test: friday oct. 7 *properties of matter *density *properties of light *fracture patterns
TRANSCRIPT
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PROPERTIES OF LIGHT
FORENSIC LIGHT
Test: Friday Oct. 7*properties of matter
*density• *properties of light• *fracture patterns
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PROPERTIES OF LIGHT Light waves:
Differ in frequency and wavelengthspeed of light—299,792,458 m/s
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ELECTROMAGNETIC SPECTRUM
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PROPERTIES OF LIGHT 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
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PROPERTIES OF LIGHT Refraction:
The bending of light waves because of a change in velocity
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PROPERTIES OF LIGHT 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
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FORENSIC LIGHT AND GLASS Forensic scientists use two methods
when analyzing glass1. Determining the density of the shard of
glass in question2. Determining the refractive index of the
shard in question
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FORENSICS LIGHT AND GLASS 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
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BECKE LINES
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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.
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FORENSIC LIGHT SOURCES 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)
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FORENSIC LIGHT USES 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
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LATENT FINGERPRINTS
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BODILY FLUIDS Semen, saliva,
and vaginal fluidsall glow
Blood does not glow—it
appears black
Saliva
Semen
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DOCUMENTS--FORGERY
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.
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GUN SHOT RESIDUE
Under infrared light
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BONES
UV fluorescence of burnt bone
Bone fragmen
ts