Self Test: Week 7



1.
Units of a magnetic field might be:
A.
C⋅m/s
B.
C⋅s/m
C.
C/kg
D.
kg/C⋅s
E.
N/C⋅m


2.
In the formula ¢ = q² × 4:
A.
¢ must be perpendicular to ² but not necessarily to 4
B.
¢ must be perpendicular to 4 but not necessarily to ²
C.
² must be perpendicular to 4 but not necessarily to ¢
D.
all three vectors must be mutually perpendicular
E.
¢ must be perpendicular to both ² and 4


3.
An electron moves in the negative x direction, through a uniform magnetic field in the negative y direction. The magnetic force on the electron is:
A.
in the negative x direction
B.
in the positive y direction
C.
in the negative y direction
D.
in the positive z direction
E.
in the negative z direction


4.
At any point the magnetic field lines are in the direction of:
A.
the magnetic force on a moving positive charge
B.
the magnetic force on a moving negative charge
C.
the velocity of a moving positive charge
D.
the velocity of a moving negative charge
E.
none of the above


5.
The magnetic force on a charged particle is in the direction of its velocity if:
A.
it is moving in the direction of the field
B.
it is moving opposite to the direction of the field
C.
it is moving perpendicular to the field
D.
it is moving in some other direction
E.
never


6.
A magnetic field exerts a force on a charged particle:
A.
always
B.
never
C.
if the particle is moving across the field lines
D.
if the particle is moving along the field lines
E.
if the particle is at rest


7.
The direction of the magnetic field in a certain region of space is determined by firing a test charge into the region with its velocity in various directions in different trials. The field direction is:
A.
one of the directions of the velocity when the magnetic force is zero
B.
the direction of the velocity when the magnetic force is a maximum
C.
the direction of the magnetic force
D.
perpendicular to the velocity when the magnetic force is zero
E.
none of the above


8.
An electron is moving north in a region where the magnetic field is south. The magnetic force exerted on the electron is:
A.
zero
B.
up
C.
down
D.
east
E.
west


9.
A magnetic field CANNOT:
A.
exert a force on a charge
B.
accelerate a charge
C.
change the momentum of a charge
D.
change the kinetic energy of a charge
E.
exist


10.
A proton (charge e), traveling perpendicular to a magnetic field, experiences the same force as an alpha particle (charge 2e) which is also traveling perpendicular to the same field. The ratio of their speeds, vproton/valpha is:
A.
0.5
B.
1
C.
2
D.
4
E.
8


11.
An electron (charge = –1.6 × 10–19 C) is moving at 3 × 105 m/s in the positive x direction. A magnetic field of 0.8 T is in the positive z direction. The magnetic force on the electron is:
A.
0
B.
4 × 10–14 N in the positive z direction
C.
4 × 10–14 N in the negative z direction
D.
4 × 10–14 N in the positive y direction
E.
4 × 10–14 N in the negative y direction


12.
At one instant an electron (charge = –1.6 × 10–19 C) is moving in the xy plane, the components of its velocity being vx = 5 × 105 m/s and vy = 3 × 105 m/s. A magnetic field of 0.8 T is in the positive x direction. At that instant the magnitude of the magnetic force on the electron is:
A.
0
B.
2.6 × 10–14 N
C.
3.8 × 10–14 N
D.
6.4 × 10–14 N
E.
1.0× 10–13 N


13.
An electron travels due north through a vacuum in a region of uniform magnetic field 4 that is also directed due north. It will:
A.
be unaffected by the field
B.
speed up
C.
slow down
D.
follow a right-handed corkscrew path
E.
follow a left-handed corkscrew path


14.
An electron is launched with velocity ² in a uniform magnetic field 4. The angle θ between ² and 4 is between 0 and 90o. As a result, the electron follows a helix, its velocity vector ² returning to its initial value in a time interval of:
A.
2π?m/eB
B.
2π?mv/eB
C.
2π?mv sinθ /eB
D.
2π?mv cosθ /eB
E.
none of these


15.
A charged particle is projected into a region of uniform, parallel, ® and 4 fields. The force on the particle is:
A.
zero
B.
at some angle < 90° with the field lines
C.
along the field lines
D.
perpendicular to the field lines
E.
unknown (need to know the sign of the charge)


16.
The current is from left to right in the conductor shown. The magnetic field is into the page and point S is at a higher potential than point T. The charge carriers are:
A.
positive
B.
negative
C.
neutral
D.
absent
E.
moving near the speed of light


17.
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:
A.
B.
C.
D.
E.
into the page


18.
The figure shows the motion of electrons in a wire which is near the N pole of a magnet. The wire will be pushed:
A.
toward the magnet
B.
away from the magnet
C.
downwards
D.
upwards
E.
along its length


19.
The figure shows a uniform magnetic field 4 directed to the left and a wire carrying a current into the page. The magnetic force acting on the wire is:
A.
toward the top of the page
B.
toward the bottom of the page
C.
toward the left
D.
toward the right
E.
zero


