Multiple Choice
Identify the
letter of the choice that best completes the statement or answers the question.
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1.
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A
charged particle is moving horizontally westward with a velocity of 3.5 ´ 106
m/s in a region where there is a magnetic field of magnitude 5.6 ´
10–5 T directed vertically downward. The particle experiences a force of 7.8
´
10–16 N northward. What is the charge on the particle? a. | +4.0
´
10–18 C | b. | –4.0 ´ 10–18 C | c. | +4.9
´
10–5 C | d. | –1.2 ´ 10–14 C | e. | +1.4
´
10–11 C | | |
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2.
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A
proton with a charge +e is moving with a speed v at 50º to the direction of a
magnetic field B. The component of the resulting force on the proton in the
direction of B is a. | evB sin 50º cos 50º | b. | evB cos
50º | c. | zero | d. | evB sin 50º | e. | None of these is
correct. | | |
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3.
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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 ´
10–3 T north | e. | 2.0 ´ 10–3 T up | | |
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4.
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An
electron is traveling horizontally east in the magnetic field of the earth near the equator.
The direction of the force on the electron is a. | zero | b. | north | c. | south | d. | upward | e. | downward | | |
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5.
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A
rectangular loop of wire (0.10 m by 0.20 m) carries a current of 5.0 A in a counterclockwise
direction. The loop is oriented as shown in a uniform magnetic field of 1.5 T. The force
acting on the upper 0.10-m side of the loop is a. | 1.5 N | b. | 0.75
N | c. | 0.50
N | d. | 0.15
N | e. | zero | | |
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6.
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A
positively charged particle moves with velocity vT along the x axis. A uniform magnetic field
–BB exists in the negative z direction. You want to balance
the magnetic force with an electric field so that the particle will continue along a straight
line. The electric field should be in the a. | positive x direction. | b. | positive
z direction. | c. | negative y direction. | d. | negative
x direction. | e. | negative z direction. | | |
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7.
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When a
cathode-ray tube with its axis horizontal is placed in a magnetic field that is directed vertically
upward, the electrons emitted from the cathode follow one of the dashed paths to the face of the
tube. The correct path is
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8.
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A
circular 20-turn coil with a radius of 10 cm carries a current of 3 A. It lies in the xy
plane in a uniform magnetic field B = 0.4 T T + 0.3 T B. The
potential energy of the system is a. | –0.263 J | b. | –0.461
J | c. | –0.564
J | d. | 0.564
J | e. | 0.461
J | | |
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9.
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A
rectangular loop of wire (0.10 m by 0.20 m) carries a current of 5.0 A in a counterclockwise
direction. The loop is oriented as shown in a uniform magnetic field. The magnetic dipole
moment associated with this loop has a value of a. | 0.026 A · m2 | b. | 0.030 A ·
m2 | c. | 0.10 A · m2 | d. | 0.50 A ·
m2 | e. | 1.5 A · m2 | | |
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10.
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A
proton traveling due east 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 | | |
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11.
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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. | down | d. | up | e. | south | | |
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12.
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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 | | |
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13.
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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. | 0.9929 | c. | 0.9874 | d. | 0.9812 | e. | 0.9749 | | |
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14.
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A
0.150-m wire oriented horizontally between the poles of an electromagnet carries a direct current of
12.5 A. The angle between the direction of the current and that of the magnetic field is
25.0°. If the magnetic field strength is 0.625 T, what is the magnitude and direction of
the magnetic force on the wire between the poles?
a. | 1.17 N, upward | b. | 3.30 N,
downward | c. | 0.792 N, upward | d. | 1.44 N,
downward | e. | 0.495 N, upward | | |
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15.
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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.
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16.
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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 | b. | 1.6 ´ 10-6 T | c. | 2.8 ´ 10-6
T | d. | 3.2 ´ 10-6
T | e. | 4.0 ´ 10-6
T | | |
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17.
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A
long wire that carries a current I is bent into five loops as shown in the figure.
If the
observer could "see" the magnetic field inside this arrangement of loops, how would it
appear?
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A
long, straight wire is carrying a current of 5 A in the direction shown in the figure. The
point P is 0.04 m from the wire.
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18.
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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 | | |
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19.
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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 | | |
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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 2.0-A current
as shown. The length of each side of the square is 1.0 m.
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20.
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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 | | |
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Bonus: 5 points (Show your work)
Enter your
answer on the computer, but ignore the evaluation. This will be done by hand!
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21.
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A
proton moving in the plane of the page has a kinetic energy of 6.0 Mev. It enters a magnetic
field of magnitude B=1.0 T directed into the page at an angle of 45° to the linear boundary of
the page as shown. Find x, the distance from the point of entry to where the proton will leave
the field.
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