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wolfson eup3 ch26 test bank

Essential University Physics, 3e (Wolfson)
Chapter 26 Magnetism: Force and Field
26.1 Conceptual Questions
1) A vertical wire carries a current straight down. To the east of this wire, the magnetic field
points
A) toward the north.
B) toward the east.
C) toward the west.
D) toward the south.
E) downward.
Answer: D
Var: 1

2) A current carrying loop of wire lies flat on a table top. When viewed from above, the current
moves around the loop in a counterclockwise sense.
(a) For points OUTSIDE the loop, the magnetic field caused by this current
A) circles the loop in a clockwise direction.
B) circles the loop in a counterclockwise direction.
C) points straight up.
D) points straight down.
E) is zero.

(b) For points INSIDE the loop, the magnetic field caused by this current\
A) circles the loop in a clockwise direction.
B) circles the loop in a counterclockwise direction.
C) points straight up.
D) points straight down.
E) is zero.
Answer: (a) D (b) C
Var: 1

3) A horizontal wire carries a current straight toward you. From your point of view, the magnetic
field at a point directly below the wire points
A) directly away from you.
B) to the left.
C) to the right.
D) directly toward you.
E) vertically upward.
Answer: C
Var: 1

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4) An electron moving in the direction of the +x-axis enters a magnetic field. If the electron
experiences a magnetic deflection in the -y direction, the direction of the magnetic field in this
region points in the direction of the
A) +z-axis.
B) -z-axis.
C) -x-axis.
D) +y-axis.
E) -y-axis.
Answer: B
Var: 1

5) An electron, moving toward the west, enters a uniform magnetic field. Because of this field
the electron curves upward. The direction of the magnetic field is
A) towards the north.
B) towards the south.
C) towards the west.
D) upward.


E) downward.
Answer: A
Var: 1

6) Three particles travel through a region of space where the magnetic field is out of the page, as
shown in the figure. The electric charge of each of the three particles is, respectively,

A) 1 is neutral, 2 is negative, and 3 is positive.
B) 1 is neutral, 2 is positive, and 3 is negative.
C) 1 is positive, 2 is neutral, and 3 is negative.
D) 1 is positive, 2 is negative, and 3 is neutral.
E) 1 is negative, 2 is neutral, and 3 is positive.
Answer: E
Var: 1

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7) A charge is accelerated from rest through a potential difference V and then enters a uniform
magnetic field oriented perpendicular to its path. The field deflects the particle into a circular arc
of radius R. If the accelerating potential is tripled to 3V, what will be the radius of the circular
arc?
A) 9R
B) 3R
C) R
D) R/
E) R/9
Answer: C
Var: 1

8) Ions having equal charges but masses of M and 2M are accelerated through the same potential
difference and then enter a uniform magnetic field perpendicular to their path. If the heavier ions
follow a circular arc of radius R, what is the radius of the arc followed by the lighter?
A) 4R
B) 3R
C) R
D) R/
E) R/2
Answer: D
Var: 1

9) A charged particle is moving with speed v perpendicular to a uniform magnetic field. A second
identical charged particle is moving with speed 2v perpendicular to the same magnetic field. If
the frequency of revolution of the first particle is f, the frequency of revolution of the second
particle is
A) f.
B) 2f.
C) 4f.
D) f/2.
E) f/4.
Answer: A
Var: 1

10) A vertical wire carries a current vertically upward in a region where the magnetic field vector
points toward the north. What is the direction of the magnetic force on this current due to the
field?
A) downward
B) toward the north
C) toward the south
D) toward the east
E) toward the west
Answer: E
Var: 1

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11) 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 upward.
B) points downward.
C) points toward you.
D) points away from you.
E) is zero.
Answer: B
Var: 1

12) The figure shows two long wires carrying equal currents I1 and I2 flowing in opposite
directions. Which of the arrows labeled A through 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 zero at that point.
Answer: B
Var: 1

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13) The figure shows four different sets of insulated wires that cross each other at right angles
without actually making electrical contact. The magnitude of the current is the same in all the
wires, and the directions of current flow are as indicated. For which (if any) 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 not equal to zero in any of these cases.
Answer: C
Var: 1

14) A negatively charged particle is moving to the right, directly above a wire having a current
flowing to the right, as shown in the figure. In which direction is the magnetic force exerted on
the particle?

