Two long parallel wires 20 cm apart carry currents of 5A and 8A in the same direction. Is there any point between the two wires where the magnetic field is zero?

1
Two long parallel wires 20 cm apart carry
currents of 5A and 8A in the same direction. Is
there any point between the two wires where the
magnetic field is zero?

1. Yes, midway between the wires.
2. Yes, 12 cm from the 5A wire.
3. Yes, 7.7 cm from the 5A wire.
4. No.

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2
A rectangular coil (0.20 m x 0.80 m) has 200
turns and is in a uniform magnetic field of 0.30
T. If the orientation of the coil is varied
through all possible positions, the maximum
torque on the coil by magnetic forces is 0.080
N-m. What is the current in the coil?

1. 5.0 mA
2. 1.7 A
3. 8.3 mA
4. 1.0 A

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3
A circular coil (radius 0.40 m) has 160 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 0.16 N-m when the
current in the coil is 4.0 mA. What is the
magnitude of the magnetic field?

1. 0.37 T
2. 1.6 T
3. 0.50 T
4. 1.2 T

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4
A high-voltage powerline 20 m above the ground
carries a current of 2000 A. What is the magnetic
field due to the current directly underneath the
powerline? (µ 0 4? x 10-7 T-m/A)

1. 20.0 µ T
2. 35.0 µ T
3. 14.0 mT
4. 0.3 T

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5
A superconducting solenoid is to be designed to
generate a magnetic field of 10 T. If the
solenoid winding has 2000 turns/meter, what is
the required current? (µ 0 4? x 10-7 A-m/T)

1. 1000 A
2. 1990 A
3. 3980 A
4. 5000 A

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6
An incredible amount of electrical energy passes
down the funnel of a large tornado every second.
Measurements taken in Oklahoma at a distance of 9
km from a large tornado showed an almost constant
magnetic field of 1.5 x 10-8 T associated with
the tornado. What was the average current -going
down the funnel? (µ 0 4? x 10-7 A-m/T)

1. 150 A
2. 250 A
3. 350 A
4. 500 A

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7
Superconductors are capable of carrying very
large currents with no resistance. If a
superconducting wire is formed into a solenoid of
length 50 cm with 500 turns, what is the magnetic
field inside the solenoid when the current is 104
A? ( µ 0 4? x 10-7 A-m/T)

1. 1.25 T
2. 2.50 T
3. 6.28 T
4. 12.6 T

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8
In a mass spectrometer, an ion will have a
smaller radius for its circular path if

1. its speed is greater
2. its mass is greater
3. its charge is greater
4. the magnetic field is weaker

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9
A current in a long, straight wire produces a
magnetic field, and these magnetic field lines

1. go out from the wire to infinity
2. come in from infinity to the wire
3. form circles which pass through the wire
4. form circles which go around the circle

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10
Consider two long, straight parallel wires, each
carrying a current I. If the currents are flowing
in opposite directions

1. the two wires will attract each other
2. the two wires will repel each other
3. the two wires will exert a torque on each other
4. neither wire will exert a force on the other

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11
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

1. energy
2. momentum
3. radius for the circle
4. time to go around the circle once

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12
A superconducting wire carries a current of 104
A. Find the magnetic field at a distance of 1.0 m
from the wire. ( µ 0 4? x 10-7 A-m/T)

1. 2.0 x 10-3 T
2. 8.0 x 10-3 T
3. 1.6 x 10-2 T
4. 3.2 x 10-2 T

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13
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

1. 2ILB
2. ILB
3. IBL2
4. zero

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14
A galvanometer can be used to make either an
ammeter or a voltmeter. Under which condition
will the deflection of the needle be greatest
when a very small current flows through the
device?

1. the current goes through the original
   galvanometer.
2. the current goes through the voltmeter.
3. the voltmeter and the original galvanometer will
   give the same deflection if the current is the
   same.
4. the current goes through the ammeter.

