1. Chapter 4 Section 2, Part A Glass Analysis Pg. 96 - 100

2. Refraction the bending of a light wave as it passes from one medium to another which causes a change in velocity

3. Refractive index ratio of the velocity of light in a vacuum to that in any medium; expressed as the equation: Refractive index = velocity of light in a vacuum velocity of light in medium ex: refractive index of water is 1.333 meaning light travels 1.333 times faster in a vacuum than it does in water at 25 degrees Celsius

4. Refractive index Varies with temperature and the frequency of the wavelengths Testing of a substance must be performed under carefully controlled temperature and lighting conditions

5. Refractive Index cont. All refractive indices are determined at a standard wavelength of 589.3 nanometers the predominant wavelength of sodium light Commonly known as sodium D light A solid or liquid exhibit only one refractive index value for each frequency of light except crystalline solids which have two refractive indices = called double refraction

6. Vocabulary Crystalline solids have definite geometric forms due to the orderly arrangement of the atoms that make up that solid (ex. Sodium chloride) Amorphous solids have their atomic arrangement randomly throughout (ex. Glass)

7. Vocabulary Birefringence – the difference between two refractive indices exhibited by crystalline solids Dispersion – the separation of light into its component wavelengths

8. Glass hard, brittle, amorphous substance composed of silicon oxides and various metal oxides

9. Types of Glass a. soda-lime-silicate glass (Na, Ca, Mg, Al, O) used for flat glass, bottles, light bulbs b. borosilicate glass car headlights, pyrex, thermometers, lab glass c. Aluminosilicate thermal resistant and used in lab glassware, stove top cookware d. lead-alkali-silicate glass commonly known as lead crystal and used in decorative glassware and neon signs

10. Glass cont. Tempered glass – produced by heating and cooling of the glass surfaces so that it fragments rather than shatters used in side and rear car windows and in foreign made car windshields Laminated glass – the layering of plastic between two pieces of glass used in US car windshields

11. Glass cont. Glass evidence has its greatest value when it can be individualized such as piecing together fragments from a crime scene matching irregular pieces and striations on the surface Physical properties of density and refractive index are most useful for characterizing glass particles considered to be a class characteristic

12. In-Class Assignment/Homework