scientific
9
012-02675B
Interferometer
method you find to be easier for controlling the air flow.)
Record P
i
, the initial reading on the vacuum pump gauge.
P
i
= ________________ cm Hg
➦
NOTE: P
i
and P
f
(see below) must be absolute pressure readings. Most vacuum gauges
measure vacuum pressure with respect to atmospheric pressure (e.g., when the gauge reads
34 cm Hg, it means that the pressure is actually 34 cm Hg BELOW atmospheric pressure).
In this case, the absolute pressure reading must be calculated as:
P
absolute
= 76 cm Hg - P
gauge
Of course, your room pressure may vary slightly from 76 cm Hg. If you have a more
accurate way of measuring room pressure, you can use that value to replace 76 cm Hg in
the above equation.
Mark a reference point between a pair of fringes on your viewing screen. Slowly pump out
the air in the vacuum chamber to some convenient pressure level. As you do this, count
∆
m, the number of fringes that pass your reference point. Record
∆
m, below. Also record
P
f
, the final reading on the vacuum gauge.
∆
m = ______________
LASER
VIEWING SCREEN
VACUUM CHAMBER
(front view)
INTERFEROMETER
BASE
BANANA PLUG
VACUUM RELEASE
TOGGLE SWITCH
VACUUM PUMP
MODEL OS-8502
AIR HOSE
VACUUM CHAMBER
Figure 9 EXPERIMENTAL SETUP
➃
➅
➆
P
f
= _______________ cm Hg.
