Magnetic Fields

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Q1) The geographic north pole of the earth is
magnetically a
1) north pole
2) south pole
Q2) The magnetic field of the Earth is useful to us. Why?
1) Enables birds to navigate long distances
2) Deflects dangerous particles from the Sun to the poles
3) Tells us about the interior of the Earth
4) All of the above
5) None of the above
Q3) Cosmic rays (atomic nuclei stripped bare of their electrons)
would continuously bombard Earth’s surface if most of them were
not deflected by Earth’s magnetic field. Given that Earth is, to an
excellent approximation, a magnetic dipole, the intensity of cosmic
rays bombarding its surface is greatest at the
1) poles.
2) mid-latitudes.
3) equator.
Q4) Compared to the huge force that attracts an iron
tack to a strong magnet, the force that the tack exerts on
the magnet is
1) relatively weak
2) equally huge
3) more information is needed
Q5) At any point the magnetic field lines are in the direction of:
1) the magnetic force on a moving positive charge
2) the magnetic force on a moving negative charge
3) the velocity of a moving positive charge
4) the velocity of a moving negative charge
5) none of the above
Q6) (a) Can an electron at rest in a magnetic field be set into
motion by the magnetic field? (b) Can an electron at rest in
an electric field be set into motion by the electric field?
1) (a) yes
2) (a) yes
3) (a) no
4) (a) no
(b) yes
(b) no
(b) no
(b) yes
Q7) An electron moves through a region with a constant magnetic
field B. The work done on the electron by the magnetic field
1) is positive.
2) is equal to zero.
3) is negative.
4) can't be calculated without more information.
Q8) A charged particle, passing through a certain region of space, has a
velocity whose magnitude and direction remain constant. (a) If it is known
that the external magnetic field is zero everywhere in this region, can you
conclude that the external electric field is also zero? (b) If it is know that
the external electric field is zero everywhere, can you conclude that the
external magnetic field is also zero?
1) (a) yes
2) (a) yes
3) (a) no
4) (a) no
(b) yes
(b) no
(b) no
(b) yes
Q9) What is the direction of the magnetic force on the
moving charged particle in each of the three cases below?
1) (a) down
2) (a) down
3) (a) down
4) (a) up
5) (a) up
(b) left
(b) left
(b) right
(b) left
(b) left
(c) out
(c) in
(c) out
(c) out
(c) in
B
B
Case A
+
B
Case B
Case C
Q10) The figure below shows three situations in which a positive particle
of velocity v moves through a uniform magnetic field B and experiences
a magnetic force FB . In each situation, determine whether the orientations
of the vectors are physically reasonable.
1) (a) no (b) no (c) yes
2) (a) no (b) yes (c) no
3) (a) no (b) yes (c) yes
4) (a) yes (b) no (c) yes
5) (a) yes (b) no (c) no
Q11) The figure shows a uniform magnetic field B directed to the
left and a wire carrying a current into the page. The magnetic force
acting on the wire is:
1) toward the top of the page
2) toward the bottom of the page
3) toward the left
4) toward the right
5) zero
Q12) A beam of electrons is sent horizontally down the axis of a
tube to strike a fluorescent screen at the end of the tube. On the
way, the electrons encounter a magnetic field directed vertically
downward. The spot on the screen will therefore be deflected:
1) upward
2) downward
3) to the right as seen from the electron source
4) to the left as seen from the electron source
5) not at all
Q13) Two electrons are located in a region of space where the magnetic
field is zero. Electron A is at rest; and electron B is moving westward with
a constant velocity. A non-zero magnetic field directed eastward is then
applied to the region. In what direction, if any, will each electron be
moving after the field is applied?
1)
2)
3)
4)
5)
electron A
at rest
northward
at rest
southward
upward, away from earth
electron B
westward
eastward
eastward
downward, toward the earth
westward
Q14) A positively charged particle moves to the right in a
magnetic field that points upward. Which way does the magnetic
force on the particle point?
