Answer Key
Electromagnetism
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University:
College of Central Florida -
Course:
PHY-232 | College Physics II Academic year:
2021
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Views:
321
Pages:
24
Author:
Jamari Day
7. ELECTROMAGNETISM (~25%)
102 Multiple Choice Questions
Provincial)
(~7 questions on
17 Long Answer Problems (1 ½)
Answers:
Multiple Choice
1. c
2. c
3. d
4. a
5. b
6. d
7. d
8. b
9. c
10.a
11.c
12.d
13.d
14.b
15.c
16.c
17.d
18.c
19.b
20.a
21.c
22.a
23.a
24.b
25.d
26.b
27.a
28.c
29.d
30.c
31.b
32.a
33.d
34.c
35.d
36.a
37.b
38.c
39.c
40.a
41.b
42.b
43.c
44.b
45.b
46.d
47.d
48.d
49.a
50.a
51.a
52.b
53.c
54.b
55.d
56.b
57.b
58.d
59.d
60.d
61.c
62.c
63.a
64.b
65.b
66.c
67.b
68.c
69.d
70.b
71.d
72.c
73.d
74.c
75.a
76.a
77.d
78.c
79.b
80.a
81.a
82.b
83.b
84.d
85.c
86.b
87.c
88.d
89.a
90.a
91.b
92.c
93.d
94.c
95.b
96.d
97.b
98.d
99.c
100. c
101. d
102. c
Long Answers
1.
2.
3.
3.6
3.2 x 10-14 N
a) 2nd diagram
b) 3.2 x 10-2 A
b) 7.3
-2
x 10 m
4.
5.
6.
7.
8.
9.
10.
3.6 x 10-2 T
0.634 m
1.59 x 10-18 N
12.7 V
2.45 x 10-3 N
a) Step Down
11.
(b) 4.00 cm
12.
13.
b) 11 A
(a) 1.6 x 107 m/s
14.
15.
16.
1.4 x 10-3 m
not lit
a) 3.16
1.63 m/s
a) y to x
b) 112 V
17.
1
deflect Multiple Choice:
1. In which diagram below would the electron
experience no magnetic force upon entering
the field?
2. Which one of the following best describes
a step-up transformer? [primary circuit: p;
secondarycircuit: s]
3. A metal rod is resting on top of two 4.0 m long conducting rails that are separated by 1.8 m. The force of
friction between the rod and the rails is 1.2 N. A magnetic field of 5.2 102 T is directed upwards, as shown in
the diagram to the left.
How much current must be sent through
the rod before the rod begins to move and
in what direction will the rod move?
4. Four
identical pieces of wire are bent to form four different coils, each containing a
different number of loops. Each coil carries 5.0 A of current and is placed in the
same magnetic field of 0.2 T. Which of the four coils would experience the greatest
maximum torque?
5. A 0.10 m long solenoid, 3.0 102 m in diameter, has a total of 550 turns of wire. To produce a
1.2 102 T magnetic field at the centre of the solenoid, how much current must flow through the wire?
A. 0.26 A
B. 1.7 A
C. 9.5 x 102 A
D. 1.4 x 103 A
2 6. Four conductors of equal length are each
moved through a uniform magnetic field in
different directions and with different speeds,
as shown.
While the four conductors are being moved
through the field, in which conductor will the
largest potential difference be induced?
A. Conductor A
B. Conductor B
C. Conductor C
D. Conductor D
7. A 75-turn square coil of wire, 0.12 m on a side, is in a 4.5 102 T magnetic field. The field is perpendicular
to the coil. If the coil of wire is removed from the field in 0.10 s, what average emf is induced in the coil?
A. 6.5 103 V
B. 1.2 101 V
C. 2.4 101 V
D. 4.9 101 V
8. A bar magnet is dropped through a solenoid, as shown.
What is the direction of the induced current in the solenoid as the
magnet enters the top (i) and as the magnet leaves the bottom (ii)?
9. In the situation to the left, an electron is
moving at 1.9 107 m/s through crossed
electric and magnetic fields. When the
electric force is equal to the magnetic force,
as shown, the electron will travel in a straight
line.
If the magnetic field strength is 5.2 103 T. What must be the potential difference between the plates for the
electron to continue in a straight line?