A) into the page
B) out of the page
C) downward
D) upward
E) The magnetic force is zero since the velocity is parallel to the current.
Answer: D
Var: 1

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15) Two very long parallel wires are a distance d apart and carry equal currents in opposite
directions. The locations where the net magnetic field due to these currents is equal to zero are
A) midway between the wires.
B) a distance d/2 to the left of the left wire and also a distance d/2 to the right of the right wire.
C) a distance d to the left of the left wire and also a distance d to the right of the right wire.
D) a distance d/ to the left of the left wire and also a distance d/ to the right of the right
wire.
E) The net field is not zero anywhere.
Answer: E
Var: 1

16) Two very long parallel wires in the xy-plane, a distance 2a apart, are parallel to the y-axis and
carry equal currents I as shown in the figure. The +z direction points perpendicular to the xyplane in a right-handed coordinate system. If both currents flow in the +y direction, which one of
the graphs shown in the figure below best represents the z component of the net magnetic field,
in the xy-plane, as a function of x? (Caution: These graphs are not magnetic field lines.)

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A) 1
B) 2
C) 3
D) 4
E) 5
Answer: C
Var: 1

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17) Two very long parallel wires in the xy-plane, a distance 2a apart, are parallel to the y-axis and
carry equal currents I as shown in the figure. The +z direction points perpendicular to the xyplane in a right-handed coordinate system. If the left current flows in the +y direction and the
right current flows in the -y direction, which one of the graphs shown in the figure below best
represents the z component of the net magnetic field, in the xy-plane, as a function of x?
(Caution: These graphs are not magnetic field lines.)

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A) 1
B) 2
C) 3
D) 4
E) 5
Answer: D
Var: 1

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18) The figure 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 on current 1 is equal to zero.
Answer: A
Var: 1

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19) The figure shows three long, parallel, current-carrying wires. The current directions are
indicated for currents I1 and I3. The arrow labeled F represents the net magnetic force acting on
current I3. The three 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) vertically upward
D) vertically downward
E) out of the picture (in the same direction as I1 and I3)
Answer: A
Var: 1

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20) A long straight conductor has a constant current flowing to the right. A wire rectangle is
situated above the wire, and also has a constant current flowing through it (as shown in the
figure). Which of the following statements is true?

A) The net magnetic force on the wire rectangle is upward, and there is also a net torque on the
it.
B) The net magnetic force on the wire rectangle is zero, and the net torque on it is zero.
C) The net magnetic force on the wire rectangle is downward, and there is also a net torque on
the it.
D) The net magnetic force on the wire rectangle is zero, but there is a net torque on it.
E) The net magnetic force on the wire rectangle is downward, and the net torque on it is zero.
Answer: E
Var: 1

21) A ring with a clockwise current (as seen from above the ring) is situated with its center
directly above another ring, which has a counter-clockwise current, as shown in the figure. In
what direction is the net magnetic force exerted on the top ring?

A) upward
B) downward
C) to the right
D) to the left
E) The net force is zero.
Answer: A
Var: 1

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22) A very long, hollow, thin-walled conducting cylindrical shell (like a pipe) of radius R carries
a current along its length uniformly distributed throughout the thin shell. Which one of the
graphs shown in the figure most accurately describes the magnitude B of the magnetic field
produced by this current as a function of the distance r from the central axis?

A) 1
B) 2
C) 3
D) 4
E) 5
Answer: D
Var: 1

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23) A very long, solid, conducting cylinder of radius R carries a current along its length
uniformly distributed throughout the cylinder. Which one of the graphs shown in the figure most
accurately describes the magnitude B of the magnetic field produced by this current as a function
of the distance r from the central axis?

