Microscopy Final Exam

What does 0 refer to in the following equation NA=n(sin0)

½ angle of cone of light

What is the refractive index

The light bending ability through a a particular medium

True or False: When light moves from a low RI to a high RI, the light moves faster and is not diffracted

False

What is numerical aperture?

The measurement of the lens's ability to allow/gather light and resolve minute details from a fixed objective distance, collecting as much diffracted light as possible, so we can see the fine details.

True or False: Depth of field is defined as the portion of the specimen that remains out of focus

False

Dispersion

Separation of light based upon wavelength

Absorption

How we see color, based on what wavelength is reflected off a surface

Interference

When two or more waves interact, resulting in an amplitude change

Refraction

When light passes through an object and the direction of light rays is changed

Positive lenses are

Convex, convergent

The location where the light rays converge

The focal point

How are smaller airy disks produced

High numerical aperture

True or False: Smaller Airy Disks have better resolving power

True

According to Abbe’s Theory of Imaging, for best resolution an objective must do what?

Collect the most possible light, maximize capture of light and collect multiple orders of diffraction

True or False: A real image is formed where light rays appear to have converge

False

If resolving distance r decreases, what happens to teh resolving power

The shortest distance between two points that allows for distinguishing as two discrete entities. The microscope’s ability top reveal fine details allows the resolving power to increase, and a smaller distance between two discernible points means we can see more detail

What are conjugate planes used for?

Used in Kohler Illumination to help properly align the microscope, points of convergence of light rays along a pathway, and lastly a set of planes in which a particular point is in focus each individual plane

(Conjugate Plane) Conoscopic Mode

1) Lamp/Lamp filament

2) Condenser/Aperture diaphragm

3) Objective Back Focal Plane

4)Eyepoint of Eyepiece

(Conjugate Plane) Orthoscopic/Normal Mode

1) Field Diaphragm

2) Object/Specimen Plane

3) Intermediate Image Plane

4) Retina

True or False: The condenser is important to microscopy and Kohler illumination because it produces grainless light that travels in perpendicular rays

False

How can Conjugate Planes be used to help trounleshoot issues with a microscope

This is particularly helpful in locating where potential contaminants are located in the microscope based on the conjugate plane it can be found in.

True or False: The two main categories of lens aberrations are chromatic and spherical

True

Which of the following can be used to help adjust an objective lens to account for varying cover glass thicknesses?

Correction Collar

What are isotropic materials?

The same optical properties (RI) in all directions, not dependent on orientation of light propagation

What are anisotropic materials

Different optical properties (RI) depending on the direction of light propagation

Why are anisotropic materials important for microscopy?

Anisotropic materials will exhibit birefringence. The difference in RI values can be measured and used to help determine the identity of an unknown substance

Achromat (Objective Lens Type)

Most common objective lens type

Fluroite (Objective Lens Type)

Manufactured with a different glass formulation

Apochromat (Objective Lens Type)

Highest level of correction

Plan (Objective Lens Type)

Corrections for curvature of field

What can a Michel-Levy chart be used to determine?

Birefringence, Retardation, Specimen Thickness

Birefringence

Optical property of a material that causes a single ray of light to refract into two rays upon passing through a material

Retardation

Phase shift when light rays split due to double refraction

Plane Polarized Light

The direction of the electric field oscillates in only one plane perpendicular to the direction of propagation

Unpolarized light

The direction of the electric field fluctuates randomly, oscillating in all directions

True or False: Birefringence is quantified by the maximum difference in measured RI in the sample

True

What are the components specifically needed for Polarized Light Microscopy?

Polarizer, Analyzer, and the Compensator Plate

Polarized light microscopy is utilized to determine what kinds of properties of the tested materials

Optical Properties

Polarizer (polarized light microscope components)

Filter placed between source of light and sample

Analyzer (polarized light microscope components)

Filter placed between the sample and the eyepiece

Compensator Plate (polarized light microscope components)

Component mounted between crossed polars to enhance phase difference and increase contrast

Rotating Stage (polarized light microscope components)

Allows rotation of the specimen

True or False: Anisotropic materials cannot exhibit Birefringence

False

How do we create polarized light?

Passing unpolarized light through a filter

Coma

Conical, comet-shaped blur

Astigmatism

Focal points vary across planes

Curvature of field

cannot focus center and periphery simultaneously

Distortion

Magnification of lens varies from center to periphery

True or False: Non-uniformity within a sample’s spatial distribution can lead to double refraction

True

What can a crossed-polars setup measure?

Degree of birefringence and the angle of extinction

What can a single polar set-up measure?

