FIVS 215 Final: OPTICS, LIGHT, & MICROSCOPY

1. What is the formula for Numerical Aperture (NA) involving the acceptance angle (AA)?

NA = n·sin(AA/2)

2. What color temperature are indoor tungsten light films balanced for?

3200–3400 K

3. What is the average color temperature of the daylight spectrum?

~5500 K

4. Define color temperature.

A description of the color of light emitted by a blackbody radiator at a given temperature

5. In a twisted nematic LCD, what is the orientation of the two linear polarizers?

Their transmission axes are perpendicular

6. What happens to liquid crystal molecules in a twisted nematic LCD when voltage is applied?

They align parallel to the electric field and lose their twist

7. How does applying voltage cause an LCD pixel to appear black?

Light is no longer rotated and is absorbed by the second polarizer

8. What two phenomena cause the color sequence in a primary rainbow?

Two refractions

9. What causes polarization of light in a rainbow?

Internal reflection near the Brewster angle

10. A primary rainbow is caused by two refractions and how many internal reflections?

One

11. A secondary rainbow is caused by two refractions and how many internal reflections?

Two

12. What is the approximate polarization percentage of a primary rainbow?

~96%

13. What is Haidinger’s brush?

A faint visual pattern allowing perception of polarized light

14. For linearly polarized light, what direction do the yellow branches of Haidinger’s brush point?

Perpendicular to the vibration plane

15. How can Haidinger’s brush distinguish circular from slanted linear polarization?

By tilting the head and observing whether the pattern rotates

16. When does constructive interference occur in polarized light microscopy?

When rays arrive in phase

17. When does destructive interference occur in polarized light microscopy?

When rays arrive completely out of phase

18. Under crossed polars, what happens if the path difference is 1λ?

Light is extinguished

19. Under crossed polars, what happens if the path difference is 0.5λ?

Light is fully transmitted

20. What retardations are extinguished under crossed polars?

1λ, 2λ, 3λ, etc.

21. What is the formula for retardation?

Retardation = Δn × t

22. Define birefringence.

The absolute difference between refractive indices ε and ω

23. When does additive retardation occur?

When slow rays vibrate in the same plane

24. When does subtractive retardation occur?

When slow rays vibrate in perpendicular planes

25. What is pleochroism?

Direction-dependent absorption of light

26. What is a ray velocity surface?

A 3D plot of light velocity versus direction

27. What is the ray velocity surface for isotropic substances?

A sphere

28. In a uniaxial interference figure, what are dark wedge-shaped areas called?

Isogyres

29. How do you determine a positive uniaxial optic sign using a full-wave plate?

Subtraction quadrants form a plus sign perpendicular to the plate vibration

30. How do you determine a negative uniaxial optic sign using a full-wave plate?

Subtraction quadrants form a minus sign parallel to the plate vibration

31. What is the formula for the optic sign of a uniaxial crystal?

ε − ω

32. How does a centered biaxial interference figure change during rotation?

It cycles from a cross to curved isogyres

33. What are the colored curved lines in a biaxial interference figure called?

Isochromes

34. What is the geometric form of the biaxial indicatrix?

A triaxial ellipsoid

35. What do the three semiaxes of a biaxial indicatrix represent?

α, β, γ refractive indices

36. How is a positive biaxial optic sign determined?

β is closer to α

37. How is a negative biaxial optic sign determined?

β is closer to γ

38. What is the sign of elongation for fibers?

Length-fast (negative) or length-slow (positive)

39. State the Locard Exchange Principle.

Every contact leaves a trace

40. List four systematic crime scene search methods.

Strip, spiral, grid, quadrant

41. What three tasks must be done once evidence is discovered?

Document, collect, establish chain of custody

42. What is the difference between active and passive documentation?

Active uses the scientific method; passive guesses importance

43. Why should biological evidence never be packaged in plastic?

Plastic promotes mold growth

44. How should wet biological evidence be handled before packaging?

Allowed to air dry completely

45. What container is recommended for accelerant evidence?

Clean metal paint can

46. What is the typical order of laboratory analysis?

Trace → fingerprints → biological → ballistics

47. Name three types of animal hair.

Vibrissa, bristle, wool

48. Name four types of human hair.

Primordial, lanugo, vellus, terminal

49. What human hair types are most commonly examined forensically?

Terminal scalp and pubic hair

50. What proportion of the hair shaft does the medulla occupy in humans?

~1/3

51. What are the three structural components of hair?

Cuticle, cortex, medulla

52. Which hair component is birefringent?

Cortex

53. What are cortical fusi?

Air spaces within the cortex

54. What gives hair its color?

Melanin, cortical fusi, and air bubbles

55. What is the anagen phase of hair growth?

Active growth phase (80–90%)

56. What is the catagen phase of hair growth?

Transitional phase (~2%)

57. What is the telogen phase of hair growth?

Resting phase (10–18%)

58. What is the average growth rate of scalp hair?

~1 cm per month

59. What is the average duration of the anagen phase?

~1000 days

60. What part of hair is richest in nuclear DNA?

Follicular tag

61. How is mitochondrial DNA inherited?

Maternally

62. What mtDNA regions are used in forensics?

HV1 and HV2

63. What are down feathers?

Undercoating feathers with many barbs

64. What distinguishes goose barbules from duck barbules?

Smaller nodes and longer distal ends

65. What feature characterizes chicken and turkey barbules?

Even swellings resembling bamboo

66. What is the Paint Database Query System (PDQS)?

Automotive and architectural paint database

67. What distinguishes gymnosperms from angiosperms?

Exposed vs encapsulated seeds

68. What is the function of heartwood?

Structural support

69. What are the four Cs of diamond grading?

Cut, color, clarity, carat

70. How many milligrams are in one carat?

200 mg

71. What does 24K gold indicate?

Pure gold

72. How is specific gravity calculated?

Dry weight divided by loss of weight in water

73. What is Aqua Regia composed of?

1 part nitric acid, 3 parts hydrochloric acid

74. What is orthoscopic observation?

Normal specimen viewing

75. What is conoscopic observation?

Interference figure viewing at back focal plane

76. Which fibers typically show positive elongation?

Most fibers

77. Which fibers may show negative elongation?

Acrylics and some acetates

78. What are warp threads?

Lengthwise threads

79. What are weft threads?

Crosswise threads

80. Name three basic fabric weaves.

Plain, twill, satin

81. What is an adjudicative aid?

Evidence presented to assist the court

82. What is the difference between direct and circumstantial evidence?

Eyewitness vs inference

83. What is the purpose of Köhler illumination?

Even illumination without imaging the filament

84. Where is the lamp filament imaged in Köhler illumination?

Condenser aperture plane

85. Where is the field stop imaged in Köhler illumination?

Specimen plane

86. For a converging lens, where must an object be placed to form a real image?

Beyond the focal length

87. For a converging lens, where must an object be placed to form a virtual image?

Inside the focal length

88. What image does a microscope objective form?

A magnified real image

89. What image does the eyepiece form?

A magnified virtual image

90. What is the purpose of the field diaphragm?

Limit illuminated area

91. What is the purpose of the condenser aperture?

Control illumination cone

92. In the Becke line test, if the line moves into the particle, what does it indicate?

Particle has higher RI

93. In the Becke line test, if the line moves into the oil, what does it indicate?

Particle has lower RI

94. What is the 4R rule for glass fractures?

Radial ridges are at right angles to the rear

95. In ATR spectroscopy, what is the evanescent wave?

Surface-interacting wave