Chapter 10 Matter, Light, and Glass Examination

Visible light

ranges in color from red to violet in the electromagnetic spectrum

Wavelength

the distance between two successive crests (or one trough to the next trough)

Frequency

the number of crests (or troughs) passing any one given point per unit of time

Frequency and wavelength

are inversely proportional to one another

The electromagnetic spectrum

the entire range of radiation energy from the most energetic cosmic rays to the least energetic radio waves

Glass

a hard, brittle substance that is composed of silicon oxides (sand) mixed with various metal oxides

Sodium carbonate (soda)

is normally added to sand to lower its melting point

Calcium carbonate (lime)

is normally added to the sand mix to prevent glass from dissolving in water

soda-lime

Forensic analysts usually examine “________” used to manufacture most window and bottle glass.

float

When molten glass is cooled on a bath of molten tin, it creates a type of glass called ________ glass, a type typically used for windows

Tempered glass

stronger than normal glass due to rapid heating and cooling of the glass surfaces

Laminated glass

found in car windshields has a layer of plastic between two pieces of ordinary window glass

Glass comparison

depends on the need to find and measure those properties that will associate one glass fragment with another while minimizing or eliminating other sources

Density and refractive index

To compare glass fragments, a forensic scientist evaluates two important physical properties:

The flotation method

a precise and rapid method for comparing glass densities

liquid

In the flotation method, a glass particle is immersed in a ________

density

The ________ of the liquid is carefully adjusted by the addition of small amounts of an appropriate liquid until the glass chip remains suspended in the liquid medium

remain suspended, sink, or float

Once the glass has the same density as the liquid medium, it can be compared to other relevant pieces of glass which will…

The immersion method

best used to determine a glass fragment’s refractive index

refraction

The bending of a light wave because of a change in its speed is called ________.

refractive index of that medium

The ratio of the velocity of light in a vacuum to its speed in any medium determines the…

The immersion method

involves immersing a glass particle in a liquid medium whose refractive index is varied until it is equal to that of the glass particle

The Becke line

a bright halo near the border of a particle that is immersed in a liquid of a different refractive index

The match point

when the Becke line disappears and minimum contrast between liquid and particle is observed

radiate outward (radial fractures) and encircle the hole (concentric fractures)

The penetration of window glass by a projectile, whether it is a bullet or a stone, produces cracks which…

the direction of impact

By analyzing the radial and concentric fracture patterns in glass, the forensic scientist can determine ________

Radial cracks

are formed first, commencing on the side of the glass opposite to the destructive force

Concentric cracks

occur afterward, starting on the same side as the force

A high-velocity projectile such as a bullet

often leaves a hole that is wider at the exit side

Radial cracks form a Right angle on the Reverse side of the force

The direction of impact can also be accomplished by applying the 3R Rule:

a new fracture always terminates at an existing line of fracture

The sequence of impacts when there have been successive penetrations of glass is frequently possible to determine because…

every effort must be made to collect all the glass found

If even the remotest possibility exists that glass fragments may be pieced together…

submit all glass evidence found in the possession of the suspect along with a representative sample of broken glass remaining at the crime scene

When an individual fit is thought improbable, the evidence collector must…

The glass fragments

should be packaged in solid containers to avoid further breakage

they should be individually wrapped in paper and transmitted to the laboratory

If the suspect’s shoes and/or clothing are to be examined for the presence of glass fragments…

Matter

Anything that has mass and occupies space is defined as ___________.

Elements

The basic building blocks of all substances are the ___________.

118

The number of elements known today is ___________.

Periodic

An arrangement of elements by similar chemical properties is accomplished in the ___________ table.

Atom

A(n) ___________ is the smallest particle of an element that can exist.

Compounds

Substances composed of two or more elements are called ___________.

Molecule

A(n) ___________ is the smallest unit of a compound formed by the union of two or more atoms.

Solid

The physical state that retains a definite shape and volume is a(n) ___________.

Has no

A gas ________ definite shape or volume.

Sublimation

During the process of ___________, solids go directly to the gaseous state, bypassing the liquid state.

Less

The attraction forces between the molecules of a liquid are ________ than those in a solid.

Phases

Different ___________ are separated by definite visible boundaries.

Density

Mass per unit volume defines the property of ___________.

Float

If an object is immersed in a liquid of greater density, it will ________.

Refraction

The bending of a light wave because of a change in velocity is called ___________.

Refractive index

The physical property of ___________ is determined by the ratio of the velocity of light in a vacuum to light’s velocity in a substance.

True

Solids having an orderly arrangement of their constituent atoms are crystalline.

Amorphous

Solids that have their atoms randomly arranged are said to be ___________.

Birefringence

The crystal calcite has two indices of refraction. The difference between these two values is known as ___________.

Dispersion

The process of separating light into its component colors or frequencies is known as ___________.

True

Color is a usual indication that substances selectively absorb light.

Wavelength

The distance between two successive identical points on a wave is known as ________.

False

Frequency and wavelength are directly proportional to one another.

electromagnetic

Light, X-rays, and radio waves are all members of the ___________ spectrum.

Lower

Red light is ________ in frequency than violet light.

Laser

A beam of light that has all of its waves pulsating in unison is called a(n) ___________.

Photons

One model of light depicts it as consisting of energy particles known as ___________.

True

The energy of a light particle (photon) is directly proportional to its frequency.

Less

Red light is ________ energetic than violet light.

Glass

A hard, brittle, amorphous substance composed mainly of silicon oxides is ___________.

Individual

Glass that can be physically pieced together has ___________ characteristics.

Density and refractive index

The two most useful physical properties of glass for forensic comparisons are ___________ and ___________.

False

Automobile headlights and heat-resistant glass, such as Pyrex, are manufactured with lime oxide added to the oxide mix.

Tempered glass

___________ glass fragments into small squares, or “dices,” with little splintering when broken.

Laminated

___________ glass gains added strength from a layer of plastic inserted between two pieces of ordinary window glass; it is used in automobile windshields.

Flotation

Comparing the relative densities of glass fragments is readily accomplished by a method known as ___________.

Becke line

When glass is immersed in a liquid of similar refractive index, its ___________ disappears and minimum contrast between the glass and liquid is observed.

Databases

The exact numerical density and refractive indices of glass can be correlated to ___________ in order to assess the evidential value of the comparison.

Radial fractures

The fracture lines radiating outward from a crack in glass are known as ___________ fractures.

Wider

A crater-shaped hole in glass is ________ on the side where the projectile entered the glass.

False

It is easy to determine from the size and shape of a hole in glass whether it was made by a bullet or some other projectile.

True

Stress marks on the edge of a radial crack are always perpendicular to the edge of the surface on which the impact force originated.

Will

A new fracture line ________ terminate at an existing line fracture.

Concentric fractures

Glass fracture lines that encircle the hole in the glass are known as ___________ fractures.

Opposite

When glass’s elastic limit is exceeded, the first fractures develop into radial lines on the surface of the ________ side to that of the penetrating force.

Rigid containers

Collected glass fragment evidence should be packaged in ___________ containers to avoid further breakage.

Paper

Glass-containing shoes and/or clothing should be individually wrapped in ___________ and transmitted to the laboratory.