A) 1
B) 2
C) 3
D) 4
E) 5
Answer: A
Var: 1

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24) Consider a solenoid of length L, N windings, and radius b (L is much longer than b). A
current I is flowing through the wire. If the radius of the solenoid were doubled (becoming 2b),
and all other quantities remained the same, the magnetic field inside the solenoid would
A) remain the same.
B) become twice as strong.
C) become one half as strong.
Answer: A
Var: 1

25) Consider a solenoid of length L, N windings, and radius b (L is much longer than b). A
current I is flowing through the wire. If the length of the solenoid became twice as long (2L), and
all other quantities remained the same, the magnetic field inside the solenoid would
A) remain the same.
B) become twice as strong.
C) become one half as strong.
Answer: C
Var: 1

26.2 Problems
1) An electron moves with a speed of 8.0 × 106 m/s along the +x-axis. It enters a region where
there is a magnetic field of 2.5 T, directed at an angle of 60° to the +x-axis and lying in the xyplane. (1 eV = 1.60 × 10-19 C, mel = 9.11 × 10-31 kg) Calculate the magnitude of
(a) the magnetic force on the electron.
(b) the acceleration of the electron.
Answer: (a) 2.8 × 10-12 N (b) 3.0 × 1018 m/s2
Var: 1

2) An electron traveling toward the north with speed 4.0 × 105 m/s enters a region where the
Earth's magnetic field has the magnitude 5.0 × 10-5 T and is directed downward at 45° below
horizontal. What is the magnitude of the force that the Earth's magnetic field exerts on the
electron? (e = 1.60 × 10-19 C)
A) 2.3 × 10-18 N
B) 3.2 × 10-18 N
C) 2.3 × 10-19 N
D) 3.2 × 10-19 N
E) 2.3 × 10-20 N
Answer: A
Var: 1

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3) A uniform magnetic field of magnitude 0.80 T in the negative z direction is present in a region
of space, as shown in the figure. A uniform electric field is also present and is set at 76,000 V/m
in the +y direction. An electron is projected with an initial velocity v0 = 9.5 × 104 m/s in the +x
direction. The y component of the initial force on the electron is closest to which of the following
quantities? (e = 1.60 × 10-19 C)

A) -2.4 × 10-14 N
B) +2.4 × 10-14 N
C) -1.0 × 10-14 N
D) +1.0 × 10-14 N
E) zero
Answer: A
Var: 1

4) A particle with charge -5.00 C initially moves at
magnetic field

= (1.00 + 7.00 ) m/s. If it encounters a

find the magnetic force vector on the particle.

A) (-350 + 50.0 ) N
B) (-350 - 50.0 ) N
C) (350 + 50.0 ) N
D) (350 - 50.0 ) N
Answer: A
Var: 50+

5) A proton, with mass 1.67 × 10-27 kg and charge +1.6 × 10-19 C, is sent with velocity 7.1 ×
104 m/s in the +x direction into a region where there is a uniform electric field of magnitude 730
V/m in the +y direction. What are the magnitude and direction of the uniform magnetic field in
the region, if the proton is to pass through undeflected? Assume that the magnetic field has no xcomponent and neglect gravitational effects.
Answer: 0.010 T, +z direction
Var: 1

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6) A uniform magnetic field of magnitude 0.80 T in the negative z-direction is present in a region
of space, as shown in the figure. A uniform electric field is also present. An electron that is
projected with an initial velocity

in the positive x-direction passes through the

region without deflection. What is the electric field vector in the region?

A) -73 kV/m
B) +73 kV/m
C) +110 kV/m
D) +110 kV/m
E) -110 kV/m
Answer: A
Var: 50+

7) A beam of electrons is accelerated through a potential difference of 10 kV before entering a
region having uniform electric and magnetic fields that are perpendicular to each other and
perpendicular to the direction in which the electron is moving. If the magnetic field in this
region has a value of 0.010 T, what magnitude of the electric field is required if the particles are
to be undeflected as they pass through the region?
A) 2.3 × 103 V/m
B) 7.9 × 103 V/m
C) 5.9 × 105 V/m
D) 6.0 × 105 V/m
E) 7.2 × 106 V/m
Answer: C
Var: 1

