Exam 4
FISI-3172
Aug. 09, 2010
Dr. LU
(Write your answers on the answer sheets.)
1. A standard distance for the near point of a normal eye is (5 points)
a) 10 cm.
b) 15 cm.
c) 20 cm.
d) 25 cm.
2. If two light sources have waves leaving them that have the same wavelength,
same frequency, and bear the same phase relationship to each other, these are
called _________ sources. (5 points)
b) coherent
c) incoherent
d) phaseorded
a) full spectrum
3. A spectrometer is used to measure the _________ of light. (5 points)
a) intensity
b) wavelength c) phase
d) superposition
4. Imagine holding a circular disk in a beam of
monochromatic light. If diffraction occurs at the edge
of the disk, the center of the shadow is (5 points)
a) darker than the rest of the shadow. b) a bright spot.
5. An object is located 1.50 m from an 8.0-D lens. By how much does the image
move if the object is moved (a) 0.90 m closer to the lens, and (b) 0.90 m farther
from the lens? (20 points)
6. Light of wavelength 700 nm falls on two slits and produces an interference
pattern in which the third-order bright fringe is 40 mm from the central fringe on
a screen 2.5 m away. What is the separation of the two slits? (20 points)
7. Calculate the minimum thickness needed for an antireflective coating
 n  1.38
applied to a glass lens in order to eliminate (a) 470 nm, or (b) 710 nm reflections
for light at normal incidence. (20 points)
8. At what angle should the axes of two Polaroids be placed so as to reduce the
intensity of the incident unpolarized light to (a) 1/4 (b) 1/8? (20 points)
Bonus problem (20 points)
(a) Show that if two thin lenses of focal lengths f1 and f 2 are placed in contact
with each other, the focal length of the combination is given by fT  f1 f 2 /  f1  f 2  .
(b) Show that the power P of the combination of two lenses is the sum of their
separate powers, P  P1  P2 .