ch. 5 forensics test; glass
phase
a uniform body of matter; different phases are separated by definite visible boundaries
which characteristic of glass does not belong; age, color, shape, chemical composition
age
plain glass has no regularity in the arrangement of its molecular constituent
amorphous
refractive index measures the speed of light in a vacuum to its speed in
any given substance
define matter
anything that has mass and occupies space
matter
anything that has mass and takes up space
in the immersion method of detecting glass refractive indexes you look for this
becke lines
this type of glass contains boron and has a trade mark named pyrex
borosilicate
how is the mass of an object determined
by comparing it against the known mass of standard objects
what property distinguishes different types of electromagnetic radiation from one another
by their frequency
if density of a solid is greater than the liquid medium in which it is immersed, the object will
sink
liquid glass is floated on molten tin, used in windows and cups and is very common is
soda-lime
what kind of glass is used commonly in bottles and windows
soda-lime glass
name the three states of matter
solid, liquid and gas.
safety glass, breaks into small squares, heated and cooled over and over it
tempered
what is the smallest particle of an element that can exist and still retain its identity
the atom
atom
the basic unit of a chemical element; not divisible by ordinary chemical means
a bright halo that is observed near the border of a particle immersed in a liquid of a different refractive index is known as
the becke line
refraction
the bending of a wave as it passes at an angle from one medium to another
what is refraction
the bending of light waves because of change in velocity
what is a phase
a uniform body of matter distinguished from other matter by definite visible boundaries
becke line
a bright halo that is observed near the border of a particle immersed in a liquid of a different refractive index
what is sublimation
a change of state from a solid to a gas
periodic table
a chart of the elements arranged in a systematic fashion. elements in a given group have similar properties
physical state
a condition or stage in the form of matter; solid, liquid or gas
radial fracture
a crack in a glass that extends outward like the spoke of a wheel form the point at which the glass was struck
concentric fracture
a crack in a glass that forms a rough circle around the point of impact
birefringence
a difference in the two indices of refraction exhibited by most crystalline materials
element
a fundamental particle of matter that cannot be broken down into simpler substances by chemical means
define element
a fundamental particle of matter that cannot be broken into simpler substances by chemical means
temperature
a measure of heat intensity, or the amount of heat in a substance
mass
a measure of how much matter is in an object
what is flotation
a method for measuring the density of glass
what is the smallest unit of a compound
a molecule
sublimation
a physical change from the solid state directly into the gaseous state; ex. dry ice sublimes into carbon dioxide gas
what is the difference between a physical property and a chemical property
a physical property describes a substance without reference to any other substance. A chemical property describes the behavior of a substance when it reacts or combines with another substance
density
a physical property of matter that is equivalent to the mass per unit of volume of a substance
weight
a property of matter that depends on both the mass of a substance and the effects of gravity on that mass
intensive property
a property that is NOT dependent on the size on an object
what is a compound
a pure substance composed of two or more elements
compound
a pure substance made of two or more elements chemically combined
physical property
a quality or condition of a substance that can be observed or measured without changing the substance's composition
photon
a small packet of electromagnetic radiation energy. each one contains a unit of energy equal to the product of Planck's constant and the frequency of radiation: E = hv, where E is energy in Joules, h is Planck's constant and v is the greek letter, nu, for frequency
crystalline solid
a solid that is made up of crystals in which particles are arranged in a regular, repeating pattern
how does flotation work
a standard/reference glass particle is immersed in a liquid whose composition is carefully adjusted until the object remains suspended in the liquid, glass chips of approximately the same size and shape are added to the liquid for comparison. If both the unknown and the standard/reference particles remain suspended in the liquid, their densities are equal to each other and to that of the liquid. Particles of different densities will either sink or float, depending on whether they are more or less dense than the liquid
liquid
a state of matter in which molecules are in contact with one another, but are not rigidly held in place
gas (vapor)
a state of matter in which the attractive forces between molecules are small enough to permit them to move with complete freedom
solid
a state of matter in which the molecules are held closely together in a rigid state
how is color related to the behavior of light
color is a visual indication of the fact that objects absorb certain portions of visible light and transmit or reflect others
what is laminated glass
created by sanwhiching one layer of plastic between two pieces of ordinary window glass
what physical properties are used most often to characterize glass particles
density and refractive index
amorphous solid
describes a solid that lacks an ordered internal structure; denotes a random arrangement of atoms
chemical property
describes the behavior of a substance when it reacts or combines with another substance
how is dispersion related to wavelength and frequency
each color corresponds to a different range of frequencies or wavelengths of light, light rays of one color bend to a different degree than rays of all other colors
visible light
electromagnetic radiation that can be seem with the unaided eye; detected as colored light ranging from red to violet in the electromagnetic spectrum
how are elements and matter related
elements provide the building blocks from which all matter is composed
what are the two most common temperature scales
fahrenheit and celsius
true or false: a significant difference in either density or refractive index proves that the glasses examined have a common origin
false
this laboratory method for identifying glass attempts to determine the density of the glass
floatation method
how did soda-lime glass acquire its name
from the fact that soda and lime are added to the glass to make it easier to work and to prevent it from dissolving in water
what is tempered glass
glass made stronger by introducing stress through rapid heating and cooling of the glass surfaces
tempered glass
glass that is strengthened by introducing stress through rapid heating and cooling of the glass surfaces
x-ray
high-energy, short wavelength form of electromagnetic radiation that can penetrate most solid matter and present the image on photographic film
if you find a piece of glass that fits exactly into the source, it is ______ type of evidence
individual
the composition of basic glass does not include
iron
what happens when tempered glass breaks
it does not shatter, but rather fragments or "dices" into small squares with little splintering.