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8) An electron moving with a velocity = 5.0 × 107 m/s enters a region of space where
perpendicular electric and a magnetic fields are present. The electric field is = . What
magnetic field will allow the electron to go through the region without being deflected?
A) = +2.0 × 10-4 T
B)

= -2.0 × 10-4 T

C)

= +2.0 × 10-4 T

D)

= -2.0 × 10-4 T

E) = +5.0 × 10-4 T
Answer: C
Var: 1

9) The figure shows a velocity selector that can be used to measure the speed of a charged
particle. A beam of particles is directed along the axis of the instrument. A parallel plate capacitor
sets up an electric field E, which is oriented perpendicular to a uniform magnetic field B. If the
plates are separated by 2.0 mm and the value of the magnetic field is 0.60 T, what voltage
between the plates will allow particles of speed 5.0 × 105 m/s to pass straight through without
deflection?

A) 600 V
B) 1900 V
C) 3800 V
D) 190 V
E) 94 V
Answer: A
Var: 50+

10) An alpha particle is moving at a speed of 5.0 × 105 m/s in a direction perpendicular to a
uniform magnetic field of strength 0.040 T. The charge on an alpha particle is 3.2 × 10-19 C and
its mass is 6.6 × 10-27 kg.
(a) What is the radius of the path of the alpha particle?
(b) How long does it take the alpha particle to make one complete revolution around its path?
Answer: (a) 0.26 m (b) 3.2 µs
Var: 1
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11) An electron moving perpendicular to a uniform magnetic field of 3.2 × 10-2 T moves in a
circle of radius 0.40 cm. How fast is this electron moving? (mel = 9.11 × 10-31 kg. e = 1.60 ×
10-19 C)
A) 2.2 × 107 m/s
B) 1.9 × 10-2 m/s
C) 1.9 × 10-30 m/s
D) 3.0 × 106 m/s
E) 8.0 × 106 m/s
Answer: A
Var: 1

12) As shown in the figure, a small particle of charge q = -7.0 ×
has velocity

C and mass

as it enters a region of uniform magnetic

field. The particle is observed to travel in the semicircular path shown, with radius R = 5.0 cm.
Calculate the magnitude and direction of the magnetic field in the region.

Answer: 0.083 T, directed into the paper
Var: 50+

13) A proton starting from rest travels through a potential of 1.0 kV and then moves into a
uniform 0.040-T magnetic field. What is the radius of the proton's resulting orbit? (mproton =
1.67 × 10-27 kg, e = 1.60 × 10-19 C)
A) 0.080 m
B) 0.11 m
C) 0.14 m
D) 0.17 m
E) 0.19 m
Answer: B
Var: 1

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14) A proton is first accelerated from rest through a potential difference V and then enters a
uniform 0.750-T magnetic field oriented perpendicular to its path. In this field, the proton
follows a circular arc having a radius of curvature of 1.84 cm. What was the potential difference
V? (mproton = 1.67 × 10-27 kg, e = 1.60 × 10-19 C)
Answer: 9.12 kV
Var: 1

15) A charged particle of mass 0.0020 kg is subjected to a
magnetic field which acts at a
right angle to its motion. If the particle moves in a circle of radius
at a speed of
what is the magnitude of the charge on the particle?
A) 0.0083 C
B) 120 C
C) 0.00040 C
D) 2500 C
Answer: A
Var: 50+

16) In a mass spectrometer, a singly-charged particle (charge e) has a speed of 1.0 × 106 m/s and
enters a uniform magnetic field of 0.20 T. The radius of the circular orbit of the particle is 0.020
m. What is the mass of this particle? (e = 1.60 × 10-19 C)
A) 3.2 × 10-28 kg
B) 6.4 × 10-28 kg
C) 1.7 × 10-27 kg
D) 4.5 × 10-27 kg
E) 3.1 × 10-31 kg
Answer: B
Var: 1

17) A doubly charged ion (charge 2e) with velocity 6.9 × 106 m/s moves in a circular path of
diameter 60.0 cm in a magnetic field of 0.80 T in a mass spectrometer. What is the mass of this
ion? (e = 1.60 × 10-19 C)
A) 11 × 10-27 kg
B) 6.7 × 10-27 kg
C) 4.5 × 10-27 kg
D) 3.3 × 10-27 kg
E) 8.2 × 10-27 kg
Answer: A
Var: 1