20.
A loop of wire carrying a current of 2.0 A is in the shape of a right triangle with two equal sides, each 15 cm long. A 0.7 T uniform magnetic field is in the plane of the triangle and is perpendicular to the hypotenuse. The resultant magnetic force on the two sides has a magnitude of:
A.
0
B.
0.21 N
C.
0.30 N
D.
0.41 N
E.
0.51 N


21.
A current is clockwise around the outside edge of this page and a uniform magnetic field is directed parallel to the page, from left to right. If the magnetic force is the only force acting on the page, the page will turn so the right edge:
A.
moves toward you
B.
moves away from you
C.
moves to your right
D.
moves to your left
E.
does not move


22.
The units of magnetic dipole moment are:
A.
ampere
B.
ampere ⋅meter
C.
ampere ⋅meter2
D.
ampere/meter
E.
ampere/meter2


23.
You are facing a loop of wire which carries a clockwise current of 3.0 A and which surrounds an area of 5.8 10−?2m2. The magnetic dipole moment of the loop is:
A.
3.0 A ⋅ m2, into the page
B.
3.0 A ⋅ m2, out of the page
C.
0.17 A ⋅ m2, into the page
D.
0.17 A ⋅ m2, out of the page
E.
0.17 A ⋅ m2, left to right


24.
A circular loop of wire with a radius of 20 cm lies in the xy plane and carries a current of 2 A, counterclockwise when viewed from a point on the positive z axis. Its magnetic dipole moment is:
A.
0.25 A ⋅ m2, in the positive z direction
B.
0.25 A ⋅ m2, in the negative z direction
C.
2.5 A ⋅ m2, in the positive z direction
D.
2.5 A ⋅ m2, in the negative z direction
E.
0.25 A ⋅ m2, in the xy plane


25.
For a loop of current-carrying wire in a uniform magnetic field the potential energy is a minimum if the magnetic dipole moment of the loop is:
A.
in the same direction as the field
B.
in the direction opposite to that of the field
C.
perpendicular to the field
D.
at an angle of 45° to the field
E.
none of the above


26.
The diagrms show five possible orientations of a magnetic dipole ± in a uniform magnetic field 4. For which of these is the potential energy the greatest?
A.
I
B.
II
C.
III
D.
IV
E.
V


27.
Suitable units for μ0 are:
A.
tesla
B.
newton/ampere2
C.
weber/meter
D.
kilogram⋅ampere/meter
E.
tesla⋅meter/ampere


28.
A "coulomb" is:
A.
one ampere per second
B.
the quantity of charge which will exert a force of 1 N on a similar charge at a distance of 1 m
C.
the amount of current in each of two long parallel wires separated by 1 m, which produces a force of 2 × 10–7 N per meter
D.
the amount of charge which flows past a point in one second when the current is 1 A
E.
an abbreviation for a certain combination of kilogram, meter and second


29.
Electrons are going around a circle in a counterclockwise direction as shown. At the center of the circle they produce a magnetic field that is:
A.
into the page
B.
out of the page
C.
to the left
D.
to the right
E.
zero


30.
The diagrams show three circuits consisting of concentric circular arcs (either half or quarter circles of radii r, 2r, and 3r) and radial lengths. The circuits carry the same current. Rank them according to the magnitudes of the magnetic fields they produce at C, least to greatest.
A.
1, 2, 3
B.
3, 2, 1
C.
1, 3, 2
D.
2, 3, 1
E.
2, 1, 3


31.
In an overhead straight wire, the current is north. The magnetic field due to this current, at our point of observation, is:
A.
east
B.
up
C.
north
D.
down
E.
west


32.
A wire carrying a large current i from east to west is placed over an ordinary magnetic compass. The end of the compass needle marked "N" will point:
A.
north
B.
south
C.
east
D.
west
E.
the compass will act as an electric motor, hence the needle will keep rotating


33.
The magnetic field a distance 2 cm from a long straight current-carrying wire is 2.0 ×105 T. The current wire is:
A.
0.16 A
B.
1.0 A
C.
2.0 A
D.
4.0 A
E.
25 A


34.
The magnetic field (in T) a distance 2 cm from a long straight wire carrying a current of 2 A is about:
A.
2 × 10–7
B.
1 × 10–5
C.
2 × 10–5
D.
1 × 10–3
E.
10


35.
Two long parallel straight wires carry equal currents in opposite directions. At a point midway between the wires, the magnetic field they produce is:
A.
zero
B.
non-zero and along a line connecting the wires
C.
non-zero and parallel to the wires
D.
non-zero and perpendicular to the plane of the two wires
E.
none of the above


36.
Two long straight wires are parallel and carry current in the same direction. The currents are 8.0 and 12 A and the wires are separated by 0.40 cm. The magnetic field in tesla at a point midway between the wires is:
A.
0
B.
4.0 × 10–4
C.
8.0 × 10–4
D.
12 × 10–4
E.
20 × 10–4


