Deck 26: The Magnetic Field

Question 1

One Tesla is equal to

A)10 G
B)100 G
C)1000 G
D)10000 G
E)10^-4 G

Answer 1

10000 G

Question 2

An electron passes through a region where there is an electric field E = 4.0 $\times$ 10⁵ V/m and a magnetic field B = 0.090 T.The directions of the electric field,the magnetic field,and the electron velocity are mutually perpendicular.If the electron is not deflected from its straight-line path through these fields,its velocity must be

A)3.6 $\times$ 10⁴ m/s
B)5.0 $\times$ 10⁵ m/s
C)2.2 $\times$ 10^-7 m/s
D)1.2 $\times$ 10⁴ m/s
E)4.4 $\times$ 10⁶ m/s

Answer 2

5.0 $\times$ 10⁵ m/s

Question 3

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

A)N · s/(C · m)
B)N · C/(s · m)
C)N · m/s²
D)C/(A · s)
E)None of these is correct.

Answer 3

N · s/(C · m)

Question 4

A deuteron is moving with a speed of 2.0 $\times$ 10⁶ m/s at right angles to a magnetic field.The field is uniform,with magnitude B = 0.40 T.The mass and charge of a deuteron are 3.3 $\times$ 10^-27 kg and 1.6 $\times$ 10^-19 C,respectively.The radius of the deuteron orbit is approximately

A)0.21 m
B)1.8 m
C)6.3 m
D)10 cm
E)27 cm

Question 5

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

A)upward.
B)downward.
C)toward the north.
D)toward the south.
E)not at all.

Question 6

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

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

Question 7

A charged particle is moving horizontally westward with a velocity of 3.5 $\times$ 10⁶ m/s in a region where there is a magnetic field of magnitude 5.6 $\times$ 10^-5 T directed vertically downward.The particle experiences a force of 7.8 $\times$ 10^-16 N northward.What is the charge on the particle?

A)+4.0 $\times$ 10^-18 C
B)-4.0 $\times$ 10^-18 C
C)+4.9 $\times$ 10^-5 C
D)-1.2 $\times$ 10^-14 C
E)+1.4 $\times$ 10^-11 C

Question 8

The radius of the orbit of an electron moving with a speed of 10⁸ m/s perpendicular to a magnetic field of 5.0 $\times$ 10^-3 T is approximately

A)1.1 m
B)0.11 m
C)0.34 m
D)0.011 m
E)8.9 m

Question 9

An electron is accelerated from rest by an electric field.After the acceleration,the electron is injected into a uniform magnetic field of 1.27 $\times$ 10^-3 T.The velocity of the electron and the magnetic field lines are perpendicular to one another.The electron remains in the magnetic field for 5.00 $\times$ 10^-9 s.The angle between the initial electron velocity and the final electron velocity is

A)1.1 rad
B)5.8 $\times$ 10^-2 rad
C)8.68 $\times$ 10^-2 rad
D)6.5 $\times$ 10^-2 rad
E)2.3 rad

Question 10

Which of the following statements is false?

A)Electric field lines due to an electric dipole and magnetic field lines due a magnetic dipole have similar configuration.
B)Electric field starts from a positive charge and ends at a negative charge.
C)Magnetic field starts at the north pole and ends at the south pole.
D)Magnetic poles always occur in pairs.
E)Magnetic fields result from the flow of charges.

Question 11

The phenomenon of magnetism is best understood in terms of

A)the existence of magnetic poles.
B)the magnetic fields associated with the movement of charged particles.
C)gravitational forces between nuclei and orbital electrons.
D)electrical fluids.
E)None of these is correct.

Question 12

A cyclotron

A)accelerates particles electrically.
B)accelerates particles magnetically.
C)guides particles magnetically.
D)gives the same period to all particles with the same charge-to-mass ratio.
E)is described by all of these.

Question 13

A wire 30 cm long with an east-west orientation carries a current of 3.0 A eastward.There is a uniform magnetic field perpendicular to this wire.If the force on the wire is 0.18 N upward,what are the direction and magnitude of the magnetic field?

A)0.20 T up
B)0.20 T north
C)0.20 T south
D)2.0 $\times$ 10^-3 T north
E)2.0 $\times$ 10^-3 T up

Question 14

The region of space around a moving proton contains

A)a gravitational field only.
B)a magnetic field only.
C)an electric field only.
D)both an electric and a magnetic field.
E)neither an electric nor a magnetic field.

Question 15

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

A)mass.
B)speed.
C)momentum.
D)energy.
E)charge-to-mass ratio.

Question 16

An electric field of 3.0 kV/m is perpendicular to a magnetic field of 0.20 T.An electron moving in a direction perpendicular to both and is not deflected if it has a velocity of

A)6 km/s
B)9 km/s
C)12 km/s
D)15 km/s
E)6.7 m/s

Question 17

The radius of curvature of the path of a charged particle moving perpendicular to a magnetic field is given by

A)qE/m
B)Bm/(qv)
C)Bv/(qm)
D)mv/(qB)
E)Bq/(mv)

Question 18

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

A)up
B)west
C)south
D)down
E)This situation cannot exist.

