Microscopy Study

An Isotropic indicatrix is graphically represented by an?

Sphere

A positive Uniaxial Indicatrix is graphically represented by a

Prolate (elongated) spheroid

A Negative Uniaxial Indicatrix is graphically represented by a

Oblate (Flattened) spheroid

The type of polarizing light microscope viewing, that utilizes an Amici-Betrand lens and observes the back focal plane of the objective, is called?

Conoscopic viewing

Any Material which shows polarization colors between crossed polars, and in certain orientations, can be shown to have more than one principal refractive index, is called?

Anisotropic

Substances, which have no polarizing effects on the light and therefore remain dark between crossed polars, are called?

Isotropic

A material which exhibits a change in intensity or hue when its orientation to plane polarized light changes, is called?

Pleochroic

The difference in path length, equal to the thickness, times the birefrengence of material is known as….?

Retardation

A Contrast technique in which the phase position of the non-diffracted light is shifted in relation to the diffracted wave fronts, thereby improving the constructive and destructive interference conditions, is known as?

Phase Contrast Microscopy

The Principle of this contrast technique is similar to the principle of oblique illumination, and is distinct shadowing effect helps enhance specimen features…

Hoffman Modulation Contrast

A contrast technique in which a beam splitter shears or splits the incident light into two coherent components, one of which passes though the sample, and then a beam combiner recombines the two beams, is called?

Differential Interference Contrast

This contrast technique utilizes a central stop and an annual stop to produce “colors”, which can be used to help identify the specimen?

Dispersion Staining

Wayne Williams was a defendant in a multiple homicide case in which the FBI’s crime laboratory utilized this type of circumstantial evidence to convict the defendant for two of the murder charges?

Fiber Evidence

This Natural fiber exhibits incomplete extinction due to its spiral structure?

Cotton

If an anisotropic material, placed between crossed polars, goes to extinction, while parallel to the crosshairs, during rotation of the microscope stage, it exhibits what type of extinction?

Parallel Extinction

Calcite exhibits two principal refractive indices, “w” or “o” ray= 1.658, “c” or the “e” ray= 1.566. Therefore, calcite is a uniaxial material whose “w” ray is the slow ray, that is c < w, and by convention, has a _______ optic sign?

Negative

The following crystal systems are uniaxial anisotropic materials…

Tetragonal, Hexagonal, Rhombohedral

The following is the correct of terminology for cordage moving from the outside in toward the center…

Plies, Strands, Yarns, Fibers, Core

In a Twill Weave, each warp or filling yarn floats across two or more filling or warp yarns with a progression of interlacings by one to the right or left, forming a distinct diagonal line. This diagonal line is also known as a “whale”, true or false?

True

In which of the following types of forensic analyses is Phase Contrast Microscopy (PCM) typically utilized?

Sperm cell identification in sexual assault cases, and refractive index measurements in glass comparisons….. Both “a” and “c” are correct

Assuming that the “E” and “O” rays emerging above a uniaxial crystal do not interact but instead vibrate as separate entities, all of the following are true, Except….

All of the above

Looking down the acute bisectrix (Bx) in a biaxial interference figure, parallel to the ZY plane or the optic normal (that is, perpendicular to the Axial Plane (OAP)

B

The following is/are true about the crystal morphology, Except…

All of the above are true about crystal morphology

The true optic axial angle in a biaxial crystal is known as?

2V

Cotton is an example of a…

Seed hair

Marijuana can be identified “legally” in many jurisdictions by performing a color test for THC and microscopically identifying the following botanical structures…

Cystolith hairs, Glandular hairs, Conical trichomes…. “a”, “b”, and “c” are all botanical structures found in marijuana

The following optical test can be performed to determine whether a natural fiber exhibits an “s” twist or a “z” twist?

The Modified Herzog test

Linen or Flax is a example of a …

bast or stem fiber

The following natural fiber is long, smooth, luxurious, and may be confused with a synthetic fiber?

Silk

The following class of natural fibers exhibits many fibrils and transverse dislocations?

Bast or stem fiber

The following class of natural fibers may exhibit a cuticle?

Animal fiber

The most common vegetable fibers are mainly composed of the natural polymer…

Cellulose

The “z” ray or the “slow” ray of most compensators vibrates in…

Quadrant 1 & 3

Certain substances exhibit identical optical properties in all directions (in relation to the vibrational direction of the transmitted light) and are therefore called optically isotropic, True or False?

True

Most substances exhibit different optical properties in different directions and are therefore called optically anisotropic, birefringent, or doubly refractive, True or False?

True

If you cross your microscopes polars (polarizer and analyzer) and your sample exhibits positions of lightness or colors, then darkness or extinction, as its orientation to the direction of vibration of the light passing through it changes (as you rotate the microscopes stage) your material is considered Anisotropic, True or False?

True

An experienced microscopist can estimate the RI difference of a particle by observing the degree of contrast observed between the particle and its mounting medium, this is called?

Relief

Under axial illumination, a bright halo, the “Becke line”, will move toward the medium of lower RI when the focus is raised (that is, the working distance between the objective and the sample is increased), True or False?

False

In the “calcite Rhomb Experiment” that you performed in the laboratory, the following observations should have been made?

All of the above should have been observed

One of the easiest test to identify particles as starch grains is their appearance in polarizing light. With their high degree of internal organization and relatively round shape, starch grains are almost crystalline in structure and exhibit birefringence under cross-polarized light. True or False?

True

The picture below represents what type of device?

Spindle Stage

Why is it important to be able to measure the thickness of a synthetic fiber?

So that we can compare fibers of the same polymer type, and to help identify these fibers by their retardation colors….. Both a & b are correct

You need to be viewing down the optic axis (having the optic axial pane parallel to the light path) in order to view an interference figure in the back focal plane of the objective. What can be done to move the sample into this correct orientation?

Crystal rolling, use a spindle stage, use a goniometer stage…. “a” “b” and “c” will work

A filter that utilizes constructive and destructive interference to both restrict and allow certain wavelength of light (usually a narrow band of monochromatic light) to pass through it, is called?

an interference filter

Colorless cotton fibers are ubiquitous (found everywhere) and therefore are usually not very unique forensically, True or False?

True

Sodium Chloride Crystal (salt) exhibits what type of crystal system?

Cubic (or Isotropic)

The Particle in the picture belwo are probably?

Starch Grains

When observing the vibration direction of the resultant rays (at their points of emergence in a unaxial interference figure), all the rays emerging on or near the cross hair, will be extinguished by an N-S analyzer, and their point of emergence are thus marked by dark areas, True or False?

True

The above schematic best represents the proper way to measure the width of the following cross-sectional shaped fiber, when viewing it “longitudinally”, through a microscope?

Trilobal