A. 1.9 10–7 V
B. 3.9 10–5 V
C. 7.4 102 V
D. 4.7 103 V
3 10. Four compasses are placed around a conductor
carrying a current into the page, as shown to the
right. Which compass correctly shows the direction
of the magnetic field due to the current?
11.What is the radius of curvature of the path of a
proton travelling at 4. 7 105m/s in a plane
perpendicular to a 0.52 T magnetic field?
A. 2.0 x 10-8m
B. 5.1 x 10-6m
C. 9.4 x 10-3m
D. 1.1 x 102m
12. Two long, parallel conductors carry the same
current I and exert an attractive force F on each
other. If the current in both conductors is doubled,
what is the new force?
A. 0.5 F
B. 1 F
C. 2 F
D. 4 F
13. In the following diagram,
ammeter A shows a current
A. while switch S remains closed.
B. while switch S remains opened.
C. only while switch S is being
closed.
D. while switch S is being opened or
being closed.
14. A transformer connected to a 120 V ac source has an output of 24 V ac. If the primary coil has 330 turns,
how many turns of wire are there in the secondary coil?
A. 24 turns
B. 66 turns
C. 330 turns
D. 1650 turns
15. A 1 700 turn coil of radius 0.25 m, is located in a 0.085 T magnetic field. If the maximum torque on the coil
is 250 Nm, what current is in this coil?
A. 0.11 A
B. 6.9 A
C. 8.8 A
D. 28 A
16. A dc motor is connected to a constant voltage supply. The load on the motor decreases, allowing the motor
to rotate faster. How do the back emf and current through the motor change?
4 17. In which of the following situations would an induced emf be produced in a rectangular loop of wire? The
loop of wire is moved as indicated.
18. The graph to the left shows how the
magnetic flux through a single loop changes
with respect to time.
What is the average emf induced between
t 2.0 103 s and t 9.0 103 s?
A.
B.
C.
D.
1.2 104 V
1.8 V
3.6 V
25 V
19 Which of the following diagrams best represents the magnetic field in the region between north and south
poles of a pair of permanent magnets?.
5 20. A long conductor is placed in a 0.20 T magnetic field as shown in the diagram below.
What are the magnitude and direction of the magnetic force on the conductor when it carries a current of 12 A?
21. A 150 turn coil has an area of 2.4 104 m2 . What magnetic field strength will produce a maximum torque
of 2.2 103 Nm on the coil when a 0.20 A current flows through it?
A. 1.6 105 T
B. 0.13 T
C. 0.31 T
D. 3.3 T
22. A conductor is initially at rest in a magnetic field.
In which direction should the conductor be moved so that the
end nearest X becomes positive?
A. 1
B. 2
C. 3
D. 4
23. A coil of 150 turns and an area of 2.0 104 m2 is placed in a 1.00 T magnetic field as shown in
Diagram I.
If this field changes to 0.45 T in 0.060
what is the average emf induced in the
coil and in what direction does the
induced current flow?
s,
24. A dc motor has an armature
resistance of 3.0 . When connected to
24 V source the motor draws 1.4 A at
maximum speed. What is the back emf produced by the motor at maximum speed?
A. 4.2 V
B. 20 V
C. 24 V
D. 28 V
6
a 25. A soldering iron transformer has 200 primary turns and 5 secondary turns. The primary draws 0.80 A at
120V . Which of the following gives the secondary current and secondary voltage?
26. Which of the following are correct units for magnetic flux?
A. T
B. Wb
C. V/m
D. N m2
27. An electron enters a uniform magnetic field as shown
to the right.
The path of the electron upon entering this field would be
A. Linear
B. Circular
C. Parabolic
D. Hyperbolic
28. The diagram below represents a cross-sectional view from the side of a cathode ray tube. What is the
purpose of the coils in a functional cathode ray tube?
A. They increase the speed of the electrons
B. They focus the electrons into a fine beam
C. They deflect the electrons into or out of
the page
D. They deflect the electrons toward the top
or bottom of the page
29. A solenoid of length 0.35 m and diameter 0.040 m carries a current of 5.0 A through its windings. If the
magnetic field in the centre of the solenoid is 2.8 102 T, what is the number of turns per metre for this
solenoid?
