PASCO OS-9257A PRECISION INTERFEROMETER - Manual (Page 25)

21
012-07137A Precision Interferometer
Experiment 2: The Index of Refraction of Air
Reference to – Procedure
1.
The chamber will be properly aligned when the reflec-
tions off the front and back end-plates are aligned with
each other and with the main interference pattern. (This
alignment may actually cause a secondary interference
pattern, but it will be very faint and will not affect your
measurements.)
2. It seems easiest to apply the vacuum first, then count
the fringes as the vacuum was released.
The average slope, starting at a guage reading of 60,
was 3.462x10 -6 .
0.9995
0.9996
0.9997
0.9998
0.9999
1
1.0001
1.0002
1.0003
1.0004
1.0005
0 10 20 30 40 50 60 70 80 90
Pressure (cm hg)
Answers to – Questions
1.
Extrapolating from our slope and the known index of
refraction of vacuum,
n
atm
= 1.000263.
2. Measure the index of refraction at various pressures,
and see if it increases linearly. (It does.)
3. Answers will vary; but they should include some way
of heating the air on one arm of the interferometer
without heating the air on the other arm or the inter-
ferometer itself.