Question 19

A proton with a charge +e is moving with a speed v at 50º to the direction of a magnetic field .The component of the resulting force on the proton in the direction of is

A)evB sin 50º cos 50º
B)evB cos 50º
C)zero
D)evB sin 50º
E)None of these is correct.

Question 20

The radius of curvature of the path of a charged particle in a uniform magnetic field is directly proportional to

A)the particle's charge.
B)the particle's momentum.
C)the particle's energy.
D)the flux density of the field.
E)All of these are correct.

Question 21

In a mass spectrometer ions of Ni with mass 9.62 $\times$ 10^-26 kg and charge +2e are accelerated through a potential difference of X volts and then deflected in a magnetic field of 0.15 T.If the radius of curvature of the ions is 0.55 m,then calculate the value of the potential difference X.

A)5.7 kV
B)274 kV
C)137 kV
D)11.3 kV
E)none of the above

Question 22

Use the diagram for the next problem.

-A circular current loop lies in the xy plane and has radius R = 10 cm.The loop has 20 turns and carries a current I = 4 A.A magnetic field of strength 0.3 T is applied at an angle of $\theta$ = 30 ^$\circ$ to the loop.The potential energy of the magnetic dipole is

A)0.163 J
B)0.544 J
C)0.314 J
D)0.653 J
E)0.377 J

Question 23

A small permanent magnet is placed in a uniform magnetic field of magnitude 0.35 T.If the maximum torque experienced by the magnet is 0.50 N · m,what is the magnitude of the magnetic moment of the magnet?

A)1.4 A · m²
B)0.70 A · m²
C)0.18 A · m²
D)2.8 A · m²
E)0.35 A · m²

Question 24

A circular,20-turn coil has a radius of 5.0 cm.What is the magnitude of the magnetic moment of the coil when it carries a current of 2.5 A?

A)1.5 A · m²
B)0.16 A · m²
C)2.0 $\times$ 10^-2 A · m²
D)0.39 A · m²
E)3.9 kA · m²

Question 25

A beam of charged particles moving with a speed of 10⁶ m/s enters a uniform magnetic field of 0.1 T at right angles to the direction of motion.If the particles move in a radius of 0.2 m,then calculate their period of motion.

A)6.3 $\times$ 10^-7 s
B)1.3 $\times$ 10^-7 s
C)1.3 $\times$ 10^-6 s
D)4.1 $\times$ 10^-7 s
E)none of the above

Question 26

Which of the following statements correctly describes the torque-potential energy relationship for a current-carrying coil in a uniform magnetic field?

A)The maximum potential energy occurs for the same orientation of magnetic dipole and the magnetic field that corresponds to maximum torque.
B)The potential energy of the system is constant.
C)The torque rotates the coil toward a position of lower potential energy.
D)The torque rotates the coil toward a position of higher potential energy.
E)None of these is correct.

Question 27

An alpha particle with a charge 2e and mass 4m is moving with velocity v when it enters a magnetic field B at right angles to its direction of motion.A deuteron of charge e and mass 2m also enters the field in the same direction and the same speed.Calculate the difference in radius of motion between the alpha particle and the deuteron in the magnetic field region.

A)mv/eB
B)0
C)2mv/eB
D)mv/2eB
E)mv/4eB

Question 28

A circular,20-turn coil of radius 5.0 cm is oriented in such a way that its axis makes a 30º angle with a uniform magnetic field of 0.15 T.What is the torque on the coil when it carries a current of 2.5 A?

A)1.5 $\times$ 10^-3 N · m
B)9.4 $\times$ 10^-3 N · m
C)2.9 $\times$ 10^-2 N · m
D)5.1 $\times$ 10^-2 N · m
E)0.59 N · m

Question 29

When a compass needle is in stable equilibrium in a magnetic field ,

A)the needle axis is at 45º to the field.
B)the south pole points in the positive direction of .
C)the north pole points in the positive direction of .
D)the needle axis is perpendicular to .
E)none of these occurs.

Question 30

The angle through which the pointer on a galvanometer rotates is

A)proportional to the current in its coil.
B)inversely proportional to the current in its coil.
C)proportional to the magnetic flux through its coil.
D)proportional to the area of its coil.
E)independent of these factors.

Question 31

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

A)
B)
C)
D)
E)

Question 32

A beam of electrons moving at a speed of 8 $\times$ 10⁴ m/s is undeflected when it passes through an electric field of 5 N/C perpendicular to its path and a magnetic field that is perpendicular to its path and also to that of the electric field.Calculate the strength of the magnetic field.

A)1.60 $\times$ 10⁴ T
B)6.25 $\times$ 10^-5 T
C)7.81 $\times$ 10^-10 T
D)3.13 $\times$ 10^-5 T
E)1.25 $\times$ 10^-4 T

Question 33

A compass needle is in a homogeneous magnetic field with its south pole pointing in the positive direction of .The net force on the compass needle is

A)zero.
B)in the same direction as .
C)at a right angle to .
D)at right angles to the plane of and the needle.
E)in the opposite direction of .