chem forensic comp chap 4 study

chemical changes

change in identity nature of reacting materials

physical change

change in appearance but not fundamental nature

extensive

directly proportional to system size (mass)

intensive

independent of system size; characterize the nature of the material; useful for identification

imprints, indentations, striations and other toolmarks

exemplars

transparent

comes from quartz

translucent

comes from sand

radial cracks

form on opposite side of impact; form first; grow laterally from the load point

concentric cracks

form on same side of impact; form second; grow laterally to connect two radial cracks

wider

the exit hole is \___ than the entrance hole

radial, right angles, reverse side

3R rule

frequency

the number of cycles per time past a particular point

3 x 10^8 m/s

value of the speed of light

towards

when a ray of lights is traveling from a rarer medium to a denser medium, the refracted ray bends \___ the normal

away

from water to air, light rays bend \____ from normal

nearly invisible

when glass & liquid have same refractive index, particle will be

becke line

halo around particle

red, green, blue

the three major colors

all colors are reflected

see white

all colors are absorbed

see black

would see a blue/green

red absorbed

diameter \> 2 mm

gravel

between .05 mm and 2 mm

sand

between .002 mm and .05 mm

silt

clay

questioned samples

from the suspect/ on or from a victim

local variability

the forensic value of soil depends on its

1,100

how many colors are known

dry

the soil must be \___ to analyze color

munsell charts

used to determine colors

refraction

the bending of light

refractive index

a ratio that compares the speed of light in a vacuum to the speed of light in the material

gram, meter, liter

the basic units of measurement for length, mass ,and volume in the metric system

temperature

a measure of a substance's heat intensity

180

there are \___ degress fahrenheit between the freezing and boiling points of water

100

there are \___ degress celsius between the freezing and boiling points of water

mass

the amount of matter an object contains determines its

float

if an object is immersed in a liquid of greater density, it is

crystalline

solids having an orderly arrangement of their constituent atoms are

amorphous

solids that have their atoms randomly arranged

birefrigence

the crystal calcite had two indices of refractiom. the difference between these two values is known as

dispersion

the process of separating light into its component colors or frequencies is known as

glass, sand, quartz

a hard, brittle, amorphous substance composed of mainly silicon oxides

density and refractive index

the two most useful physical properties of glass for forensic comparisons are

floatation

comparing the relative densities of glass fragments is readily accomplished by a method known as

minerals

naturally occurring crystals commonly found in souls