Name: ___________________________
Refractive Index
Introduction:
The refraction of light is the bending of a light wave because of a change in
velocity when light passes from one medium to another. The refractive index can be
calculated by comparing the angles at which light travels through the two mediums. In
crime scene analysis, this information can be of value when attempting to determine the
origin of an unknown material.
Procedure: DO NOT SCRATCH MY GLASS SAMPLES!!!
ALWAYS PLACE THE GLASS ON A SHEET OF PAPER!!!
1. Set up the glass sample and laser on graph paper as shown in Fig 1.
Fig 1
2. Now draw a line along the surface of the glass sample as shown in Fig 2.
Fig 2
Name: ___________________________
3. Without moving the laser or the glass sample, place at least 2 dots on the laser
line going into the glass and 2 dots on the laser coming out of the glass as shown
in Fig 3.
Fig 3
4. Now you can remove the laser and the glass, they are no longer needed. Connect
the dots to the surface of the glass lines as shown in Fig 4. Draw the normal line
perpendicular to the glass surface on the side that the laser entered and at the
exact point that the laser entered the glass.
Fig 4
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5. If you connect the point of entrance of the laser to the point of exit, you are
retracing the path of the laser through the glass. Use a protractor to determine the
angle of incidence (Θi) and the angle of refraction (Θr).
Fig 5
6. Determine the refractive index using the following formula:
sin Θi
n = sin Θr
Record the refractive index in Table 1
7. Determine the refractive index for all samples provided in Table 1.
Name: ___________________________
Table 1
Sample
Calculated
Refractive Index
Actual
Refractive Index
3/8” Clear Glass
3/4” Acryllic
Questions
1. Summarize the phenomenon of refractive index in your own words.
2. Do all substances have the same refractive index?
3. What are the refractive indexes of the following materials:
Material
Beer
Diamond
Ice
Milk
Quartz
Ruby
Sapphire
Vegetable Oil
Water
Refractive Index
4. What is the only substance that has a refractive index of exactly1.0000? Why?
5. How can the determination of refractive index be used while processing a crime
scene?