Laplace’s Correction

Laplace pointed out that the changes in pressure of air layers caused by passage of sound take place under adiabatic condition owing to the following reasons:

• Air is bad conductor of heat
• Compression and rarefactions caused by the sound are too rapid to permit heat to flow out during compression and flow in during rarefaction

Under adiabatic conditions

E= γP,

Where γ = C_p/C_v

Hence, v = √(γP/ρ)

For air, γ = 1.4. Therefore, at STP, speed of sound is

v = 333 ms^–1

This value is very close to the experimentally observed value.