You will have 50 minutes to complete this 100 point exam. Please use your time accordingly. Use the space beneath the question, or the back of the facing page to answer questions. Show your work where possible. For essay and short answer questions use concise but complete sentences and paragraphs, and good grammar. Use no notes or texts, and ask questions only of the proctor.
1) 20 pts. Describe the various experiments performed with hand-held polaroid filters and crystals, especially the calcite crystals. What were the major observations and the appropriate explanations?
2) 10 pts. How are colors produced in nature? Give examples from microscopy.
3) 10 pts. What is an optical indicatrix model and how is it used?
4) 10 pts. What is refraction? What is double refraction? How do they vary among various types of materials?
5) 5 pts. Draw and label the parts of a uniaxial interference figure for a crystal with the c-axis inclined 10 degrees to the NW. Draw the two vibration directions for a point in the SE sector.
6) 5 pts. A standard thin section is 0.03 mm thick. In such a section an unknown mineral displays retardation colors up to second order red. What is the birefringence of this mineral?
7) 5 pts. What is polarized light and what are some ways that it can form?
8) 5 pts. Sketch the indicatrix section for a uniaxial mineral and light transmission normal to the c-axis. Label the two vibration directions, the c-axis, and the optic axis.
9) 5 pts. What optical properties do isometric minerals have? What optical properties don’t they have that other mineral systems have?
10) 10 pts. Fill in blanks with best answer.
b) As above. What is the index of refraction? _________________
c) When focusing the microscope up above the specimen the Becke line moves _____________ the medium with the higher index of refraction.
d) A birefringence of ____________ would yield a maximum retardation of 600 nm in standard section (0.03 mm thick).
e) For apatite (a tetragonal mineral) oriented with the c-axis parallel to the stage, what type of interference figure would be seen? __________________
1. 425 nm
2. 625 nm
3. 425 mm
4. 625 mm
5. 5:25 pm
b) The quantitative expression of double refraction is:
1. Retardation
2. Birefraction
3. Direfraction
4. Birefringence
5. Direfringence
c) The magnifications available on typical student microscopes are:
1. 40, 100, 400
2. 40, 400, 1000
3. 4, 40, 400
4. 4, 100, 400
5. 10, 100, 1000
d) A retardation of 550 nm would yield an interference color of:
1. yellow (green)
2. green
3. gray
4. red (purple)
5. black
e) Working distance in microscopy refers to:
1. Distance between eye and ocular.
2. Distance between ocular and objective.
3. Distance between condenser and specimen.
5. Distance between microscope and seat.
13) 5 pts. True or false.
b) Hexagonal minerals should have isotropic optical properties.
c) Dispersion would account for the fiery colors seen in diamonds.
d) Pleochroism would account for the change in color of tourmaline when the microscope stage is rotated.
e) The ocular lenses are rotated in and out to change magnification.