PHY 102 Exam #3 Name ______

Problem / Points / Score
1 / 9
2 / 10
3 / 15
4 / 7
5 / 9

Total

/ 50

Instructions:

  1. Do all of your work in this booklet.
  2. Show all of your steps in problems for full credit.
  3. Be clear and neat in your work. Any illegible work, or scribbling in the margins, will not be graded.
  4. Place you answers in a box.
  5. If you need more space, you may use the back of the page and write On back in the problem space.

1. Multiple choice (9 pts) Find the answer which best fits the question and write it in the space provided.

a) Light travels fastest through

a) water. b) glass. c) air. d) benzene.

_____

b) The images of two sources are said to be resolved when what is
true of the diffraction patterns?

a) The central maxima fall on each other. b) The first bright
fringes fall on each other. c) The central maximum of one
pattern falls on the first dark fringe of the other one.
d) None of these.

_____

c) The separation of light into its component colors is called

a) refraction; b) dispersion; c) polarization; d) reflection.

_____

d) The lens of a farsighted eye focuses parallel rays to form an
image behind the retina. This can be corrected by

a) a converging lens; b) a diverging lens; c) more

intense light; d) none of these.

_____

e) While underwater, a diver sees a bird flying above the surface.
The image seen actually appears ______the diver than the
bird.

a) closer to; b) further from; c) the same distance from.

_____

f) If the object distance is less than the focal length of a concave
mirror, the image formed will be

a) inverted. b) larger than the object. c) real. d) none of these.

_____

g) For a diverging lens the image always appears

a) real, inverted, smaller; b) virtual, inverted, larger;

c) virtual, upright, smaller; d) real, upright, larger;

e) none of these.

_____

h) Which of the following is bent the least as it passes through a
diffraction grating?

a) red b) green c) blue d) violet.

_____

i) Polaroid sun glasses have an axis of polarization that is
a) horizontal b) vertical c) at 45o d) none of these.

_____

2. LakeProblems (10 pts) Assume that the index of refraction for water is 1.33. A flashlight is located 20 inches below the surface of a clear lake.

a) If the flashlight beam is aimed at 30o to the normal, at what angle does the beam emerge?

b) At what angle must the flashlight be aimed for total internal reflection?

c) How deep does the flashlight appear to a person looking into the lake from above?

d) What is the angle at which incident light reflected off the lake surface 100% polarized?

e) What is the speed of light in the water?

______

Bonus: Light passes from material A with an index of refraction 4/3 into material B with an index of refraction 5/4. Find the ratio of the speed of light in material B to that of material A.

3. Other Problems (15 pts)

a. Unpolarized light with intensity 1.0 W/m2 strikes a piece of polarizing material. It passes through and comes into contact with another polarizing material, which is at 30o with respect to the first. What is light intensity that is transmitted through these polarizing materials?

b. A child looks at a reflecting ball that has a diameter of 5.0 cm. She sees an image of her face that is a fifth the real size. How far is the child's face from the ball?

c. A farsighted person cannot see objects that are closer than 50 cm from the eye. Determine the focal length of the contact lenses that would enable the person to read a book at the normal near point.

d. With two slits spaced 0.20 mm apart and a screen at a distance of L = 1.0 m, the second bright fringe is found to be displaced 4.0 mm from the central fringe. Find the wavelength of the light.

e. A thin film of gasoline (n=1.40) floats on a piece of glass (n=1.50). What is the minimum thickness of the film if there is no blue light (450 nm) in the reflected light?

4. Optical System (7 pts) A converging lens has a focal length of 10 cm. An object, which is 4 cm high, is placed at a point 30 cm to the left of the lens.

a) What is the position and size of the image?

b) Now, place a concave spherical mirror 30 cm to the right of the lens. Assume that the radius of curvature of the mirror is 5 cm. What is the position and size of the new image?

c) What is the total magnification of this system?

5. Ray Diagrams (9 pts) Sketch the ray diagrams for the following systems. Clearly show the images and indicate if they are real/virtual, larger/smaller and upright/inverted.