Physics 224 - Exam #4 - Final
April 30, 2010
Name___________________________________________________
Total Problem 1:________________/25
Total Problem 2:________________/25
Total Problem 3:________________/25
Total Problem 4:________________/25
Total Problem 5:________________/25
Total Problem 6:________________/25
Total Problem 7:________________/25
Total Points:__________________________/ 150
Percentage Score:______________________
%
***You will answer ONLY 6 of the 7 problems for exam credit; your choice. All problems require you
to show all the steps in obtaining the answer and/or to provide clear and complete
descriptions/explanations. This includes, but is not limited to, defining all variables, showing the
equations to be used, explaining a concept and including units with all values listed. All problems are
worth up to 25 points each. Good Luck!!!!
1) A barrier is placed in front of, but not touching, a plane mirror. The barrier is perpendicular to the
mirror. Suppose you also have a laser. A target is placed successively at positions A, B, and C on
the left side of the barrier. NOTE: Two separate and complete setups are pictured (one for targets A
& B and a separate one for target C)!! Do not use any part of the lower setup to complete the upper
or vise-versa.
a. For target locations A and B, indicate a single location (if one exists) on the right side of the
barrier where the laser could be placed in order to hit the center of the target with the beam.
Be sure to explain how you determined these locations, the problem with finding a location (if
there was one), and illustrate your answers on the drawing.
b. For target location C, determine the entire region on the right side of the barrier in which the
laser could be placed in order to hit the center of the target with the beam; an indication that
there is more than one place you could place the laser and still hit the target. Be sure to
explain how you determined this region and illustrate your answer on the drawing.
2) In each of the two cases below, you are given two lines of sight to the image of an object in a plane
mirror. In addition, you are told where the object is located.
a. For each case, determine whether the situation is possible. If so, draw the location and
orientation of the mirror. Be sure to explain how you reached your conclusions.
3) The following are top view diagrams of a round glass block. Some of the diagrams represent
qualitatively correct paths for the laser beam through the block and some do not. Indicate which
diagrams have “flaws” and which ones do not. Briefly explain the flaw in the event you found one.
4) In order that you are to see a full-length view of yourself, the minimum vertical size for a plane
mirror (compared to your height) must be what? For a "full-length" view, consider that your eye must
be able to see the top of your head and also your feet. Construct the ray diagram to justify your
answer.
5) A laser beam strikes the left side (A) of a glass block at an angle of 20.0 o with respect to the
horizontal line indicated. The block has an index of refraction of 1.55 and is surrounded by air with an
index of refraction of 1.00. The left side of the block is vertical (90.0o from horizontal) while the right
side (B) is 60.0o from horizontal.
a) Trace the path of the ray through and out of the block.
b) Determine the angle with respect to horizontal at which the light exits surface B.
6) Two thin lenses are separated by 12 cm. The lens on the left has a focal length of -10 cm and the
one on the right has a focal length of +30 cm. An object is placed 15 cm to the left of the -10 cm focal
length lens.
a. Make a careful ray diagram and locate (approximately) the final image formed. HINT: The
image from the first lens becomes the object for the second!
b. Is it real or virtual? Upright or inverted? Enlarge or reduced?
7) A beam of light consisting of two wavelengths 6500 x 10-10 m and 5200 x 10-10 m is used to obtain
interference fringes in a Young's double slit experiment. The slit separation is 2 mm and the distance
from the slits to the screen is 120 cm. Assume a small angle approximation.
a. What is the distance from the central maximum to where the bright fringes due to both the
wavelengths first coincide (i.e. first overlap)?