PH113 Physics III
Test IV
Spring 1996/97
Name _________________________
(Please print in UPPER CASE BLOCK letters)
Section (hour) __________________
No books or paper notes are allowed. A one page formula sheet is attached as the last page of this test. It may be
removed and need not be handed in. You may use your laptop and any resources residing on your hard drive. This
includes Maple and Working Model. No network connections are allowed. Any student with a physical
connection between the computer and the network outlet during the test will receive a zero on the test.
Show all your work. No credit will be given for answers appearing without supporting calculations. Partial credit
may be awarded based on clarity and completeness of solution.
1. A laser beam with wavelength 633 nm is incident normally on two identical, closely-spaced
slits. The resulting interference pattern falls on a screen 2.50 m in front of the slits. A
photograph of the pattern is shown below along with a millimeter scale.
(a) Calculate the distance between the slits.
(b) Calculate the width of each individual slit.
PH113 Physics III
Test IV
Spring 1996/97
Name _________________________
(Please print in UPPER CASE BLOCK letters)
2. The photos at the right show interference
patterns from five different pairs of double slits.
(Each pattern is pictured at three different exposures
(short, medium, and long), so that details in the
central maximum and details on the fainter “wings”
can both be observed.) In all of the photographs the
wavelength of light was 633 nm, and the film was
2.50 m from the double slit.
Circle the correct response in (a) and (b).
(a) In the sequence of five sets of photos, the width
of the slits used
(i) increases from top to bottom
(ii) decreases from top to bottom
(iii) is the same from all five pairs of slits
(b) In the sequence of five sets of photos, the
distance between slits
(i) increases from top to bottom
(ii) decreases from top to bottom
(iii) is the same from all five pairs of slits
Now consider a set of four diffraction patterns as shown below. Each pattern is formed by
shining a HeNe laser through a set of slits as done in class. For each pattern the distance between
the slits and the screen is identical. The dark marks in the figure represent the red “dots” seen in
the classroom demonstrations.
(c) For which of the patterns A through D are the
slits the greatest distance apart?
(d) For which pattern A through D is the number of
slits illuminated the greatest?
PH113 Physics III
Test IV
Spring 1996/97
Name _________________________
(Please print in UPPER CASE BLOCK letters)
3. At the right is a photograph of a soap film as
viewed in reflected green light of wavelength 555
nm. Gravity causes the soap film to gradually
increase in thickness from top to bottom. Assume
the index of refraction of the soap film is n = 1.40
(a) At the top of the film, no light is reflected. (The
film is present! It just doesn’t reflect light) Explain
why no light is reflected. Use a diagram to aid you
explanation. Say what you can about the thickness
of the soap film.
(b) Farther down where the film is thicker is a
horizontal band where once again no light is
reflected. Explain why this band occurs. Use a
diagram to aid your explanation. Calculate the
thickness of the film in this band.
PH113 Physics III
Test IV
Spring 1996/97
Page 4 of 4
Name _________________________
(Please print in UPPER CASE BLOCK letters)
4. Light of wavelength 555 nm is emitted from a point source located 100. m from a circular
aperture of diameter 2.00 mm. Behind the aperture is a lens of focal length 2.20 cm. In the focal
plane of the lens is a screen. The image on the screen of the distant point is blurred by diffraction.
(a) Calculate the diameter of the central bright spot of the pattern formed on the screen. (This
diameter is defined as twice the distance from the center of the pattern to the first zero in the
diffraction pattern.)
(b) If the diameter of the aperture is increased to 6.00 mm, what happens to the diameter of the
central diffraction bright spot? (A qualitative answer is all that is required.)