Refractive Index. dispersion and dichroism

How is a Michel-levy Chart used

It measures the birefringence via cross-polars, it plots retardation vs specimen thickness, and then compares the polarization interference colors to determine birefringence values of an unknown material that can be compared to known values

True or False: Syntetic fibers were the first manufactured fiber types

False

True or False: Delustrant particles are components added to synthetic fibers to make the resilient fiber less “shiny” and more opaque

True

What fiber types are considered regenerated?

Rayon and acetate

Melt Spinning

Forces the molten polymer through a spinnerette

Wet Spinning

Forces a polymer through a spinnerette which is then submerged in a bath

Filament Fibers

Fibers of a long, continuous length

Synthetic Fibers

Man-made fibers manufactured from entirely non-natural components

Staple Fibers

Fibers consisting of many shorter strands

Regenerated Fibers

Man-made fibers manufactured from a naturally occurring material

What is the most common type of natural fiber we see in forensics?

Cotton

What are the two major groups of fiber types?

Natural and man-made

How can the refractive index of a fiber be determined?

It can be determined by looking at the anisotropic material and the different refractive indices within the sample, both parallel and perpendicular.

1) Immersion Method: This is where the fiber is immersed in the refraction oils, where the fiber and the oil become one, and the contrast between the two lessens.

2) Becke Line: Where the fibers are immersed in a medium where a bright halo is formed close to the edge of the fibers or the particles. When we move our stage so that our objectives is further away from the fiber, we start to see a line move, this is the Becke line and it moves to the area of higher refractive index, this means the hair or fiber has a higher refractive index than the surrounding solutions.

Monoloid hair types typically have what type of cross-sectional shape

Round

What do public hairs often exhibit that can help us differentiate these hair types from other somatic origins

Buckling

A growth phase of hair that is characterized by a fully formed root bulb and is considered the resting stage?

Telogen

What growth phase tends to have a club-like shape?

Catagen

What scale structure do human hairs usually exhibit?

Imbracate

Difference between human hair and animal hair

1) Color: Human hair is constant, while animal hair varies and changes (banding)

2) Pigment distribution: Human is even and towards the cuticle, while animal is centered and towards the medulla

3) Medulla: Human have <1/3 width of shaft and it is amorphous and animal have >1/3 width of the shaft and is continuous

Primordial hair

hair grown during the 3rd month of gestation; coarse and whisker-like

Lanugo Hair

Fine, unpigmented hair typically shed after the 6th month of gestation, but may be found on newborns

Vellus Hair

Soft, short hair found across the body

Terminal Hair

Coarse, long hair found at specific site across the body

Which of the following would be a descriptive characteristic that could be used to describe a hair’s DISTAL END?

Frayed

When making a comparison, if either the questioned or known sample is sufficiently damaged or lacking enough information, the appropriate conclusionary statement would be what?

Unsuitable

Pili Annulati

Ringed hair, color banding of the hair shaft

Trichorrhexis Nodosa

Nodes along hair shaft, swelling of the hair shaft diameter

Pili Torti

Flattened and twisted hair shaft

Cartilage Hair Hypoplasia

Decreased hair diameter

What cannot be explained by normal accepted variances and should be taken into consideration when making comparisons>

Exclusionary differences

Why are acquired features of hair and hair shaft abnormalities important to observe and note?

Determine if there are any treatments or disease in our hair evidence and this is helpful to help individualized hair structure so we can make our comparisons

What is a stain that can be used to target nuclear material in hair roots

Hematoxylin

Where is the nucleus of the spermatozoa

It is in the head of the sperm

A hair without a root of sufficient tissue material is useful for what type of DNA analysis

Mitochondrial

Spermatozoa can be taken from a swab or the “male” fraction of what DNA Analysis extraction technique?

Differential Extraction

What is the red dye used for Christmas tree stains

Nuclear Fast Red

What is the green dye used for Christmas tree stains

Picoindigocarmine (PIC)

What are potential problems that must be taken into account when searching for potential spermatozoa in a sample?

Time since assult, oligospermia, aspermia

Approximately how many known head/scalp hairs should be collected from an individual?

50

What type of velocity impact fracture is characterized by a bulge on the opposite side from the impact?

A low velocity impact

Scrim

Loosely-woven guaze-type cloth added to duct tape for reinforcement and strength

Lay

The direction of strands in a helix about the rope or twine axis

Backing

A thin flexible material to which adhesive is applied

Twine

A strong thread consisting of two or more strands less than 4mm in diameter

What is not considered a common glass type found in forensics?

Tempered

What tape class does duct tape fall under

Polycoated Cloth Tape

What are the three main components of glass

1) Silicon dioxide

2) calcium and magnesium dioxide

3) Soidum Carbonate

Tape Lifts/ Vaccuming

Collecting loose trace evidence from a large surface area

Clipping

Recovering trace material from fingernails of a suspect or victim