Physics 112
Exam 3
Spring 2006
Name_________________
Physics 112
Spring 2006
Exam 3
Wednesday, April 12
Directions:
This 50-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 the 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.
Be sure to write you name on every sheet.
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 9
Physics 112
Exam 3
Spring 2006
41. Monochromatic light falls on two very narrow slits 0.048 mm apart. Successive
fringes on a screen 5.00 m away are 6.5 cm apart near the center of the pattern. What
is the wavelength of the light?
A.
B.
C.
D.
E.
620 nm
580 nm
540 nm
500 nm
460 nm
42. The separation of white light into colors by a prism is associated with:
A.
B.
C.
D.
E.
Total internal reflection
Partial reflection from each surface
Variation of index of refraction with wavelength
Polarization of light
Selective absorption of different colors
43. Radio waves are readily diffracted around buildings whereas light waves are
negligibly diffracted around buildings. This is because radio waves:
A.
B.
C.
D.
E.
Have much longer wavelengths than light waves
Have much shorter wavelengths then light waves
Are nearly monochromatic (single frequency)
Are amplitude modulated
Are plane polarized
44. In order to obtain a good single slit diffraction pattern, the slit width could be:
A. /100
B. /10
C. 
D. 10
E.100
45. Monochromatic light from a distant source is incident on a slit 0.75 mm wide. On a
screen 2.00 m away, the distance from the central maximum of the diffraction pattern
to the first minimum is measured to be 1.35 mm. Calculate the wavelength of the
light.
A.
B.
C.
D.
E.
253 nm
506 nm
555 nm
709 nm
1012 nm
Page 2 of 9
Physics 112
Exam 3
Spring 2006
46. White light, with uniform intensity across the visible range of 400 to 700 nm, is
perpendicularly incident on a water film, of index of refraction n=1.33 and thickness
t=320nm, that is suspended in air. At what wavelength is the light reflected by the
film brightest to an observer?
A.
B.
C.
D.
E.
245nm
450nm
482nm
512nm
567nm
47. Three polarizing sheets are placed in a stack with polarizing directions of the first and
third perpendicular to each other. What angle should the polarizing direction of the
middle sheet make with polarizing direction of the first sheet to obtain zero
transmitted intensity when unpolarized light is incident on the stack?
A.
B.
C.
D.
E.
0
30
45
60
All angles allow light to pass through
48. What is the focal length of the eye-lens system when viewing an object at 33 cm from
the eye? Assume that the lens-retina distance is 2.0 cm.
A.
B.
C.
D.
E.
0.5 cm
0.9 cm
1.5 cm
1.9 cm
2.5 cm
49. 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
Page 3 of 9
Physics 112
Exam 3
Spring 2006
50. What is the magnifying power of an astronomical telescope using a refracting mirror
whose radius of curvature is 6.0 m and an eyepiece whose focal length is 3.2 cm?
A.
B.
C.
D.
E.
-25x
-46x
-94x
-124x
-154x
51. Estimate the peak wavelength for radiation from the universe at 2.725 K, assuming
black-body radiation?
A.
B.
C.
D.
E.
2.16x10-15 m
3.02x10-14 m
2.56x10-8 m
4.18x10-5 m
1.06x10-3 m
52. The work function for a certain sample is 2.3 eV. What is the stopping potential for
electrons ejected from the sample by 7.0x1014 Hz electromagnetic radiation?
A.
B.
C.
D.
E.
0.1 V
0.6 V
0.9 V
1.5 V
9.0 V
53. Find the wavelength of the photon emitted by the hydrogen atom in the transition
from the first exited level of to the ground level.
A.
B.
C.
D.
E.
1450 nm
985 nm
550 nm
364 nm
122 nm
Page 4 of 9
Physics 112
Exam 3
Spring 2006
54. Franck and Hertz studied the motion of electrons through mercury vapor under the
action of an electric field. When the electron kinetic energy was 4.9eV or grater, the
vapor emitted ultraviolet light. What was the wave length of this light?
A.
B.
C.
D.
E.
150 nm
200 nm
250 nm
300 nm
350 nm
55. Which of the following electromagnetic radiations has photons with greatest energy?
A.
B.
C.
D.
E.
Blue light
Yellow light
X-rays
Radio waves
Microvaves
56. Determine the wavelength of an electron that has been accelerated through a potential
difference of 100 V.
A.
B.
C.
D.
E.
0.96 nm
0.48 nm
0.24 nm
0.12 nm
0.06 nm
57. What is the uncertainty in position, imposed by the uncertainty principle, on 150–g
baseball thrown at (93 ± 2) mph = (42 ± 1) m/s?
A.
B.
C.
D.
E.
1x10-3 m
2x10-6 m
3x10-14 m
4x10-24 m
7x10-34 m
Page 5 of 9
Physics 112
Exam 3
Spring 2006
58. An electron remains in an excited state of an atom for typically 10-8 s. What is the
minimum uncertainty in the energy of the state?
A.
B.
C.
D.
E.
0.7x10-7 eV
0.6x10-6 eV
0.5x10-5 eV
0.4x10-4 eV
0.3x10-3 eV
59. What is the energy difference between the first excited state and the ground state of
an electron in the “box” of size L=1nm?
A.
B.
C.
D.
E.
9.8 eV
6.3 e620 nm
2.5 eV
1.1 eV
0.5 eV
60. For n = 4, what values can l have?
A.
B.
C.
D.
E.
0, 1, 2
0, 1, 2, 3
0, 1, 2, 3, 4
-2, -1, 0, 1, 2
-3, -2, -1, 0, 1, 2, 3
Page 6 of 9
Physics 112
Exam 3
Spring 2006
Scratch Paper (intentionally left blank).
Page 7 of 9
Physics 112
Exam 3
Spring 2006
Answer key
41
51
A 620 nm
E 1.06x10-3 m
42
C Variation of index of
refraction with
wavelength
43
52
B 0.6 V
53
A Have much longer
wavelengths than light
waves
44
E
D 10
C
45
55
B 506 nm
C
46
56
E
567nm
47
A
122 nm
54
250 nm
X-rays
D 0.12 nm
57
0
E 7x10-34 m
48
58
D 1.9 cm
A 0.7x10-7 eV
49
59
B 3.3x
D
50
60
C
-94x
1.1 eV
B 0, 1, 2, 3
Page 8 of 9
Physics 112
Exam 3
Spring 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
41
51
42
52
43
53
44
54
45
55
46
56
47
57
48
58
49
59
50
60
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