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18) An electron enters a magnetic field of
with a velocity perpendicular to the direction of
the field. At what frequency does the electron traverse a circular path? (mel = 9.11 × 10-31 kg, e
= 1.60 × 10-19 C)
A) 2.1 × 1010 Hz
B) 4.8 × 10-7 Hz
C) 2.1 × 1014 Hz
D) 4.8 × 10-11 Hz
Answer: A
Var: 50+

19) Alpha particles (charge = +2e, mass = 6.68 ×
kg, e = 1.60 × 10-19 C) are accelerated
in a cyclotron to a final orbit radius of
The magnetic field in the cyclotron is
The
period of the circular motion of the alpha particles is closest to
A) 0.44 μs.
B) 0.67 μs.
C) 0.87 μs.
D) 1.1 μs.
E) 1.3 μs.
Answer: A
Var: 50+

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20) A wire in the shape of an "M" lies in the plane of the paper. It carries a current of 2.0 A,
flowing from points A to E, as shown in the figure. It is placed in a uniform magnetic field of
0.75 T in the same plane, directed as shown on the right side of the figure. The figure indicates
the dimensions of the wire. What are the magnitude and direction of the force acting on

(a) section AB of this wire?
(b) section BC of this wire?
(c) section CD of this wire?
(d) section DE of this wire?
(e) the entire wire?
Answer: (a) 0.11 N perpendicular out of the page
(b) 0.00 N
(c) 0.090 N perpendicular out of the page
(d) 0.11 N perpendicular into the page
(e) 0.090 N perpendicular out of the page
Var: 1

21) A straight wire that is 0.60 m long is carrying a current of 2.0 A. It is placed in a uniform
magnetic field of strength 0.30 T. If the wire experiences a force of 0.18 N, what angle does the
wire make with respect to the magnetic field?
A) 25°
B) 30°
C) 35°
D) 60°
E) 90°
Answer: B
Var: 1

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22) A thin copper rod that is 1.0 m long and has a mass of 0.050 kg is in a magnetic field of 0.10
T. What minimum current in the rod is needed in order for the magnetic force to cancel the
weight of the rod?
A) 1.2 A
B) 2.5 A
C) 4.9 A
D) 7.6 A
E) 9.8 A
Answer: C
Var: 1

23) A wire carries a 4.0-A current along the +x-axis through a magnetic field
T. If the wire experiences a force of 30 N
A) 1.1 m
B) 0.87 m
C) 1.5 m
D) 0.63 m
Answer: A

= (5.0 + 7.0 )

as a result, how long is the wire?

Var: 1

24) A straight 15.0-g wire that is 2.00 m long carries a current of 8.00 A. This wire is aligned
horizontally along the west-east direction with the current going from west to east. You want to
support the wire against gravity using the weakest possible uniform external magnetic field.
(a) Which way should the magnetic field point?
(b) What is the magnitude of the weakest possible magnetic field you could use?
Answer: (a) from south to north (b) 9.19 × 10-3 T
Var: 1

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25) An L-shaped metal machine part is made of two equal-length segments that are perpendicular
to each other and carry a 4.50-A current as shown in the figure. This part has a total mass of 3.80
kg and a total length of 3.00 m, and it is in an external 1.20-T magnetic field that is oriented
perpendicular to the plane of the part, as shown. What is the magnitude of the NET magnetic
force that the field exerts on the part?

A) 8.10 N
B) 11.5 N
C) 16.2 N
D) 22.9 N
E) 32.4 N
Answer: B
Var: 1

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26) A wire segment 1.2 m long carries a current I = 3.5 A and is oriented as shown in the figure.
A uniform magnetic field of magnitude 0.50 T pointing toward the -x direction is present as
shown. The +z-axis points directly into the page. What is the magnetic force vector on the wire
segment?

A) +1.6 N
B) -1.6 N
C) +1.6 N
D) (+1.3 - 1.6 ) N
E) (-1.3 + 1.6
Answer: C

N

Var: 1

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