PASCO TD-8565 Adiabatic Gas Law Apparatus - Manual (Page 11)

© 2009 Physics Enterprises 11
Experiment 3: Adiabatic Processes
Experiment 3A: Adiabatic Gas Law
Objectives
To observe the adiabatic gas law, PV γ = const and measure the ratio of specific heats, γ, for
various gases.
Physical Principles
When a process occurs quickly enough that no heat is exchanged with the environment
(Q=0), the process is considered “adiabatic.” For such process, the relation between pressure
and volume is given by
(3.1a)
Here γ is the ratio of specific heats at constant pressure and constant volume, i. e.,
(3.2a)
A measurement of γ reveals important physical information about the structure of the gas
molecules. The equipartition theorem tells us that the molar specific heat at constant
volume is related to the number of degrees of freedom, f, available to each molecule
through the relation
(3.3a)
where f = 3 for a monatomic gas with three translational directions of motion, and f = 5 for a
diatomic gas with three translational plus two rotational contributions to the internal
energy.
const PV
= γ
V
P
c
c
= γ
R
f
c
V 2
=
Target Students
General physics, physics for scientists and engineers, physical chemistry, engineering
thermodynamics.