A Level Physics Notes: Experimental Physics – Rotating Capillary Tube Experiment
Apparatus:
Capillary tube with mercury, ruler, plumb line, metre ruler and clamp stand.
Procedure:
1. Measure the length of the air column,
(in
mm) as a function of
from
=
0 to
=
180̊.
can
be found by measuring (with the aid of a metre rule and the
plumbline)
and
as defined in the diagram above (Do not use a protractor).
2. Measure the length of the mercury index, a (in mm) .
3. Draw a graph of
(in
)againstand
hence use it to find the atmospheric
pressure
(in
mm of mercury). (See below for theory).
4. Compare the value of atmospheric pressure found by using this method with the value measured using the Fortin barometer in the corridor.
Theory : From Boyle's Law
with
mm
of mercury
and
[
and
are
constants].
Boyle's law become
[
is
another constant]
therefore
and
so
leaving
Compare this with the equation of a straight line
Measure (or calculate) the gradient,
and
the
-
intercept,
And so find
where