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 = Cp/Cv

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.