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15
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

1. 2ILB
2. ILB
3. IBL2
4. zero

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16
An electron which moves with a speed of 3 x 104
m/s perpendicular to a uniform magnetic field of
0.40 T experiences a force of what magnitude? (qe
1.6 x 10-19 C)

1. 4.8 x 10-14 N
2. 19.2 x 10-16 N
3. 2.2 x 10-24 N
4. zero

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17
A 2.0 m wire segment carrying a current of 0.60 A
oriented parallel to a uniform magnetic field of
0.50 T experiences a force of what magnitude?

1. 6.7 N
2. 0.30 N
3. 0.15 N
4. zero

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18
A proton moving with a speed of 3 x 105 m/s
perpendicular to a uniform magnetic field of 0.20
T will follow which of the paths described below?
(qe 1.6 x 10-19 C and mp 1.67 x 10-27 kg)

1. a straight line path
2. a circular path of 1.5 cm radius
3. a circular path of 3.0 cm radius
4. a circular path of 0.75 cm radius

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19
If a deuteron, with the same charge but twice the
mass of a proton, were to move with a speed of 3
x 105 m/s perpendicular to a uniform magnetic
field of 0.20 T, it would follow which of the
paths described below? (qp 1.6 x 10-19 C and
md 3.34 x 10-27 kg)

1. a straight line path
2. a circular path of 1.5 cm radius
3. a circular path of 3.0 cm radius
4. a circular path of 0.75 cm radius

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20
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

1. north
2. south
3. east
4. west

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21
A stationary positive charge Q, located in a
magnetic field B, which is directed toward the
right as indicated. The direction of the magnetic
force on Q is

1. toward the right
2. up
3. down
4. there is no magnetic force

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22
A wire is lying horizontally in the north-south
direction and the horizontal magnetic field is
toward the east. There are some positive charges
in the wire moving north and equal number of
negative charges moving south. The direction of
the force on the wire will be

1. east
2. down, into the page
3. up, out of the page
4. there is no magnetic force

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23
There is a magnetic force on a particle. It is
possible that the particle is

1. uncharged
2. stationary
3. moving in the direction of the magnetic field
4. not part of a wire

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24
Electrical charges and magnetic poles have many
similarities. However, one difference between the
two is that

1. opposite magnetic poles repel
2. one magnetic pole cannot create magnetic poles in
   other materials
3. a magnetic pole cannot be isolated
4. magnetic poles do not produce magnetic fields

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25
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 3.35 cm while isotope Y moves
along a 3.43 cm radius path. What is the ratio of
the two isotope masses, mX /mY ?

1. 0.977
2. 1.023
3. 1.048
4. 0.954

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26
A 10 ohm, 25 mA galvanometer is to be converted
into an ammeter which reads 5 A at a full scale
deflection. What resistance should be placed in
parallel with the galvanometer coil?

1. 2.5 ohms
2. 0.5 ohms
3. 0.25 ohms
4. 0.05 ohms

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27
A proton which moves perpendicular to a magnetic
field of 1.2 T in a circular path of 0.08 m
radius, has what speed? (qp 1.6 x 10-19 C and
mp 1.67 x 10 -27 kg)

1. 3.4 x 106 m/s
2. 4.6 x 106 m/s
3. 9.6 x 106 m/s
4. 9.2 x 106 m/s

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28
A 10 ohm, 25 mA galvanometer is to be converted
into a voltmeter which reads 20 V at full scale
deflection. What resistance should be placed in
series with the galvanometer coil?

1. 810 ohms
2. 790 ohms
3. 500 ohms
4. 450 ohms

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29
A 10 ohm, 15 mA galvanometer is converted into an
ammeter by placing a 1.5 x 10-2 ohm shunt in
parallel with the galvanometer coil. What is the
maximum scale reading on the galvanometer?

1. 25.0 A
2. 15.0 A
3. 10.0 A
4. 5.0 A

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30
A circular loop carrying a current of 2.0 A is
oriented in a magnetic field of 3.5 T. The loop
has an area of 0.12 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?

