Boyles law – pressure and volume of an ideal gas EXPERIMENTS
::
E-201
3) Now open the air release valve and adjust the piston
so that its front edge again flush with the middle sca-
le marking. Close the air release valve. Pull the piston
outwards until the volume of the trapped air is doub-
led. Observe that the pressure has fallen to 5 N/cm
2
.
4) Note the corresponding values of the volume and the
pressure. The constant K can now be computed.
According to Boyle’s law all the values of K should be the
same. Small deviations are acceptable.
The above procedure is appropriate to a classroom
demonstration. In the laboratory you may wish to take a
larger number of measurements (e.g. about 8 or 10) so
that there will be more data to work with.
Remarks
Purpose
The piston should not be pressed with so much force
The goal of this experiment is to illustrate the relation ship that the pressure exceeds 25 N/cm
2
, because the mano-
between the volume and pressure of an ideal gas at con- meter calibration may be altered. Excessive force will
stant temperature. ruin the instrument.
Theory
If the experiments are performed very rapidly, the effects
of temperature changes (temperature increase during
The behaviour of an ideal gas at constant temperature
compression, temperature drop during expansion) can
can be expressed as follows:
be observed. E.g. if the pressure is halved very quickly,
the air in the cylinder will be heated slightly (just as is
p
.
V = K
observed when you pump your bicycle tire). Before the
air cools the pressure may reach 22 N/cm
2
. But the air
where p is the pressure of the gas, V is it’s volume and K
quickly cools off so the assumption of constant tempe-
is a constant which remains the same for a given quan-
rature is fulfilled, and the pressure will drop to the Boy-
tity of gas at constant temperature. During the experi-
le’s law value of 20 N/cm
2
.
ment corresponding values of p and V will be noted, and
the constant K can be found.
Procedure
1) Open the air release valve. The air pressure can be
read on the scale (in this case 10 newtons per squa-
Requir
Requir
ed Equipment
ed Equipment
re centimeter).
1805.00
Itemno. Name
Boyle Mariotte Apparatus 1 pcs.
2) Adjust the front edge of the piston so that it is in line
with the middle scale marking. Now close the air re–
lease valve. Compress the trapped air using the
piston until the volume is halved. Note that the pres-
sure has increase to 20 N/cm
2
.
®
Science Equipment for Education Physics
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