A. 1.8 x 103 turns/m B. 7.8 x 103 turns/m C. 1.6 x 103 turns/m
D. 4.5 x 103 turns/m
30. A 1.2 m length of wire is pulled through a uniform
0.045 T magnetic field at 6.7 m/s as shown. What emf is
generated between the ends of the wire?
A. 0 V
B. 0.090 V
C. 0.36 V
D. 0.45 V
31. A dc motor is connected to a 12.0 V power supply. When the armature is rotating, the current through it is
0.78 A and the back emf is 10.6 V. What is the resistance of the armature?
A. 1. 4
B. 1.8
C. 14
D. 15
7 32. In which of the following diagrams is the secondary current greater than the primary current?
33. An electron circulates in a uniform 5. 0 104 T magnetic field as shown. If
the electron has 3.2 1018 J of kinetic energy, what is its radius of orbit, r ?
A. 2.3 x 10-7 m
B. 4.6 x 10-4 m
C. 2.5 x 10-3 m
D. 3.0 x 10-2 m
34. A compass is placed in each of the four locations around a permanent bar magnet as shown below.
In which location would the North pole of the compass needle point to the right side of the page?
A. Location 1
B. Location 2
C. Location 3
D. Location 4
35. A square coil is perpendicular to a uniform magnetic field. Which one of the following would increase the
magnetic flux through the coil?
A. Decreasing the area of the coil.
B. Increasing the number of loops in the coil.
C. Removing the coil from the magnetic field.
D. Increasing the strength of the magnetic field.
36. A charge X is placed in an electric field and a second charge Y is placed in a magnetic field. If both charges
are initially held at rest, which one of the following best describes the motion of the charges after they are
released? (Ignore gravitational effects.)
A. Charge X accelerates.
B. Charge Y accelerates.
C. Both charge X and charge Y accelerate. D. Neither charge X nor charge Y accelerates.
37. Two straight parallel wires are separated by 1.60 m. The first wire carries a current of 95.0 A, and the
magnetic field produced by this current exerts a force of 2.50 x 10–3 N on a 2.00 m length of the second wire.
What is the current in the second wire?
A. 20.9 A
B. 105 A
C. 132 A
D. 164 A
38. A coil of wire of area 1.5 x 10–3 m2 consists of 40 loops. A magnetic field is perpendicular to the face of the
coil. In a period of 0.20 s the strength of the magnetic field decreases from 0.060T to0.050T in the same
direction. What is the average emf induced in the coil during this time?
A. 7.5 x 10–5 V
B. 1.5 x 10–3 V
C. 3.0 x 10–3 VD. 3.3 x 10–2 V
8 39. The current in an electric motor running at full speed is 2.5 A when connected to an 80 V dc source. If the
armature resistance of the motor is 4.0 , what is the back emf at this speed?
A. 0 V
B. 10 V
C. 70 V
D. 90 V
40. An ideal transformer has 150 turns in the primary coil and 1 800 turns in the secondary coil. If the primary
coil is connected to 120 V ac and draws 7.5 A of current, what is the current in the secondary coil?
A. 0.63 A
B. 7.5 A
C. 16 A
D. 90 A
41. An electron moves in a circular orbit of radius r in a magnetic field. The electron moves in a path
perpendicular to the magnetic field. If the kinetic energy of the electron is doubled, what is the new radius of its
path?
42. Which of the following correctly shows the magnetic field between two opposite, magnetic poles?
43. A proton moving parallel to a current-carrying wire (see diagram
to the right) will experience a force in what direction? (The proton
and the wire are both in the plane of the page.)
A.
B.
C.
D.
into the page
out of the page
toward the conductor (to the right)
away from the conductor (to the left)
44. A particle with a charge of 3.2 1019 C is moving at 1.2 106m/s. This particle enters a 0.25T magnetic
field at right angles and travels in a circular path of 0.80m radius. What is the mass of this particle?
A. 6.7 10 27 kg
B. 5.3 10 26 kg
C. 6.4 10 20 kg
D. 7.7 10 14 kg
9 45. Which of the following is a statement of Lenz’s law?
A. The number of magnetic lines perpendicular to the surface area enclosed by a circuit is equal to the flux.
B. An induced current in a closed conducting loop will appear in such a direction that it opposes the change that
created it.