regular glass is called soda-lime glass but also float glass because
it is floated on molten tin
tempered glass is strong and is also called safety glass because
it shatters into small non-sharp pieces
this type of glass is used for car windshields
laminate
how does weight differ from mass
mass is a constant property of matter that reflects the amount of material present, the mass of an object remains the same everywhere, while weight can vary depending on the force of gravity at a particular location
what is the formula for calculating the density of an object
mass per unit volume (M x V)
what is an example of a two-phase system
oil floating on water
which of the following is NOT a physical state of matter
plasma
glass ID method - uses glass immersed in liquids with known refractive indices
refractive/immersion method
what is the main ingredient in ordinary glass
sand
wavelength
the distance between crests of adjacent waves
wavelength is
the distance between crests of adjacent waves
electromagnetic spectrum
the entire range of radiation energy from the most energetic cosmic rays to the least energetic radio waves
three devices used for comparing the masses different objects
the equal-arm balance, the top-loading balance, the single-pan analytical balance
what is weight
the force with which gravity attracts a body
frequency
the number of complete waves that pass a given point in a certain amount of time
define dispersion
the process of separating light into component colors
refractive index
the ration of the speed of light in a vacuum to its speed in a given substance
dispersion
the separation of light into its component wavelengths
what chemical property determines its state
the strength of the attractive forces between its molecules
celsius scale
the temperature scale on which water freezes at 0 degrees and boils at 100 degrees, with 100 equal divisions or degrees between
farenheit scale
the temperature scale on which water freezes at 32 degrees and boils at 212 degrees, with 180 equal divisions or degrees between
what is the main drawback of using these properties to characterize glass (density and refractive index)
they are class characteristics and individualizing glass to a common source
how do forensic scientists use the knowledge of light behavior
they have learned to characterize different chemical substances by the type of quantity of light they absorb
how does a forensic scientist determine the refractive indices of suspect glass fragments
they use a process called immersion, in which glass particles are immersed in a liquid medium whose refractive index is adjusted by varying its temperature until it equals that of the glass particles. At this point, known as the match point, the observer notes the glass will seem to disappear from view or will be at minimum contrast with the liquid it is immersed in. also, the observer will note the disappearance of the becke line at the match point
what is the only way to individualize glass fragments found at a crime scene to a single source
to assemble the fragment and physically fit them together like a jigsaw puzzle
true or false: a high-velocity projectile, such as a bullet, will often leave a round, crater-shaped that is surrounded by a nearly symmetrical pattern of radial and concentric cracks
true
true or false: the "3R rule" states that "radial cracks form a right angle on the reverse side of the force"
true
true or false: the physical properties of density and refractive index are used most successfully for characterizing glass particles
true
true or false: visible light is only a small part of a large family of radiation that lies outside the electromagnetic spectrum
true
laminated glass
two sheets of ordinary glass bonded together with a plastic film
what part of the car is tempered glass used in
used in side and rear windows
three common compounds
water, carbon dioxide and salt
how might a forensic scientists tell which two fractures on a piece of glass created earlier
when there have been successive penetrations of glass, it is frequently possible to determine the sequence of impact by observing the existing fracture line and their points of termination. a fracture always terminates at an existing line of fracture
what part of the car is laminated glassed used in
windshields