1. 58 N-m
2. 6.8 N-m
3. 0.84 N-m
4. 0.17 N-m

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31
A circular loop carrying a current of 2.0 A is
oriented in a magnetic field of 3.5 T. The loop
has an area of 0.12 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 37
angle to the field?

1. 46.0 N-m
2. 0.67 N-m
3. 0.51 N-m
4. 0.10 N-m

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32
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 horizontal
component of the earth's magnetic field is due
north at this point and has a strength of 0.14 x
10-4 T. What is the direction of the force on
the wire?

1. out of the earth's surface
2. toward the earth's surface
3. due east
4. 40 S of E

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33
A current carrying wire of length 50 cm is
positioned perpendicular to a uniform magnetic
field. If the current is 10.0 A and it is
determined that there is a resultant force of 3.0
N on the wire due to the interaction of the
current and field, what is the magnetic field
strength?

1. 0.6 T
2. 1.50 T
3. 1.85 x 103 T
4. 6.7 x 103 T

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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 horizontal
component of the earth's magnetic field is due
north at this point and has a strength of 0.14 x
10-4 T. What is the size of the force on the
wire?

1. 0.28 x 10-4 N
2. 2.5 x 10-4 N
3. 1.9 x 10-4 N
4. 1.6 x 10-4 N

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35
An electron moves across the earth's equator at a
speed of 2.5 x 106 m/s and in a direction 35 N
of E. At this point the earth's magnetic field
has a direction due north, is parallel to the
surface, and has a value of 0.10 x 10-4 T. What
is the direction of the force acting on the
electron at this instant?

1. due west
2. into the earth's surface
3. out of the earth's surface
4. due south

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36
A proton is released such that it has an initial
speed of 4 x 105 m/s from left to right across
the page. A magnetic field of 1.2 T is present at
an angle of 30 to the horizontal direction (or
positive x-axis). What is the magnitude of the
force experienced by the proton? (qp 1.6 x
10-19 C)

1. 4.8 x 10-25 N
2. 1.3 x 10-19 N
3. 3.8 x 10-14 N
4. 7.5 x 103 N

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37
An electron moves across the earth's equator at a
speed of 2.5 x 106 m/s and in a direction 35 N
of E. At this point the earth's magnetic field
has a direction due north, is parallel to the
surface, and has a value of 0.10 x 10-4 T. What
is the magnitude of the force acting on the
electron due to its interaction with the earth's
magnetic field? (qe -1.6 x 10-19 C)

1. 5.1 x 10-18 N
2. 4.0 x 10-18 N
3. 3.3 x 10-18 N
4. 2.3 x 10-18 N

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38
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?

1. out of the page
2. into the page
3. from bottom edge to top edge of the page
4. from right to left across the page

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39
Geo-physicists today generally attribute the
existence of the earth's magnetic field to which
of the following?

1. convection currents within the liquid interior
2. iron ore deposits in the crust
3. nickel-iron deposits in the crust
4. solar flares

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40
The term magnetic declination refers to which of
the following?

1. angle between earth's magnetic field and earth's
   surface
2. earth's magnetic field strength at the equator
3. tendency for earth's field to reverse itself
4. angle between directions to true north and
   magnetic north

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41
The magnetic field of the earth is believed
responsible for which of the following?

1. deflection of both charged and uncharged cosmic
   rays
2. deflection of charged cosmic rays
3. ozone in the upper atmosphere
4. solar flares

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42
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?

1. out of the page
2. to the right
3. to the left
4. into the page

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43
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 which
of the following?

1. number turns in loop
2. current strength
3. both of the choices are valid
4. none of the choices are valid

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44
A circular current loop is placed in an external
magnetic field. How is the torque related to the
radius of the loop?

1. directly proportional to radius
2. inversely proportional to radius
3. directly proportional to radius squared
4. inversely proportional to radius squared

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45
The path of a charge particle moving parallel to
a uniform magnetic field will be which of the
following?

