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Physics 112
Exam 4
Summer 2012
Physics 112
Summer 2012
Exam 4
Thursday, August 2
Directions:
This exam consists of thirty two multiple-choice questions.
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.
When you are finished with the exam, return the bubble sheet and the exam itself.
Good luck!
Page 1 of 10
Physics 112
Exam 4
Summer 2012
61. Three identical charges of 3.0 μC are placed at the vertices of an equilateral triangle
which measures 30 cm on a side. What is the magnitude of the electrostatic force which
acts on any one of the charges?
A) 1.6 N
B) 1.8 N
C) 2.0 N
D) 2.2 N
E) 2.4 N
62. A solid block of metal is located in a uniform electric field, and is in electrostatic
equilibrium. What statement concerning the electric field in the block's interior is correct?
A) The interior field points in a direction opposite to the exterior field and is bigger.
B) The interior field points in a direction opposite to the exterior field and is smaller.
C) The interior field points in a direction that is parallel to the exterior field and is bigger.
D) The interior field points in a direction that is parallel to the exterior field & is smaller.
E) There is no electric field in the block's interior.
63. A uniform electric field, with a magnitude of 500 V/m, is directed parallel to the +x
axis. If the potential at x = 5.0 m is 2500 V, what is the potential at x = 2.0 m?
A) 500 V
B) 1000 V
C) 2000 V
D) 4000 V
E) 5000 V
64. A battery charges a parallel-plate capacitor fully and then is removed. The plates are
immediately pulled apart. (With the battery disconnected, the amount of charge on the
plates remains constant.) What happens to the potential difference between the plates as
they are being separated?
A) It increases.
B) It decreases.
C) It remains constant.
D) It is zero.
E) Cannot be determined from the information given
Page 2 of 10
Physics 112
Exam 4
Summer 2012
65. Consider two copper wires. One has twice the length and twice the cross-sectional
area of the other. How do the resistances of these two wires compare?
A) Both wires have the same resistance
B) The longer wire has twice the resistance of the shorter wire
C) The longer wire has four times the resistance of the shorter wire
D) The shorter wire has twice the resistance of the longer wire
E) The shorter wire has four times the resistance of the longer wire
66. Two resistors of 15 and 30 Ω are connected in parallel. If the combination is
connected in series with a 9.0-V battery and a 20-Ω resistor, what is the current through
the 15-Ω resistor?
A) 0.10 A
B) 0.13 A
C) 0.20 A
D) 0.26 A
E) 0.30 A
67. A 70-W, 110-V bulb is connected in parallel with a 40-W, 110-V bulb. What is the
net resistance?
A) 100 Ω
B) 110 Ω
С) 120 Ω
D) 130 Ω
E) 140 Ω
68. A 4.0-MΩ resistor is connected in series with a 0.50-μF capacitor. The capacitor is
initially uncharged. The RC combination is charged by a 9.0-V battery. What is the
change in voltage between t = RC and t = 3RC?
A) 11 V
B) 7.6 V
C) 5.7 V
D) 2.9 V
E) 1.3 V
Page 3 of 10
Physics 112
Exam 4
Summer 2012
69. The force on a current-carrying wire in a magnetic field is the strongest when
A) the current is parallel to the field lines
B) the current is at a 30° angle with respect to the field lines
C) the current is at a 45° angle with respect to the field lines
D) the current is at a 60° angle with respect to the field lines
E) the current is perpendicular to the field lines
70. Two long parallel wires carry currents of 20 A and 5.0 A in opposite directions. The
wires are separated by 0.20 m. At what point between the two wires are the contributions
to the magnetic field equal?
A) 0.040 m from the 20 A wire
B) 0.080 m from the 20 A wire
C) 0.12 m from the 20 A wire
D) 0.16 m from the 20 A wire
E) 0.18 m from the 20 A wire
71. An airplane with a wing span of 60 m flies horizontally at a location where the
downward component of the Earth's magnetic field is 6.0 × 10-5 T. Find the magnitude
of the induced emf between the tips of the wings when the speed of the plane is 225 m/s.
A) 0.41 V
B) 0.61 V
C) 0.81 V
D) 1.2 V
E) 1.4 V
72. A bar magnet falls through a loop of wire with the north pole entering first. As the
north pole enters the wire, the induced current will be (as viewed from above)
A) zero
B) clockwise
C) counterclockwise
D) to top of loop
E) a current whose direction cannot be determined from the information given
Page 4 of 10
Physics 112
Exam 4
Summer 2012
73. 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) 153 A
74. What is the frequency of 20 mm microwaves?
A) 100 MHz
B) 400 MHz
C) 15 GHz
D) 73 GHz
E) 98 GHz
75. Is it possible to see a virtual image?
A) No, since the rays that seem to emanate from a virtual image do not in fact emanate
from the image.
B) No, since virtual images do not really exist.
C) Yes, the rays that appear to emanate from a virtual image can be focused on the retina
just like those from an illuminated object.
