Download ExamView - Magnetism

Magnetism
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1. An electron which moves with a speed of 3.0  104 m/s parallel to a uniform magnetic field of 0.40 T
experiences a force of what magnitude? (e = 1.6  1019 C)
a. 4.8  1014 N
c. 2.2  1024 N
15
b. 1.9  10 N
d. zero
____
2. 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?
a. zero
c. 90°
b. 180°
d. 45°
____
3. 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?
a. out of the page
c. to the left
b. to the right
d. into the page
____
4. A proton moves across the Earth’s equator in a northeasterly direction. At this point the Earth’s magnetic field
has a direction due north and is parallel to the surface. What is the direction of the force acting on the proton
at this instant?
a. toward the northwest
c. into the Earth’s surface
b. out of the Earth’s surface
d. toward the northeast
____
5. The right-hand rule allows one to find a property of the interaction of a magnetic field with a charged particle.
The right-hand rule applied to moving charges:
a. results in positive charges moving
c. can be used for positive charges only.
clockwise.
b. results in negative charges moving
d. gives the direction of the force on a
clockwise.
charge moving in a magnetic field.
____
6. Different units can be used to measure the same physical quantity, differing only by some multiplicative
factor. The cgs unit for magnetic field, the gauss, is equal to ________ tesla.
a. 104
c. 0.5
d. These units do not measure the same
b. 10-4
physical quantity.
____
7. A stationary positive charge +Q is located in a magnetic field B, which is directed toward the right as
indicated. The direction of the magnetic force on Q is:
a.
b.
____
toward the right.
up.
c.
d.
down.
There is no magnetic force.
8. The direction of the force on a current carrying wire located in an external magnetic field is which of the
following?
a. perpendicular to the current
c. Both choices A and B are valid.
b. perpendicular to the field
d. None of the above are valid.
1
____
9. A circular current loop is placed in an external magnetic field. How is the torque related to the radius of the
loop?
a. directly proportional to radius
c. directly proportional to radius squared
b. inversely proportional to radius
d. inversely proportional to radius squared
____ 10. The path of a charged particle moving parallel to a uniform magnetic field will be a:
a. straight line.
c. ellipse.
b. circle.
d. parabola.
____ 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:
a. energy.
c. radius for the circle.
b. momentum.
d. time to go around the circle once.
____ 12. The current in a long wire creates a magnetic field in the region around the wire. How is the strength of the
field at distance r from the wire center related to the magnitude of the field?
a. field directly proportional to r
c. field directly proportional to r2
b. field inversely proportional to r
d. field inversely proportional to r2
____ 13. A current in a long, straight wire produces a magnetic field. The magnetic field lines:
a. go out from the wire to infinity.
c. form circles that pass through the wire.
b. come in from infinity to the wire.
d. form circles that go around the wire.
____ 14. Two parallel wires are separated by 0.25 m. Wire A carries 5.0 A and Wire B carries 10 A, both currents in
the same direction. The force on 0.80 m of Wire A is:
a. half that on 0.80 m of wire B.
c. toward Wire B.
b. one-fourth that on 0.80 m of wire B.
d. away from Wire B.
____ 15. A current in a solenoid coil creates a magnetic field inside that coil. The field strength is directly proportional
to:
a. the coil area.
c. Both A and B are valid choices.
b. the current.
d. None of the above choices are valid.
____ 16. 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:
a. number of turns in the loop.
c. Both choices A and B are valid.
b. current strength.
d. None of the above are valid.
____ 17. When an electromagnet has an iron core inserted, what happens to the strength of the magnet?
a. It increases.
c. It decreases.
b. It remains the same.
d. Since it depends on the metal used in the
wires of the electromagnet, any of the
above.
____ 18. 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?
a. out of the page
c. from bottom edge to top edge of the page
b. into the page
d. from right to left across the page
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____ 19. A proton is released such that it has an initial speed of 4.0  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  1019 C)
a. 4.8  1025 N
c. 3.8  1014 N
19
b. 1.3  10 N
d. 7.5  103 N
____ 20. A proton moving at a speed of 3.8  106 m/s cuts across the lines of a magnetic field at an angle of 70°. The
strength of the field is 0.25  104 T. What is the magnitude of the force acting on the proton? (qp = 1.6 
1019 C)
a. 5.1  1018 N
c. 1.4  1017 N
18
b. 9.0  10 N
d. 2.3  1017 N
____ 21. An electron moves through a region of crossed electric and magnetic fields. The electric field E = 2 000 V/m
and is directed straight down. The magnetic field B = 0.80 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?
a.
b.
