Physics AP - Speed of Light in Glass (#25)

Background:
The index of refraction (n) is a constant that is equal to the
velocity of the speed of light through air (v0) divided by the
velocity of the speed of light through glass or any other substance
(vg).  This is proven also through Snell's Law, which states that the
sine of the angle of incidence (i) divided by the sine of the angle
of refraction (r) is equal to the index of refraction. The incident
ray goes into the glass at the angle of incidence, and gets
refracted, and causes the angle of refraction.  The light ray then
comes out of the other side of the glass parallel to the incident
ray.

Problem:
To find the index of fraction of that piece of glass, then from that
find the speed of light through that piece of glass.  Graph a best-
fit line of the sine of the angle of incidence, and the sine of the
angle of refraction.
 
Materials:
Rectangular piece of glass, protractor, ruler, paper and pencil.

Procedure:
1. Place the glass in the center on the paper and draw the outline of
   the block.
2. Then from the upper left-hand corner move a centimeter, and draw a
   perpendicular line, called the Normal.
3. With the protractor measure 10° to the left and draw a line, that
   angle will be the angle of incident for that number of degrees.
4. Repeat step number 3 until you get out two 70°.
5. Then using you're a ruler and you eye look through the glass and
   see where the light rays comes out the other side, and draw an
   line there, do this for every 10° marking.
6. After that draw a line connecting all the incident rays and
   emerging rays, that line is the refracted ray.
7. Now measure the angle or refraction, which is between the Normal
   and the refracted ray for all the lines.
8. Then calculate the sine of the angle of incidence, and the sine of
   the angle of refraction to find the index of refraction.
9. Once you have found that find the speed of light through the glass
   by using the equation vg=vo/n.

Data:
Angle of Incident (i)   0°      10°     20°     30°     40°     50o	60o	70°
Angle of Refraction (r) 0°      8°      14.5°   19°     26.5°   31o	36o	39°
Sin (i)                 0       .1736   .3420   .5000   .6428   .7660	.8660	.9397
Sin (r)                 0       .1392   .2504   .3256   .4462   .5150	.5878	.6293
Index of Refraction (n) 1.435   1.247   1.366   1.536   1.441   1.487	1.473	1.493

vg=vo/n, 3.00x108/1.435 ==> note: 8 is an exponent
vg=2.09x108(m/s)        ==> note: 8 is an exponent

Analysis/Conclusion:
The conclusion I made from this lab is the index of refraction is
pretty constant even when the lines of the emerging rays are off
some.  That is why the index of refraction is no perfectly constant
in this lab, if the emerging ray would have been better the index of
refraction would have been better also.