37.
Two long straight wires are parallel and carry current in opposite directions. The currents are 8.0 A and 12 A and the wires are separated by 0.40 cm. The magnetic field in tesla at a point midway between the wires is:
A.
0
B.
4.0 × 10–4
C.
8.0 × 10–4
D.
12 × 10–4
E.
20 × 10–4


38.
The diagram shows three equally spaced wires that are perpendicular to the page. The currents are all equal, two being out of the page and one being into the page. Rank the wires according to the magnitudes of the magnetic forces on them, from least to greatest.
A.
1, 2, 3
B.
2, 1 and 3 tie
C.
2 and 3 tie, then 1
D.
1 and 3 tie, then 2
E.
3, 2, 1


39.
Two parallel wires carrying equal currents of 10 A attract each other with a force of 1 mN. If both currents are doubled, the force of attraction will be:
A.
1 mN
B.
4 mN
C.
0.5 mN
D.
0.25 mN
E.
2 mN


40.
Two parallel wires, 4 cm apart, carry currents of 2 A and 4 A respectively, in the same direction. The force per unit length in N/m of one wire on the other is:
A.
1 × 10–3, repulsive
B.
1 × 10–3, attractive
C.
4 × 10–5, repulsive
D.
4 × 10–5, attractive
E.
none of these


41.
A constant current is sent through a helical coil. The coil:
A.
tends to get shorter
B.
tends to get longer
C.
tends to rotate about its axis
D.
produces zero magnetic field at its center
E.
none of the above


42.
If R is the distance from a magnetic dipole, then the magnetic field it produces is proportional to:
A.
R
B.
1/R
C.
R2
D.
1/R2
E.
1/R3


43.
A square loop of current-carrying wire with edge length a is in the xy plane, the origin being at its center. Along which of the following lines can a charge move without experiencing a magnetic force?
A.
x = 0, y = a/2
B.
x = a/2, y = a/2
C.
x = a/2, y = 0
D.
x = 0, y = 0
E.
x = 0, z = 0


44.
In Ampere's law, A4d´ = μ0i, the integration must be over any:
A.
surface
B.
closed surface
C.
path
D.
closed path
E.
closed path that surrounds all the current producing 4


45.
Two long straight wires enter a room through a window. One carries a current of 3.0 A into the room while the other carries a current of 5.0 A out. The magnitude in T⋅m of the path integral A4d´ around the window frame is:
A.
2.5 × 10–6 T ⋅ m
B.
3.8 × 10–6 T ⋅ m
C.
6.3 × 10–6 T m
D.
1.0 × 10–5 T m
E.
none of these


46.
If the magnetic field 4 is uniform over the area bounded by a circle with a radius R, the net current through the circle is:
A.
0
B.
2πRBμ0
C.
πR2B/μ0
D.
RB/2μ0
E.
2RB/μ0


47.
A long straight cylindrical shell carries current i uniformly distributed over its cross section. The magnitude of the magnetic field is greatest:
A.
at the inner surface of the shell
B.
at the outer surface of the shell
C.
inside the shell near the middle
D.
in hollow region near the inner surface
E.
near the center of the hollow region


48.
A long straight cylindrical shell has an inner radius Ri and an outer radius Ro. It carries a current i, uniformly distributed over its cross section. A wire is parallel to the cylinder axis, in the hollow region (r < Ri). The magnetic field is zero everywhere in the hollow region. We conclude that the wire:
A.
is on the cylinder axis and carries current i in the same direction as the current in the shell
B.
may be anywhere in the hollow region but must be carrying current i in the direction opposite to that of the current in the shell
C.
may be anywhere in the hollow region but must be carrying current i in the same direction as the current in the shell
D.
is on the cylinder axis and carries current i in the direction opposite to that of the current in the shell
E.
does not carry any current


49.
The magnetic field B inside a long ideal solenoid is independent of:
A.
the current
B.
the core material
C.
the spacing of the windings
D.
the cross-sectional area
E.
the direction of the current


50.
Solenoid 2 has twice the radius and six times the number of turns per unit length as solenoid 1. The ratio of the magnetic field in the interior of 2 to that in the interior of 1 is:
A.
2
B.
4
C.
6
D.
1
E.
1/3


51.
A solenoid is 3.0 cm long and has a radius of 0.50 cm. It is wrapped with 500 turns of wire carrying a current of 2.0 A. The magnetic field at the center of the solenoid is:
A.
9.9 × 10–8
B.
1.3 × 10–3
C.
4.2 × 10–2
D.
16 T
E.
20 T


52.
A toroid with a square cross section carries current i. The magnetic field has its largest magnitude:
A.
at the center of the hole
B.
just inside the toroid at its inner surface
C.
just inside the toroid at its outer surface
D.
at any point inside (the field is uniform)
E.
at none of the above


53.
A toroid has a square cross section with the length of an edge equal to the radius of the inner surface. The ratio of the magnitude of the magnetic field at the inner surface to the magnitude of the field at the outer surface is:
A.
1/4
B.
1/2
C.
1
D.
2
E.
4



STOP This is the end of the test. When you have completed all the questions and reviewed your answers, press the button below to grade the test.