C. An emf is produced between the ends of a straight wire when the wire is moving perpendicularly through a
uniform magnetic field.
D. The average emf induced in a circuit is proportional to the rate of change of the magnetic flux through that
circuit.
46. A 2.5 m wire moves 77 m/s perpendicular to a uniform 3.8 106 T magnetic field. What potential
difference is induced across the ends of this wire?
A. 0 V
B. 1.6 1019 V
C. 2.0 108 V
D. 7.3 104 V
47. A transformer has four times as many turns on the secondary as on the primary. If the primary voltage is
120 V ac, which of the following describes the transformer?
48. Which of the following diagrams shows the magnetic field produced by a long
current-carrying wire?
49. The diagram below shows an electron travelling to the left in a magnetic field.
In which direction will the electron be deflected?
A. into the page
B. out of the page
C. towards the north pole
D. towards the south pole
10 50. A doubly-ionized atom (Q = 2e) with a mass of 6.8 1027 kg enters a 3.0 T magnetic field with a speed of
5.0 107 m/s. What is the radius of the circular path of the atom?
A. 0.35 m
B. 0.71 m
C. 1.4 m
D. 2.8 m
51. A wire is in a magnetic field as shown.
In which direction could the wire be moved to induce an
emf across the length of the wire?
A. to the left
B. up the page
C. into the page
D. down the page
52. An emf is induced in a coil if the magnetic flux through the coil is
A. zero.
B. changing.
C. constant and large. D. constant and small.
53. A coil of wire contains 55 loops. The coil is rotated such that the flux changes from 2.0 104 Wb to
8.0 10 4 Wb in 1.5 102 s. What is the average induced emf?
A. 1.1 V
B. 1.8 V
C. 2.2 V
D. 3.7 V
54. A door bell transformer has 900 primary windings and 60 secondary windings. The secondary current is
0.30 A. What is the primary current and what is the type of transformer?
55. In the diagram below, what is the direction of the magnetic field at point P due to the bar magnet?
A. up the page
B. down the page
C. towards the left
D. towards the right
56. An ion with a charge of 1.6 1019 C enters a 0.075 T magnetic field. If the ion follows a circular path of
radius 0.083 m, what is the momentum of the ion?
A. 2.7 1026 kg m/s
B. 1.0 1021 kg m/s
C. 1.7 1012 kg m/s D. 5.2 104 kg m/s
57. A long straight wire is carrying a 70 A current. What is the magnitude of the magnetic field due to this
current at a point 0.15 m from the wire?
A. 8.8 105 T
B. 9. 3 105 T
C. 5. 9 104 TD. 6. 2 104 T
11 58. Which of the following describes a possible step-up transformer?
59. A 525-turn solenoid has a diameter of 0.050 m and a length of 0.20 m. What current is needed to produce a
0.025 T field inside the solenoid?
A. 0.38 A
B. 1.9 A
C. 3.8 A
D. 7.6 A
60. The flux through a 240 turn coil changes by 4.0 102 Wb in 0.20 s. What is the magnitude of the average
emf induced in the coil during this time?
A. 1.9 V
B. 9.6 V
C. 24 V
D. 48 V
61. Two solenoids S1 and S2 are placed close together as shown in the diagram below.
Immediately after the switch is closed, what is the direction of current flow through galvanometer G and what is
the direction of the magnetic field produced by this current at position P inside solenoid S2?
62. Which of the following diagrams
to the right best shows the magnetic
field lines between the poles of two
permanent magnets?
12 63. A 0.15m wire carrying 12 A of current to the right is placed in a magnetic field coming out of the page of
strength 0.63 T. What are the magnitude and direction of the magnetic force acting on the wire?
64. A particle having a charge of 3. 2 1019 C follows a circular path of 0.45 m radius while travelling at a
speed of 1.2 104 m/s in a 0.78 T magnetic field. What is the mass of the particle?
A. 7.8 1028 kg
B. 9.4 1024 kg
C. 1.11019 kg
D. 3.0 1015 kg
65. A 460-turn solenoid having a diameter of 0.024 m is 0.14 m long. What is the magnetic field at the centre of
the solenoid when a 13 A current flows through it?
