PASCO TD-8565 Adiabatic Gas Law Apparatus - Manual (Page 7)

© 2009 Physics Enterprises 7
Target Students
High school and introductory college physics and chemistry.
Objectives
To observe that PV = const for constant temperature.
Physical Principles
When a process occurs with the system in contact with a heat reservoir to keep the
temperature fixed the process is considered “isothermal.” For such a process, the pressure is
inversely related to the volume, i.e.,
(2.1a)
Since Eq. (2.1a), Boyle’s Law, can be rewritten as
(2.2a)
one sees that a plot of ln(P) vs. ln(V) should be a straight line with a slope of –1.
const PV
=
( ) ( ) ( )
const V P
ln ln ln + − =
Procedure
Convert voltages to Pressure and Volume as in Experiment I using the Calculator in Data
Studio. Set up a graph of P vs. V.
Follow the procedure for the ideal gas law measurements (Experiment I) but slow the
Sample rate to one second and perform the compression slowly and steadily (quasi-
statically) over the course of a minute-or-so. This allows the temperature of the gas to always
remain at room temperature (isothermal). McNairy [1] recommends suspending a bucket
from the end of the handle and easing weights into the bucket. As you collect data, you can
watch the Pressure adjust to the slow change in Volume.
Experiment 2: Isothermal Processes
Experiment 2A: Boyle’s Law