1) Upward
2) Downward
3) Into the board
4) Out of the board
5) There is no force since the velocity and B field are perpendicular
Q15) A negatively charged particle moves to the left in a magnetic
field that points downward. Which way does the magnetic force on
the particle point?
1) Upward
2) Into the board
3) Downward
4) Out of the board
5) There is no force since the velocity and B field are perpendicular
Q16) In a region of space there is a uniform magnetic field pointing
in the positive z direction. In what direction should a negative
charge move to experience a force in the positive x direction?
1) In the positive x direction
2) In the negative x direction
3) In the positive y direction
4) In the negative y direction
5) None of the above
Q17) A uniform magnetic field is in the positive z direction. A
positively charged particle is moving in the positive x direction
through the field. The net force on the particle can be made zero
by applying an electric field in what direction?
1) Positive y
2) Negative y
3) Positive x
4) Negative x
5) Positive z
Q18) An electron travels through a region of space with no
acceleration. Which one of the following statements is the best
conclusion?
1) Both E and B must be zero in that region.
2) E must be zero, but B might be non-zero in that region.
3) E and B might both be non-zero, but they must be mutually
perpendicular.
4) B must be zero, but E might be non-zero in that region.
5) E and B might both be non-zero, but they must point in opposite
directions.
Q19) A positive particle is released from rest in a region of space where
there is constant,
uniform, electric field E , and a constant, uniform

magnetic field B . The electric field points up and the magnetic field
points out of the page in the diagram below. Which path will the positive
particle follow? (All paths shown are in plane of the page.)
A
E
B
C
B(out)
D: it will remain stationary
Q20) If a particle move in a region of space that contains crossed
electric and magnetic fields in opposition, the particle will move in
a straight line (that is, neither force dominates the motion) if its
speed is given by v = E/B. Which of the two forces dominates if
the speed of the particle is v < E/B?
1) the electric force
2) the magnetic force
3) neither force
Q21) A proton traveling due north enters a region that contains
both a magnetic field and an electric field. The electric field lines
point due west. It is observed that the proton continues to travel in
a straight line due north. In which direction must the magnetic field
lines point?
1) up
2) down
3) east
4) west
5) south
Q22) A charged particle moves into a region containing both an electric
and magnetic field. Which of the statements below are true?
A: The particle cannot accelerate in the direction of B.
B: The path of the particle must be a circle.
C: Any change in the particle’s kinetic energy is caused by the E field.
1) Only A
4) Both A&C
2) Only B
5) All are true.
3) Only C
Q23) Three particles move through a region of uniform magnetic
field pointed out of the plane and follow the trajectories shown.
The charges on these particles are
1) q1 < 0, q2 > 0, q3 = 0.
2) q1 > 0, q2 = 0, q3 < 0.
3) q1 < 0, q2 = 0, q3 > 0.
4) q1 = 0, q2 > 0, q3 < 0.
Q24) The figure below shows the path of an electron that passes through
two regions containing uniform magnetic fields of magnitudes B1 and B2.
Its path in each region is a half-circle. (a) What is the direction of B1?
(b) Is the time spent in region 1 greater than, less than, or the same as the
time spent in region 2?
1) (a) into board
2) (a) into board
3) (a) into board
4) (a) out of board
5) (a) out of board
(b) greater than
(b) less than
(b) the same as
(b) less than
(b) the same as
Q25) An electron moves through a region of uniform magnetic
field of magnitude 60 T, directed along the positive direction of
an x axis. The electron has a velocity of (32iˆ  40 ˆj ) km/s as it enters
the field. To an observer looking into the magnetic field region
from the entrance point of the electron, does the electron spiral
clockwise or counterclockwise as it moves deeper into the region?
1) clockwise
2) counterclockwise
Q26) The figure here shows the circular paths of two particles that travel
at the same speed in a uniform magnetic field, which is directed into the
page. One particle is a proton; the other is an electron (which is less
massive). (a) Which particle follows the smaller circle, and (b) does that
particle travel clockwise or counterclockwise?
