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Physics 112
Exam 2
Summer 2006
Name_________________
Physics 112
Summer 2006
Exam 2
Monday, July 10
Directions:
This 60-minute exam consists of twenty multiple-choice questions. This test is worth
20% of your final grade. (One point is equal to 1% of the final grade.)
The questions on this test are not in order of difficulty.
You must mark all of your answers on both your test and answer sheet.
In marking the multiple choice bubble sheet use a number 2 pencil. Do not use ink. If
you did not bring a pencil, ask for one. Fill in the appropriate circles completely. If you
need to change any entry, you must completely erase your previous entry.
Carefully read each question and its five possible answers. Select one and only one
answer for each question. Choose the answer that is closest to the correct one.
You have a sheet in the back of the test that you may use for any extra rough work.
When you are finished with the exam, place all exam materials, including the bubble
sheet, the exam itself, and scratch paper that you used for the exam, in your folder and
return the folder.
Good luck!
Page 1 of 8
Physics 112
Exam 2
Summer 2006
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21. Positive charge q is moving with velocity v in the magnetic field B as shown below


(with vectors v and B on the surface of the page). What is the direction of the magnetic
force?

v
q


A) Parallel to v

B) Parallel to B


C) Exactly between v and B
D) Into the page
E) Out of the page

B
22. A positively charged particle is moving in a magnetic field. What is the angle
between the velocity of the charge and the direction of the magnetic field if the magnetic
force on the particle is zero?
A) 90°
B) 45°
C) 30°
D) 0
E) Magnetic force can not be zero if the speed of the particle and the magnetic field are
not zero.
23. Alpha particles of charge q  2e and mass m  6.6  10 27 kg are emitted from a
radioactive source at a speed of 1.6 107 m s . What magnetic field strength would be
required to bend them into a circular path of radius r  0.25 m?
A) 5.3 T
B) 4.3 T
C) 3.3T
D) 2.3 T
E) 1.3 T
24. If a bar magnet is divided into two equal pieces,
A) the north and south poles are separated
B) two magnets result
C) the magnet properties are destroyed
D) an electric field is created
E) non of the above
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Physics 112
Exam 2
Summer 2006
25. An electric field of 1.60 kV/m and magnetic field of 0.400 T act on a moving electron
to produce no net force. Calculate the minimum speed of the electron.
A) 2.00*103 m/s
B) 4.00*103 m/s
C) 6.00*103 m/s
D) 8.00*103 m/s
E) 2.00*102 m/s
26. A wire carries a current of 10 A in a direction of 30° with respect to the direction of a
0.30-T magnetic field. Find the magnitude of the magnetic force on a 0.50-m length of
the wire.
A) 0.75 N
B) 1.5 N
C) 3.0 N
D) 6.0 N
E) zero
27. A circular loop of wire of radius 0.50 m is in a uniform magnetic field of 0.30 T. The
current in the loop is 2.0 A. What is the magnetic torque when the plane of the loop is
perpendicular to the magnetic field?
A) 0.73 m∙N
B) 0.52 m∙N
C) 0.47 m∙N
D) 0.41 m∙N
E) zero
28. What is the strength of a magnetic field 5.0 cm from a long straight wire carrying
4.0 A of current?
A) 3.8 × 10-6 T
B) 4.9 × 10-6 T
C) 1.6 × 10-5 T
D) 4.7 × 10-5 T
E) 5.1 × 10-5 T
Page 3 of 8
Physics 112
Exam 2
Summer 2006
29. Two long parallel wires carry currents of 5.0 A and 8.0 A in the opposite direction.
The wires are separated by 0.30 m. Find the magnetic force per unit length between the
two wires.
A) 2.7 × 10-5 N repulsive
B) 7.2 × 10-5 N repulsive
C) 2.7 × 10-5 N attractive
D) 7.2 × 10-5 N attractive
E) zero
30. A long solenoid has 100 turns/cm and carries current 1.00A. A sphere of the radius
1.00 cm is placed inside the solenoid. Find the magnetic flux through the sphere.
A) 1.6*10-6 T*m2
B) 1.6*10-7 T*m2
C) 4.0*10-8 T*m2
D) 8.0*10-8 T*m2
E) zero
31. What is the direction of the induced current in the circular loop due to the increasing
current shown below?
I increasing
A) counterclockwise
B) clockwise
C) the direction of the current is periodically changing
D) induced current is equal to zero
E) there is not enough information to answer the quastion
32. An AC generator consists of 100 turns of wire of area 0.090 m2 and total resistance
12 Ω. The loops rotate in a magnetic field of 0.50 T at a constant angular speed of 60
revolutions per second. Find the maximum induced emf.
A) 0.27 kV
B) 0.54 kV
C) 1.7 kV
D) 3.4 kV
E) 5.1 kV
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Physics 112
Exam 2
Summer 2006
33. Doubling the number of loops of wire in a coil produces what kind of change on the
induced emf, assuming all other factors remain constant?
A) The induced emf is 4 times as much.
B) The induced emf is twice times as much.
C) The induced emf is half as much.
D) The induced emf is 4 times less.
E) There is no change in the induced emf.
34. A simple RL circuit contains a 6.0-Ω resistor and an 18-H inductor. What is this
circuit's time constant?
A) 108 s
B) 3.0 s
C) 0.33 s
D) 0.20 s
E) 0.11 s
35. A 4.0-mH coil carries a current of 5.0 A. How much energy is stored in the coil's
magnetic field?
A) 80 mJ
B) 60 mJ
C) 50 mJ
D) 40 m J
E) 30 mJ
36. The magnetic field inside an air-filled solenoid 36 cm long and 2.0 cm in diameter is
0.80 T. Approximately how much energy is stored in this field?
A) 5 J
B) 11 J
C) 18 J
D) 21 J
E) 29 J
Page 5 of 8
Physics 112
Exam 2
Summer 2006
37. What is the current through a 2.50-mH coil due to a 110-V, 60.0 Hz source?
A) 0.94 A
B) 2.5 A
C) 104 A
D) 117 A
E) 154 A
38. A circular parallel-plate capacitor with plates 4.0cm in diameter is accumulating
charge at the rate of 3.0 mC/s at some instant of time. What is the magnitude of the
induced magnetic field at the distance 1.0 cm measured radially outward from the center
of the plates?
A) 2.0 T
B) 0.5 T
C) 2.0  10 8 T
D) 1.5  10 8 T
E) 0.5  10 8 T
39. An electromagnetic wave in vacuum is moving in +y direction. At time t=0 and at
position (x,y,z)=(0,0,0), the electric field is pointing in the +z direction. In what direction
is pointing the magnetic field at that time and position?
A) +x
B) –x
C) +y
D) –y
E) +z
40. If the magnetic field in a traveling EM wave has a peak magnitude of 17.5 nT at a
given point, what is the peak magnitude of the electric field?
A) zero
B) 1.75 V/m
C) 3.50 V/m
D) 5.25 V/m
E) 7.00 V/m
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Physics 112
Exam 2
Summer 2006
Scratch Paper (intentionally left blank)
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Physics 112
Exam 2
Summer 2006
Record Sheet
You may fill in this sheet with your choices, detach it and take it with you after the exam
for comparison with the posted answers
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