A. 0 T
B. 5.4 102 T
C. 3.1 101 T
D. 6.3 101 T
66. A conducting rod is moving perpendicular to a
uniform magnetic field of 0.23 T at a velocity of 9.2 m/s .
What emf is generated during this motion?
A. 0 V
B. 0. 025 V
C. 0. 32 V
D. 0. 53 V
67. A rectangular coil measuring 0.12 m by 0.080 m is placed
perpendicular to a 0.85 T
magnetic field as shown.
What is the magnetic flux through the coil?
A. 0 Wb
B. 8. 2 10 3 Wb
C. 6.8 10 2 Wb
D. 1. 0 10 1 Wb
13 68. A single loop of wire of radius
0.23 m is placed in a 0.75 T
magnetic field as shown. The
magnetic field is changed to a
strength of 0. 50 T in the opposite
direction in 0.61 s.
What is the average emf induced in
the coil?
A. 0. 068 V
B. 0. 094 V
C. 0. 34 V
D. 0. 47 V
69. With the electromagnet turned off, electrons in a cathode ray tube strike the centre of the screen as shown.
When the electromagnet is turned on,
where will the electron beam now
strike the screen?
A. 1
B. 2
C. 3
D. 4
70. A compass is positioned at each of the following locations near a bar magnet.
In which location will the compass needle point to the right-hand side of the page?
A. 1
B. 2
C. 3
D. 4
71. A current-carrying conductor is placed in a uniform magnetic field as shown.
What is the direction of the magnetic force on this conductor?
A. Into the page
B. Out of the page
C. Towards the top of the page
D. Towards the bottom of the page
14 72. A 5.0 A current flows through a 0. 20 m long solenoid that contains 1 500 loops.
What are the magnitude and direction of the magnetic field at the centre of the solenoid?
73. Four conductors of different lengths are moved through a uniform magnetic field at the same speed.
Which conductor will induce the greatest
emf?
1
2
3
4
A.
B.
C.
D.
74. A motor has an armature resistance of 3.5 and is connected to a 12. 0 V source. At full speed the current
through the armature is 0.18 A. What is the back emf at full speed?
A. 0 V
B. 0. 63 V
C. 11. 4 V
D. 12. 0 V
75. A step-down transformer has a 500 turn
primary that operates at 120 V ac. Which of the
following sets of conditions best describes the
number of secondary turns and secondary voltage
of this transformer?
15 76. A flexible loop of wire of area
4.5x10-2m2 is positioned in a 0.17 T
magnetic field as shown in Figure A.
The loop is then stretched until its
area is zero in a time of 0.35s (Figure
B). What is the average induced emf
in the circuit and the direction of the
current through Resistor R?
77. Which of the following is a step-up transformer?
78. A solenoid of diameter 0.018 m is 0.30 m long. A current of 5.3 A is used to create a magnetic field of 0.25
T at the centre of the solenoid. How many turns of wire does this solenoid have?
A. 6.8 102
B. .1x 103
C. 1.110 4
D. 3.8 104
79. A beam of electrons is directed into a uniform magnetic field and deflects as shown in Figure I. If a beam of
protons with the same
speed were to enter this
same magnetic field, which
of the paths shown in
Figure II would the protons
take?
A. 1
B. 2
C. 3
D. 4
16 80. Which of the following graphs best
shows how the magnetic field B varies
with the perpendicular distance d from
a long, straight current-carrying
conductor?
81. For what type of input current will
the output current in a transformer be
zero?
A. dc
B. ac
C. increasing dc
D. decreasing dc
82. A motor designed to operate on 120 V draws a current of 33 A when it first starts up. At its normal
operating speed, the motor draws a current of 2.7 A. What is the back emf at normal operating speed?
A. 9.8 V
B. 110 V
C. 120 V
D. 130 V
83. A 35 loop square coil 0.12 m on a side is positioned in a 0.050 T magnetic field. A 0.20 kg mass is
suspended from one side of the coil as shown in the diagram below.
How much current must pass through the coil in order for the coil to remain horizontal?
A. 2.3 A
B. 4.7 A
C. 9.3 A
D. 330 A
84. The magnetic field around a current-carrying wire is investigated with a compass.
At which of the four positions shown in the diagram will the
compass needle point towards the bottom of the page?