1. straight line
2. circle
3. ellipse
4. parabola

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46
The current in a long wire creates a magnetic
field in the region around the wire. How is the
strength of that field at a given distance, r,
from the wire center related to the magnitude of
the field?

1. field directly proportional to r
2. field inversely proportional to r
3. field directly proportional to r2
4. field inversely proportional to r2

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47
The direction of the force on a current carrying
wire located in an external magnetic field is
which of the following?

1. perpendicular to the current
2. perpendicular to the field
3. both of the choices are valid
4. none of the choices are valid

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48
A current in a solenoid coil creates a magnetic
field inside that coil. The field strength is
directly proportional to which of the following?

1. coil area
2. current
3. both current and coil area
4. none of these

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49
Which of the following devices makes use of an
electromagnet?

1. loudspeaker
2. galvanometer
3. both of the choices
4. none of the choices

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50
The magnetic domains in a non-magnetized piece of
iron are characterized by which orientation?

1. parallel to the magnetic axis
2. anti-parallel to the magnetic axis
3. random
4. perpendicular to the magnetic axis

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51
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?

1. zero
2. 180
3. 90
4. 45

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52
A solenoid with 500 turns, 0.10 m long, carrying
a current of 4.0 A and with a radius of 10-2 m
will have what strength magnetic field at its
center? (magnetic permeability in empty space µ
0 4? x 10 -7 T-m/A)

1. 31 x 10-4 T
2. 62 x 10-4 T
3. 125 x 10-4 T
4. 250 x 10-4 T

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53
The force exerted on a current carrying wire
located in an external magnetic field is directly
proportional to which of the following?

1. current strength
2. field strength
3. both of the choices
4. none of the choices are valid

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54
A thin copper rod 1.0 m long has a mass of 50
grams. What is the minimum current in the rod
that would allow it to "float" in a magnetic
field of 0.1T?

1. 1.23 A
2. 2.45 A
3. 4.9 A
4. 9.8 A

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55
A 100 m long wire carrying a current of 4.0 A
will be accompanied by a magnetic field of what
strength at a distance of 0.05 m from the wire?
(magnetic permeability in empty space µ 0 4?
x 10-7 T-m/A)

1. 4.0 x 10-5 T
2. 2.0 x 10-5 T
3. 1.6 x 10-5 T
4. zero

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56
Two parallel conductors each of 0.5 m length,
separated by 5 x 10-3 m and carrying 3.0 A in
opposite directions, will experience what type
and magnitude of mutual force? (magnetic
permeability in empty space µ 0 4? x 10-7
T-m/A)

1. attractive, 0.06 x 10-4 N
2. repulsive, 0.60 x 10-4 N
3. attractive, 1.8 x 10-4 N
4. repulsive, 1.8 x 10-4 N

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57
At the Fermilab accelerator in Weston, Illinois,
protons with momentum 4.8 x 10-16 kg-m/s are
held in a circular orbit of radius 1 km by an
upward magnetic field. What upward B-field must
be used to maintain the protons in this orbit?
(qp 1.6 x 10-19 C)

1. 1 T
2. 2 T
3. 3 T
4. 4 T

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58
An electron moves through a region of crossed
electric and magnetic fields. The electric field
E 1000 V/m and is directed straight down. The
magnetic field B 0.4 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?

1. 2500 m/s
2. 4000 m/s
3. 5000 m/s
4. 8000 m/s

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59
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 0.1 T,
determine the maximum current a 4-mm diameter
niobium wire can carry and remain
superconducting. ( µ 0 4? x 10-7 A-m/T)

1. 125 A
2. 250 A
3. 500 A
4. 1000 A

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60
A proton, mass 1.67 x 10-27 kg and charge 1.6 x
10-19 C, moves in a circular orbit perpendicular
to a uniform magnetic field of 0.75 T. Find the
time for the proton to make one complete circular
orbit.

1. 4.3 x 10-8 s
2. 8.7 x 10-8 s
3. 4.9 x 10-7 s
4. 9.8 x 10-7 s

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