1) (a) proton
2) (a) proton
3) (a) electron
4) (a) electron
(b) CW
(b) CCW
(b) CW
(b) CCW
Q27) In the following situations a charge q moves in a uniform
magnetic field. The strength of the magnetic field is indicated by
the density of field lines. In all cases the speed of the charge is the
same. For which situation(s) will the charge q travel the greatest
distance in a given time T?
1) 2
2) 4
3) 5
4) 1 & 3
5) none of the above
Q28) The diagram shows a straight wire carrying a flow of
electrons into the page. The wire is between the poles of a
permanent magnet. The direction of the magnetic force exerted on
the wire is:
1) right
2) left
3) up
4) down
5) into the page
Q29) The figure below shows four views of a horseshoe magnet
and a straight wire in which electrons are flowing out of the page,
perpendicular to the plane of the magnet. In which case will the
magnetic force on the wire be directed upwards?
1) a
2) b
3) c
4) d
Q30) A square loop of wire carrying current I is in a uniform
magnetic field B. The loop is perpendicular to B (B out of the
page). What is the direction of the net force on the wire?
1) out of the page
2) into the page
3) 
4) 
5) None of these/don't know
B
I
Q31) A rectangular loop is placed in a uniform magnetic field with
the plane of the loop perpendicular to the direction of the field. If a
current is made to flow through the loop in the sense shown by the
arrows, the field exerts on the loop:
1) a net force.
2) a net torque.
3) a net force and a net torque.
4) neither a net force nor a net torque.
Q32) A rectangular loop is placed in a uniform magnetic field with
the plane of the loop parallel to the direction of the field. If a
current is made to flow through the loop in the sense shown by the
arrows, the field exerts on the loop:
1) a net force.
2) a net torque.
3) a net force and a net torque.
4) neither a net force nor a net torque.
Q33) A current loop is placed in a magnetic field as shown below.
The loop tends to
1) rotate, left side up
2) rotate, right side up
3) rotate, bottom side up
4) rotate, top side up
5) none of the above - it stays in place
Q34) The figure below shows four orientations, at angle , of a magnetic
dipole moment  in a magnetic field. Rank the orientations according to
(a) the magnitude of the torque on the dipole and (b) the potential energy
of the dipole, greatest first.
1) (a) all tie
(b) all tie
2) (a) all tie
(b) 1 & 4, 2 & 3
3) (a) all tie
(b) 2 & 3, 1 & 4
4) (a) 1 & 4, 2 & 3 (b) all tie
5) (a) 1 & 4, 2 & 3 (b) 2 & 3, 1 & 4
Q35) If you place a chunk of iron near the south pole of a
magnet, attraction will occur. Will attraction also occur if
you place the iron near the north pole of a magnet?
1) yes
2) no
Q36) Several paper clips dangle from the north pole of a magnet.
The induced pole in the bottom of the lowermost paper clip is a
1) north pole
2) south pole
3) north or south pole – no difference really
Q37) What would happen if you heated a bar magnet
1) Higher temp means faster motion: magnetic strength would
increase
2) Higher temp means slower motion: magnetic strength would
decrease
3) Higher temp means random motions would knock atoms out of
alignment: magnetic strength would average to zero
4) Magnetism is not related to temperature; no change
Q38) Which one of the following statements concerning permanent
magnets is false?
1) The north pole of a permanent magnet is attracted to a south pole.
2) All permanent magnets are surrounded by a magnetic field.
3) The direction of a magnetic field is indicated by the north pole of a
compass.
4) Magnetic field lines outside a permanent magnet originate from the
north pole and end on the south pole.
5) When a permanent magnet is cut in half, one piece will be a north pole
and one piece will be a south pole.
Q39) A permanent bar magnet is broken
in half. The two pieces are interchanged,
keeping their orientations fixed, as shown
below. Do the pieces attract or repel?
1) Attract
2) Repel
2
1
2
1
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