2 500 m/s
4 000 m/s
c.
d.
5 000 m/s
8 000 m/s
____ 22. A proton and a deuteron are moving with equal velocities perpendicular to a uniform magnetic field. A
deuteron has the same charge as the proton but has twice its mass. The ratio of the magnetic force on the
proton to that on the deuteron is:
a. 0.5.
c. 2.
b. 1.
d. There is no magnetic force in this case.
____ 23. A proton and a deuteron are moving with equal velocities perpendicular to a uniform magnetic field. A
deuteron has the same charge as the proton but has twice its mass. The ratio of the acceleration of the proton
to that of the deuteron is:
a. 0.5.
c. 2.
b. 1.
d. There is no acceleration in this case.
____ 24. 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?
a. 6.7 N
c. 0.15 N
b. 0.30 N
d. zero
____ 25. A copper wire of length 25 cm is in a magnetic field of 0.20 T. If it has a mass of 10 g, what is the minimum
current through the wire that would cause a magnetic force equal to its weight?
a. 1.3 A
c. 2.0 A
b. 1.5 A
d. 4.9 A
3
____ 26. 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?
a. 0.60 T
c. 1.8  10-3 T
b. 1.5 T
d. 6.7  10-3 T
____ 27. 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 Earth's magnetic field is due north at this point and has a strength of 0.14  104 T. What is the
size of the force on the wire?
c. 1.9  104 N
a. 0.28  104 N
4
b. 2.5  10 N
d. 1.6  104 N
____ 28. A wire is lying horizontally in the north-south direction and the horizontal magnetic field is toward the east.
Some positive charges in the wire move north and an equal number of negative charges move south. The
direction of the force on the wire will be:
a.
b.
east.
down, into the page.
c.
d.
up, out of the page.
There is no magnetic force.
____ 29. A circular loop carrying a current of 1.0 A is oriented in a magnetic field of 0.35 T. The loop has an area of
0.24 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?
a. 5.8 Nm
c. 0.084 Nm
b. 0.68 Nm
d. 0.017 Nm
____ 30. 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:
a.
b.
2ILB.
ILB.
c.
d.
IBL2.
zero.
____ 31. A proton moving with a speed of 3.0  105 m/s perpendicular to a uniform magnetic field of 0.20 T will
follow which of the paths described below? (qp = 1.6  1019 C and mp = 1.67  1027 kg)
a. a straight line path
c. a circular path of 3.1 cm radius
b. a circular path of 1.6 cm radius
d. a circular path of 0.78 cm radius
4
____ 32. A deuteron, with the same charge but twice the mass of a proton, moves with a speed of 3.0  105 m/s
perpendicular to a uniform magnetic field of 0.20 T. Which of the paths described below would it follow? (qp
= 1.6  1019 C and md = 3.34  1027 kg)
a. a straight line path
c. a circular path of 3.1 cm radius
b. a circular path of 1.6 cm radius
d. a circular path of 0.78 cm radius
____ 33. A proton, which moves perpendicular to a magnetic field of 1.2 T in a circular path of radius 0.080 m, has
what speed? (qp = 1.6  1019 C and mp = 1.67  1027 kg)
a. 3.4  106 m/s
c. 9.6  106 m/s
b. 4.6  106 m/s
d. 9.2  106 m/s
____ 34. 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 path 3.43
cm in radius. What is the ratio of the two isotope masses, mX/mY?
a. 0.977
c. 1.05
b. 1.02
d. 0.954
____ 35. In a mass spectrometer, an ion will have a smaller radius for its circular path if:
a. its speed is greater.
c. its charge is greater.
b. its mass is greater.
d. the magnetic field is weaker.
____ 36. At the Fermilab accelerator in Weston, Illinois, singly-charged ions with momentum 4.8  1016 kgm/s are
held in a circular orbit of radius 1 km by an upward magnetic field. What B-field must be used to maintain the
ions in this orbit? (qion = 1.6  1019 C)
a. 1 T
c. 3 T
b. 2 T
d. 4 T
____ 37. A proton with initial kinetic energy E is moving in circular motion in a uniform magnetic field. When it has
completed one eighth of a revolution, what is its kinetic energy?
a. 1.4 E
c. E
b. 0.71 E
d. The value is not given.
