Physics 112
Exam 3
Summer 2014
Name_________________
Physics 112
Summer 2014
Exam 3
Monday, July 28
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.
When you are finished with the exam, return the bubble sheet, the exam itself, and scratch paper
that you used for the exam.
Good luck!
Page 1 of 7
Physics 112
Exam 3
Summer 2014
41. How far are you from your image when you stand 0.75 m in front of a vertical plane mirror?
A) 0.75 m
B) 1.5 m
C) 3.0 m
D) 3.75m
E) 4.5m
42. The image formed by a plane mirror of a real object is always
A) Real, erect, and smaller than the object
B) Real, inverted, and the same size as the object
C) Real, erect, and the same size as the object
D) Virtual, inverted, and larger than the object
E) Virtual, erect and the same size as the object
43. The critical angle for a substance is measured at 53.7°. Light enters from air at an angle of
45.0° to the normal. At what angle will it continue?
A) 34.7°
B) 45.0°
C) 53.7°
D) 58.2°
E) It will not continue, but will be totally reflected.
44. A concave mirror with a radius of 20 cm creates a real image 30 cm from the mirror. What is
the object distance?
A) 30cm
B) 20 cm
C) 15 cm
D) 7.5 cm
E) 5.0 cm
Page 2 of 7
Physics 112
Exam 3
Summer 2014
45. When a person stands 40 cm in front of a cosmetic mirror (concave mirror), the erect image
is twice the size of the object. What is the focal length of the mirror?
A)
B)
C)
D)
E)
27 cm
40 cm
80 cm
100 cm
160 cm
46. An object is placed 40 cm in front of a 20 cm focal length converging lens. How far is the
image of this object from the lens?
A)
B)
C)
D)
E)
40 cm
30 cm
20 cm
13 cm
8 cm
47. Radio waves are diffracted by large objects such as buildings, whereas light is not noticeably
diffracted. Why is this?
A)
B)
C)
D)
E)
Radio waves are unpolarized, whereas light is plane polarized
Radio waves are polarized, whereas light is plane unpolarized
Radio waves are coherent and light is usually not coherent
The wavelength of light is much greater than the wavelength of radio waves
The wavelength of light is much smaller than the wavelength of radio waves
48. A beam of light (f = 5.0 × 1014 Hz) enters a piece of glass (n = 1.5). What is the frequency
of the light while it is in the glass?
A)
B)
C)
D)
E)
5.0 × 1014 Hz
7.5 × 1014 Hz
3.3 × 1014 Hz
1.0 × 1014 Hz
2.5 × 1014 Hz
Page 3 of 7
Physics 112
Exam 3
Summer 2014
49. 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 first-order and
second-order bright fringes for light with wavelength of 600 nm.
A)
B)
C)
D)
E)
1.5 cm
3.0 cm
4.5 cm
6.0 cm
7.5 cm
50. In a single slit diffraction experiment, if the width of the slit increases, what happens to the
width of the central maximum on a screen?
A)
B)
C)
D)
E)
It increases.
It decreases.
It remains the same.
It depends on the distance to the screen.
There is not enough information to determine.
51. In order to obtain a good single slit diffraction pattern, the slit width could be:
A)
B)
C)
D)
E)
/100
/10

10
100
52. Two stars that are 15 light-years away are barely resolved by a 55-cm (mirror diameter)
telescope. How far apart are the stars? Assume   550 nm and that the resolution is limited
by diffraction. (1 light-year = 9.46x1015 m)
A)
B)
C)
D)
E)
1.3x107 m
1.4x108 m
1.5x109 m
1.6x1010 m
1.7x1011 m
Page 4 of 7
Physics 112
Exam 3
Summer 2014
53. A diffraction grating has 5000 lines per cm. The angle between the central maximum and the
fourth order maximum is 60°. What is the wavelength of the light?
A)
B)
C)
D)
E)
138 nm
183 nm
367 nm
433 nm
637 nm
54. What is the minimum thickness of a nonreflecting film coating (n = 1.30) on a glass lens (n =
1.50) for wavelength 500 nm?
A)
B)
C)
D)
E)
250 nm
192 nm
167 nm
96.2 nm
57.3 nm
55. An ideal polarizer is placed in a beam of unpolarized light and the intensity of the transmitted
light is I. A second ideal polarizer is placed in the beam with its preferred direction rotated
40° to that of the first polarizer. What is the intensity of the beam after it has passed through
both polarizers?
A)
B)
C)
D)
E)
0.77I
0.64I
0.59I
0.41I
0.36I
56. A beam of unpolarized light in air strikes a flat piece of glass at an angle of 57.3°. If the
reflected beam is completely polarized, what is the index of refraction of the glass?
A)
B)
C)
D)
E)
1.50
1.52
1.54
1.56
1.58
Page 5 of 7
Physics 112
Exam 3
Summer 2014
57. A near-sighted person has a far point of 20 cm. What lens (in diopters) will allow this person
to see distant objects clearly? Assume that the lens is 2.0 cm from the eye (typical for
eyeglasses)
A)
B)
C)
D)
E)
+ 5.6 D
- 5.6 D
+ 0.056 D
- 0.056 D
-5.0 D
58. A magnifying glass with a focal length of 8.5 cm is used to read print placed at a distance 7.5
cm. Calculate the angular magnification.
A)
B)
C)
D)
E)
2.3x
3.3x
4.3x
5.3x
6.3x
59. A person is designing a 10X telescope. If the telescope is limited to a length of 20 cm, what
is the approximate focal length of the objective?
A)
B)
C)
D)
E)
16 cm
17 cm
18 cm
19 cm
20 cm
60. What power lens is needed to correct for farsightedness where the uncorrected near point is
75 cm?
A)
B)
C)
D)
E)
+ 2.7 D
- 2.7 D
+ 5.3 D
- 5.3 D
+6.0 D
Page 6 of 7
Physics 112
Exam 3
Summer 2014
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
41
51
42
52
43
53
44
54
45
55
46
56
47
57
48
58
49
59
50
60
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