ABSTRACT
The changes in pressure when a sound wave travels through the air are, in general, so rapid that heat cannot be exchanged between different volume elements. Consequently, the changes are adiabatic. When air, whose initial pressure and volume are P0 and V0 are changed to (P0 + p) and (V0 + dV), respectively, due to sound pressure p, the following relationship is obtained:
where y is the ratio of specific heats at constant pressure and constant volume. If V0 j LlV is very small, then expanding the right-hand side of the above equation and approximating, it follows that:
Putting
K = yP0 LlV
(10.1)
(10.2)
Therefore, sound pressure is proportional to volume change. K is called the 'bulk modulus of elasticity' or 'volume elasticity'.
