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= 180 .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