A. 1
B. 2
C. 3
D. 4
85. When a 15.0 A current flows through a 0.120 m long solenoid, the magnetic field along its center is
8.00 10 2 T. How many turns make up this solenoid?
A. 23
B. 162
C. 509
D. 4 240
86. A coil of wire has an area of 2. 5 10–3 m2 . What is the magnetic flux through this coil when its plane is
perpendicular to a 0.75 T magnetic field?
A. 0 Wb
B. 1. 9 10–3 Wb
C. 3. 3 10–3 Wb
D. 0. 75 Wb
87. A dc motor has an armature resistance of 1.5 . When running at full speed, the motor draws a current of
2.0 A from a 16 V source. What is the back emf at this speed?
A. 0 V
B. 3 V
C. 13 V
D. 16 V
17 88. In order to induce an emf in a coil, the magnetic flux must be
A. zero.
B. small.
C. large.
D. changing.
89. Charged particles J and K enter a magnetic field as show in the diagram below.
Particle J travels in a circular path of radius r. Particle K has twice the charge and half the momentum of
particle J. How does the radius of particle K’s path compare to that
of particle J?
A. 1/4 r
B. r
C. 2r
D. 4r
90. A transformer is used to reduce the house supply (120 V ac) to
operate a small toy that requires 9.0 V ac at 0.240 A. Which of the following gives the primary current and
possible values for primary and secondary windings?
91. Which of the following shows the magnetic field produced by a current carrying conductor?
92. A 0.20 m conductor moves at 12 m/s through the 0.60 T field shown below. Calculate the emf induced in
the conductor while passing through the field.
A. 0 V
B. 0.13 V
C. 1.4 V
D. 1.8 V
18 93. A coil has 680 turns of wire, a current
of 5.6 A, and an area of
2.1 102 m2 . This coil is placed in a 0.22
T magnetic field in either field-coil
orientation X or Y.
Which field-coil orientation would produce
a maximum torque, and what is the
magnitude of this torque?
94. Which of the following shows a coil having the largest flux?
95. When the coil of a motor is rotating at maximum speed, the current in the windings is 3.3 A. When the
motor is first connected to 120 V, the current in the windings is 12 A. What is the back emf in the coil at
maximum speed?
A. 33 V
B. 87 V
C. 110 V
D. 120 V
96. An ideal transformer has 3 000 turns on its
primary winding and 150 turns on its secondary
winding. The primary is connected to 120 V ac. If
0.20 A is drawn from the secondary, what is the
primary current and the secondary voltage?
97. In a step-up transformer, how does the secondary voltage
V s compare with the primary voltage V p , and the number of
turns in the secondary N s compare with the number of turns
in the primary N p ?
19 98. Two particles Y and Z with equal mass
and speed enter a uniform magnetic field
and follow the paths as shown. How do
their magnitude and polarity of charge
compare?
99. A wire carrying a current of 5. 0 A is in a
uniform 3.2 102 T magnetic field as shown to
the right. What is the force on the 0.15 m length
wire?
A. 0 N
B. 1. 6 102 N
of
C. 2. 4 102 N
D. 4. 0 102 N
100. A single coil of wire of area 6.0 103 m2 is positioned in a uniform 0.18 T magnetic field as shown. The
coil is rotated 90about axis XY in 4.2 103 s. What average emf is induced by the coil?
A. 0 V
B. 0.13 V
C. 0.26 V
D. 43 V
101. A part of a coil of wire is placed in a uniform magnetic field as shown. Which two directions of motion
would immediately induce an emf in the coil?
A. 1 and 2
B. 1 and 3
C. 2 and 3
D. 2 and 4
20 102. An electric motor is connected to a constant source of potential. Considering back emf, which of the
following observations is correct?
A. At full speed the applied voltage increases.
B. At full speed the armature resistance increases.
C. If the motor is kept from rotating at full speed, the armature heats up.
D. If the motor is kept from rotating at full speed, the armature temperature decreases.
Written Problems:
1. A motor is connected to 117 V and draws a current of 32.5 A when it first starts up. At its normal operating
speed, the motor draws a current of 4.20 A.
