CJO3 EOC Review

2014-2015

Unit 11 – GlassO 25.07 – Describe broken glass

examination procedures

What are general properties of glass?

OHard solidOMade by melting sand and lime at

very high temperaturesOCan be polished, ground, or cut

once cooledOAmorphous material – Has an

irregular atomic structureOBreaks in a variety of fracture

patterns

What properties of glass allow for comparisons?

OChemical composition/properties

OShatter patternsOThicknessOColorODensityORefractive index

What is the formula for calculating density?

OD = m/VOD = Density (g/ml)Om = Mass (grams)OV = Volume (milliliters)

How is mass measured for purposes of calculating density?

OBy using a balance

How is volume measured for purposes of calculating density?

OBy placing the glass fragments into a beaker filled with water and measuring the overflow in a graduated cylinder

How is refractive index calculated?

OSnell’s LawOBecke Lines

What is the formula for Snell’s Law?

On1 (sine angle 1) = n2 (sine angle 2)On1 = 1 (refractive index of

air)OAngle 1 = Angle of incidenceOn2 = refractive index of glassOAngle 2 = Angle of refraction

What is a Becke Line and how is it interpreted?

OA halo-like effect appearing on the edge of a glass fragment when submerged in a liquid of differing refractive indexO Line inside the glass = Glass refractive

index is higher than the liquidO Line outside the glass = Glass

refractive index is lower than the liquid

What are radial fractures and how can they help determine direction of travel?

OImpact fracturesOAppear 1st

OFound on opposite side of force

OCreate straight lines that extend from the point of impact

What are concentric fractures and how can they help determine direction of

travel?

OImpact fracturesOAppear 2nd OFound on the same side as the force

OCreate circular lines around the point of impact

In reference to bullet holes, how else can direction of travel be determined?

OExamine the cone-shaped hole

OLarger side = ExitOSmaller side = EntryOAngle = Possible shooter position

How can bullet holes be sequenced?

OExamine the fracture lines

OA new fracture line will always stop when it reaches an existing one