D) Yes, since almost everything we see is virtual because most things do not themselves
give off light, but only reflect light coming from some other source.
E) Yes, but only indirectly in the sense that if the virtual image is formed on a sheet of
photographic film, one could later look at the picture formed.
76. A converging lens has a focal length f. An object is placed between f and 2f on the
axis. The image formed is located
A) at 2f
B) between f and 2f
C) at f
D) at a distance greater than 2f from the lens
E) at a distance smaller than f from the lens
Page 5 of 10
Physics 112
Exam 4
Summer 2012
77. In a Young's double slit experiment, if the separation between the two slits is 0.050
mm and the distance from the slits to a screen is 2.5 m, find the spacing between the firstorder and second-order bright fringes for light with wavelength of 600 nm.
A) 1.5 cm
B) 3.0 cm
C) 4.5 cm
D) 6.0 cm
E) 7.0 cm
78. A soap bubble has an index of refraction of 1.33. What minimum thickness of this
bubble will ensure maximum reflectance of normally incident 530 nm wavelength light?
A) 24.9 nm
B) 99.6 nm
C) 199 nm
D) 398 nm
E) 420 nm
79. Unpolarized light is passed through a polarizer-analyzer combination. The
transmission axes of the polarizer and the analyzer are at 30.0° to each other. What
percentage of the unpolarized light gets through the combination?
A) 37.5%
B) 50%
C) 75%
D) 84.5%
E) 100%
80. An important reason for using a very large diameter objective in an astronomical
telescope is
A) to increase the magnification.
B) to increase the resolution.
C) to form a virtual image, which is easier to look at.
D) to increase the width of the field of view.
E) to increase the depth of the field of view.
Page 6 of 10
Physics 112
Exam 4
Summer 2012
81. A farsighted person can read a newspaper held 25 cm from his eyes, if he wears
glasses of +3.33 diopters. What is this person's near point?
A) 4.2 cm
B) 25 cm
C) 31 cm
D) 1.0 m
E) 1.5 m
82. A person uses a converging lens of focal length 5.0 cm as a magnifying glass. What
is the maximum possible magnification?
A) 2
B) 3
C) 4
D) 5
E) 6
83. When light of wavelength 350 nm is incident on a metal surface, the stopping
potential of the photoelectrons is 0.500 V. What is the threshold frequency?
A) 3.47 × 1014 Hz
B) 3.74 × 1014 Hz
C) 4.73 × 1014 Hz
D) 7.36 × 1014 Hz
E) 9.21 × 1014 Hz
84. What is the energy difference between the second excited state and first excited state
of an electron in the “box” of size L=1nm?
A) 1.9 eV
B) 1.1 eV
C) 0.6 eV
D) 0.3 eV
E) 0.2 eV
Page 7 of 10
Physics 112
Exam 4
Summer 2012
85. In making a transition from state n = 1 to state n = 2, the hydrogen atom must
A) absorb a photon of energy 10.2 eV.
B) emit a photon of energy 10.2 eV.
C) absorb a photon of energy 13.6 eV.
D) emit a photon of energy 13.6 eV.
E) absorb a photon of energy 27.2 eV.
86. An electron has a wavelength of 0.123 nm. What is its energy in eV? (This energy is
not in the relativistic region.)
A) 20 eV
B) 60 eV
C) 80 eV
D) 100 eV
E) 120 eV
87. The probability of finding an electron in a hydrogen atom is directly proportional to
its
A) energy
B) momentum
C) angular momentum
D) wave function
E) square of the wave function
88. A neutral atom has an electron configuration of 1s22s22p6. If a neutral atom holds
one additional electron, what is the ground state configuration?
A) 1s22s22p63s1
B) 1s22s22p7
C) 1s22s32p6
D) 1s32s22p6
E) none of the given answers
Page 8 of 10
Physics 112
Exam 4
Summer 2012
89. The binding energy per nucleon
A) increases steadily as we go to heavier elements.
B) decreases steadily as we go to heavier elements.
C) is approximately constant throughout the periodic table, except for very light nuclei.
D) has a maximum near iron in the periodic table.
E) is a periodic function
90. Compared to the masses of its separate protons and neutrons, the total mass of a
stable nucleus is always
A) less
B) the same
C) greater
D) zero
E) could be less or grater
91. If the half-life of a material is 45 years, how much will be left after 100 years?
A) more than 1/2
B) less than 1/2 but more then 1/3
C) less than 1/3 but more than 1/4
D) less than 1/4
E) zero
92. What is the Q-value of the following reaction?
14N +
4He =
1p
17O
+
(14.003074)
(4.002603) (1.007825)
(16.999131)
A) 1.191 MeV
B) -1.191 MeV
C) 1.279 × 10-3 MeV
D) -1.279 × 10-3 MeV
E) zero
Page 9 of 10
Physics 112
Exam 4
Summer 2012
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
61
71
81
91
62
72
82
92
63
73
83
64
74
84
65
75
85
66
76
86
67
77
87
68
78
88
69
79
89
70
80
90
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