What is the resistance of the armature coil? (3 marks)
2. A 0.400 m long solenoid has 6 720 turns of wire. A current of 14.5 A flows in the solenoid. An electron
inside the solenoid travels perpendicular to the axis of the solenoid with a speed of 6. 50 105 m/s . What is the
magnitude of the magnetic force acting on the electron? (7 marks)
3. A beam of electrons travelling at 1.8 108 m/s is directed towards a 0.014 T magnetic field as shown in the
diagram below.
a) Which of the following diagrams illustrates the path of the electron beam once in the
magnetic field? (Circle one.) (1 mark)
b) What is the radius of the path of the electron beam while in the magnetic field? (6 marks)
21 4. A single loop of wire of area 5. 0 3 m 2 and resistance 1.is perpendicular to a uniform magnetic field
B. The field then decreases to zero in 1. 23 s inducing an average current of 8.3 102 A in the loop. What
was the initial value of the magnetic field B? (7 marks)
5. A proton with a speed of 1.30 x 103 m/s travels parallel to a horizontal wire carrying a current of 2.50 x 10–4
A as shown.
If the magnetic force on the proton is 1.64 x 10–26 N, at what distance d is the proton traveling above the wire?
(7 marks)
6. A proton is traveling at 2.58 105 m /s towards a conductor carrying a current of 125 A. What is the
magnitude of the magnetic force acting on the proton 0.650 m from the conductor? (7 marks)
7. When an electric drill turns at normal operating speeds, there is little heat produced in the motor windings.
When drilling harder material, the drill motor turns much slower than normal and overheats. Using principles of
physics, give an explanation for the increased heat in the windings. (4 marks)
8.a) A 16.0 V power supply is used to run a dc motor. When the motor is jammed so that it cannot turn, it draws
a current of 12.0 A. What is the back or counter emf when the motor runs freely, drawing a current of 2.50 A?
(5 marks)
b) Using principles of physics, explain why the motor draws a much higher current when jammed than when
running freely. (4 marks)
9. The diagram below shows a 650-turn solenoid carrying a 4.0 A current.
What is the magnitude of the magnetic force on the 0.015 m segment of wire carrying a 6.0 A current inside the
solenoid as shown? (7 marks)
22 10. An electric device operates on 9. 0 V ac and has a total resistance of 21 . An ideal
transformer is used to change the incoming line voltage of 120 V ac to the operating voltage of 9.0 V ac.
a) Is the transformer a step-up or step-down transformer? (1 mark)
b) What is the current in the primary side? (6 marks)
11. An electron is accelerated from rest through a potential difference of 750 V. It then enters a uniform
2.3 103 T magnetic field at right angles to the field.
a) What is the speed of the electron? (3 marks)
b) What is the radius of its path in the magnetic field? (4 marks)
12. A solenoid of length 0.85 m has a radius of 0.10 m . A current of 25 A flows through its 7 600 turns. Within
this solenoid, a 0.12 m wire moves as shown and develops an emf of 0.055 V across its ends.
With what speed does the wire move perpendicular to the solenoid’s magnetic field? (7 marks)
13. 6. A 0.025 m wire segment is positioned in a 0.75 T magnetic field as shown in the diagram below. When a
current is passed through this wire segment it experiences a 0.20 N force upwards.
a) What is the direction of the current? (Circle one.) (2 marks)
From X to Y
From Y to X
b) What is the magnitude of the current? (5 marks)
14. Electrons accelerated from rest through a potential difference of 300 V enter a 4.1 10 2 T magnetic field
at right angles. What is the radius of curvature of the path taken by the electrons? (7 marks)
23 15. An ideal transformer is connected to a 12 V ac power supply. The light bulb connected to the secondary of
the transformer is lit (Figure A). The transformer is then connected to a 12 V dc battery (Figure B).
a) The bulb will (check one response) (1 mark)
b.) b) Using principles of physics, explain your answer to a). (3 marks)
16. A motor is connected to a constant 120 V source and draws a current of 38. 0 A when it first starts up. At its
normal operating speed, the motor draws a current of 2. 50 A.
a.) What is the resistance of the armature coil? (3 marks)
b) What is the back emf at normal speed? (4 marks)
17. a) In a cathode ray tube, the purpose of the coils is to
b) Using the principles of electromagnetism, explain how this effect on the electrons is
achieved by the coils. (3 marks)
24
Electromagnetism
of 24
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