____ 38. 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 0.050 m from the wire? (magnetic permeability in empty space µ0 = 4  107 Tm/A)
a. 4.0  105 T
c. 1.6  105 T
b. 2.0  105 T
d. zero
____ 39. A superconducting wire carries a current of 10 4 A. Find the magnetic field at a distance of 1.0 m from the
wire. (µ0 = 4  107 Tm/A)
a. 2  103 T
c. 1.6  102 T
b. 8  103 T
d. 3.2  102 T
____ 40. A high-voltage power line 20 m above the ground carries a current of 2 000 A. What is the magnetic field due
to the current directly underneath the power line? (µ0 = 4  107 Tm/A)
a. 20 µT
c. 14 mT
b. 35 µT
d. 0.30 T
5
____ 41. Two long parallel wires 40 cm apart are carrying currents of 10 A and 20 A in the same direction. What is the
magnitude of the magnetic field halfway between the wires?
a. 1.0  10-5 T
c. 3.0  10-5 T
-5
b. 2.0  10 T
d. 4.0  10-5 T
____ 42. Two long parallel wires 40 cm apart are carrying currents of 10 A and 20 A in the opposite direction. What is
the magnitude of the magnetic field halfway between the wires?
c. 3.0  10-5 T
a. 1.0  10-5 T
b. 2.0  10-5 T
d. 4.0  10-5 T
____ 43. Two parallel conductors are carrying currents in the same direction. The currents are non-zero and not
necessarily equal. The magnitude of the magnetic field midway between them is 40 T. If one of the currents
then has its direction reversed, what is the resulting magnitude of the magnetic field midway between them?
a. a value greater than 40 T
c. a value less than 40 T
b. 40 T
d. It could be any value.
____ 44. Two parallel conductors are carrying currents in the opposite direction. The currents are non-zero and not
necessarily equal. The magnitude of the magnetic field midway between them is 40 T. If one of the currents
then has its direction reversed, what is the resulting magnitude of the magnetic field midway between them?
a. a value greater than 40 T
c. a value less than 40 T
b. 40 T
d. It could be any value.
____ 45. Two parallel conductors each of 0.50 m length, separated by 5.0  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
µ0 = 4  107 Tm/A)
a. attractive, 0.06  104 N
c. attractive, 1.8  104 N
b. repulsive, 0.60  104 N
d. repulsive, 1.8  104 N
____ 46. Consider two long, straight parallel wires, each carrying a current I. If the currents are flowing in opposite
directions:
a. the two wires will attract each other.
c. the two wires will exert a torque on each
other.
b. the two wires will repel each other.
d. neither wire will exert a force on the
other.
____ 47. Two parallel wires are separated by 0.25 m. Wire A carries 5.0 A and Wire B carries 10 A, both currents in
the same direction. The force on 0.80 m of Wire A is:
c. 1.6  10-5 N.
a. 3.2  10-5 N.
b. 2.6  10-5 N.
d. less than 1.0  10-5 N.
____ 48. 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 µ0 = 4  107 Tm/A)
a. 31  104 T
c. 125  104 T
4
b. 62  10 T
d. 250  104 T
____ 49. Superconductors can carry very large currents with no resistance. If a superconducting wire is formed into a
solenoid of length 50.0 cm with 500 turns, what is the magnetic field inside the solenoid when the current is
104 A? (µ0 = 4  107 Tm/A)
a. 1.25 T
c. 6.28 T
b. 2.50 T
d. 12.6 T
6
____ 50. A superconducting solenoid is to be designed to generate a magnetic field of 5.00 T. If the solenoid winding
has 1 000 turns/m, what is the required current? (µ0 = 4  107 Tm/A)
a. 1 000 A
c. 3 980 A
b. 1 990 A
d. 5 000 A
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ID: A
Magnetism
Answer Section
MULTIPLE CHOICE
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
21.
22.
23.
24.
25.
26.
27.
28.
29.
30.
31.
32.
33.
34.
35.
36.
37.
38.
39.
40.
D
C
B
B
D
B
D
C
C
A
B
B
D
C
B
C
A
B
C
C
A
B
C
D
C
A
D
B
C
C
B
C
D
A
C
C
C
C
A
A
1
ID: A
41.
42.
43.
44.
45.
46.
47.
48.
49.
50.
A
C
A
C
D
B
A
D
D
C
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