the magnitude of the magnetic field that the coils are placed in.

Question 72

Square coil A has 2N turns and sides of length L,and square coil B has N turns and sides of length 2L.When a current of 2 amps is sent through coil A and a current of 1 amp is sent through coil B,which coil has the greater magnetic moment?

A) coil A
B) coil B
C) Both have the same magnetic moment.
D) More information is needed.

Question 73

Two parallel wires are separated by 0.43 m.Wire A carries 3.3 A and Wire B carries 8.3 A,both currents in the same direction.The force on 0.90 m of Wire A is:

A) 1.1 × 10^-5 N.
B) 1.4 × 10^-5 N.
C) 0.35 × 10^-5 N.
D) 0.14 × 10^-5 N.
E) ​3.6 × 10^-5 N.

Question 74

A current in a solenoid coil creates a magnetic field inside that coil.The field strength is directly proportional to:

A) the coil area.
B) the current.
C) Both A and B are valid choices.
D) None of the above choices are valid.

Question 75

Two parallel conductors are carrying currents in the same direction.The currents are non-zero and not necessarily equal.The magnitude of the magnetic field midway between them is 40 μT.If one of the currents then has its direction reversed,what is the resulting magnitude of the magnetic field midway between them?

A) a value greater than 40 μT
B) 40 μT
C) a value less than 40 μT
D) It could be any value.

Question 76

Two parallel conductors are carrying currents in the opposite direction.The currents are non-zero and not necessarily equal.The magnitude of the magnetic field midway between them is 40 μT.If one of the currents then has its direction reversed,what is the resulting magnitude of the magnetic field midway between them?

A) a value greater than 40 μT
B) 40 μT
C) a value less than 40 μT
D) It could be any value.

Question 77

Two long parallel wires 45.3 cm apart are carrying currents of 10.3 A and 29.8 A in the opposite direction.What is the magnitude of the magnetic field halfway between the wires?

A) 1.72 × 10^-5 T
B) 0.91 × 10^-5 T
C) 3.54 × 10^-5 T
D) 2.63 × 10^-5 T
E) ​1.77 × 10^-5 T

Question 78

A solenoid with 338 turns,0.28 m long,carrying a current of 2.6 A and with a radius of 10−² m will have what strength magnetic field at its center? (magnetic permeability in empty space µ₀ = 4π × 10−⁷ T⋅m/A)

A) 5.5E-2 T
B) 9.9E-4 T
C) 1.1E-3 T
D) 3.9E-3 T
E) ​1.2E-2 T

Question 79

A current in a solenoid with N turns creates a magnetic field at the center of that loop.The field strength is directly proportional to:

A) number of turns in the loop.
B) current strength.
C) Both choices A and B are valid.
D) None of the above are valid.

Question 80

Two parallel wires are separated by 0.25 m.Wire A carries 5.0 A and Wire B carries 10 A,both currents in the same direction.The force on 0.80 m of Wire A is:

A) half that on 0.80 m of wire B.
B) one-fourth that on 0.80 m of wire B.
C) toward Wire B.
D) away from Wire B.