Test: Friday Oct. 7
*properties of matter
*density
• *properties of light
• *fracture patterns
 Light
waves:
 Differ
in frequency and wavelength
 speed
of light—299,792,458 m/s
 Dispersion:



Process of separating light into its component
colors (ex: prism)
As visible light passes through the glass of a
prism each color composition of light is slowed to
a speed slightly different from the others.
Causes each component to bend at different
angles as it emerges from the prism
 Refraction:

The bending of light waves
because of a change in velocity
 Refractive



Index:
How much an object slows the speed of light
Ratio of velocity of light in a vacuum to its
velocity in any medium
RI = velocity of light in vacuum
velocity of light in medium
Varies with temperature of substance and
wavelength of light passing through it
 Forensic
scientists use two methods when
analyzing glass
1.
2.
Determining the density of the shard of glass in
question
Determining the refractive index of the shard
in question
 Refractive




Index of Glass:
A piece of glass in question is immersed in a
liquid medium whose refractive index is adjusted
until it equals that of the glass particles
At this point (match point), the observer notes
the disappearance of the Becke line
Becke line—halo near the border of glass particle
that is immersed in a liquid of different
refractive indices
The Becke line disappears when the medium
and fragment have similar indices
Each of these three identical jars contains a glass
stir rod. One jar is empty, and the entire rod is
visible. The second jar contains immersion oil,
which has the same refractive index as glass,
making the rod invisible. The third jar contains
water, and the rod appears bent.
 Forensic
light source is made up of a
powerful lamp containing UV, visible, and
infrared components of light
 3 techniques:



Fluorescence (evidence glows)
Absorption (evidence darkens)
Oblique lighting (small particles of
evidence revealed—hair, fibers)
 Detecting
latent fingerprints
 Detecting bodily fluids
 Hair and fibers
 Bruises, bite marks, pattern wounds
 Questioned documents—forgery
 Gun shot & explosive residue
 Bone fragments, tire tracks, shoe prints,
drugs

Blood

 Semen,
saliva, and
vaginal fluids

all glow
Semen
Saliva
does not glow—it
appears black
In works of art, modern
paint will fluoresce or
glow under a black light,
older paints will not.
Thus, pictures that have
been "touched up" with
modern paint will glow.
Bank notes also incorporate
fluorescent dyes, which glow
under exposure to UV
illumination. The color and
location of the security
thread in US dollar bills are
unique to the value of the
bill.
Under infrared light
UV fluorescence of burnt bone
Bone
fragments