Physics 109 - Index of Refraction
Today's lab begins with an Invention Activity
designed to get you ready for calculations that will be done in the
experiment below. Log on to http://tutor.phas.ubc.ca to begin the
activity. Once completed, you can move on to the experiment.
This experiment is an introduction to optics and will explore
Snell's Law, total internal reflection and Brewster's angle. The
experiment involves making precise optical measurements with a
laser and estimating the uncertainty in those measurements. These
measurments and the data analysis allow you to measure the index
of refraction n of
plexiglass in three different ways.
Check that the optical bench is aligned by setting the
incident angle in air to 0 degrees and observe
the position of the final spot. Rotate the plexiglass through 180
degrees so that the incident angle
through plexiglass is again 0 degrees. The position of the final
spot should not have moved.
If you feel that it is misaligned, contact your TA for help. DO NOT ADJUST ANY OF THE MIRRORS.
When entering the flat surface, the incident beam goes from air
(index of refraction ~1) to plexiglass (index of refraction is n).
By measuring the angle of the refracted beam and the angle of
incidence, the index of refraction can be determined from
n = Sin(incident
Use an incident angle of 60 degrees for this measurement.
Record your value of n determined by this measurement, including
an estimate of uncertainty.
ANGLE FOR TOTAL INTERNAL REFLECTION
With the beam entering the curved surface first,
search for the critical angle of incidence at which you judge total
internal reflection occurs. This is the incident
angle beyond which the beam is reflected, but with no refracted
beam. The index of refraction can be determined from this using:
Sin(critical angle) = 1/n
Record your value of n determined by this measurement,
including an estimate of uncertainty.
Brewster's angle is the angle of incidence at which the reflected
beam is completely polarized. With the beam entering the flat
surface first, determine the angle at which the reflected beam is
completely polarized. At this angle, a polarizer intercepting the
reflected beam can completely block it if it is oriented so that
only passes the opposite polarization. The index of refraction can
be determined from this using:
Tan(Brewter's angle) = n
Record your value of n determined by this measurment, including an
estimate of uncertainty.
Invention Activity: 2 marks
Hign quality measurment of index of refraction 3 different ways: 12
Don't forget to describe your procedures as you go along through the