The change in the refractive index value for tempered

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- The change in the refractive index value for tempered glass upon annealing is significantly greater when compared to non-tempered glass and thus serves as a point of distinction Glass Fractures Glass bends in response to any force exerted on any one of its surfaces; when the limit of its elasticity is reached, the glass fractures. - Fractured window glass reveals information that can be related to the forced and direction of an impact; such knowledge may be useful for reconstructing events at a crime scene investigation Radial Fracture is a crack in a glass that extends outward like the spoke of a wheel from the point at which the glass was struck (radiating lines) Concentric fracture is a crack in a glass that forms a rough circle around the point of impact. (circular lines)
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The presence of gunpowder deposits on the shattered glass fragments points to damage caused by a firearm. - When it penetrates glass, a high velocity projectile such as a bullet often leaves a round, crater shaped hole surrounded by a nearly symmetrical pattern of radial and concentric cracks. - The hole is inevitably wider on the exit side, and hence examining it is an important step in determining the direction of impact. However, as the velocity of the penetrating projectile decreases, the irregularity of the shape of the hole and of its surrounding cracks increase, so that at some point the hole shape will not help determine the direction of impact - Determining the radial and concentric fracture lines will help determine the direction of impact When a force pushes on one side of a pane of glass, the elasticity of the glass permits it to bend in the direction of the force applied. - Once the elastic limit is exceeded, the glass begins to crack Stress marks are shaped like arches that are perpendicular to one glass surface and curved nearly parallel to the opposite surface. The importance of stress marks stems from the observation that the perpendicular edge always faces the surface on which the crack originated. - The stress marks on the edge of a radial crack near the point of impact - The perpendicular end is always found opposite the side from which the force of impact was applied - Concentric fracture, the perpendicular end always faces the surface on which the force originated 3R rule- Radial cracks form a right angle on the Reverse side of the force. It is frequently possible to determine the sequence of impact by observing the existing fracture lines and their points of termination. A fracture always terminates at an existing line of fracture. Collection and Preservation of Glass Evidence Collect all the glass found at the crime scene. The evidence may ultimately prove invaluable in placing a suspect vehicle at the accident scene by matching the fragments with glass remaining in the headlight or reflector shell of the suspect vehicle - Examining the headlight’s filaments ma reveal whether an automobile’s headlights were on or off before the impact Evidence collector must submit all glass evidence found in the possession of the suspect along with a sample of broken glass remaining glass at the
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  • Fall '19
  • Light, Wavelength, refractive index

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