Question

The equation a=-ρ\(\frac {da}{d\rho }\) where a is the speed of sound in the medium is the mathematical expression derived for the sound waves, which are _________

(a) Isentropic

(b) Incompressible

(c) Adiabatic

(d) Reversible

This question was posed to me in an interview.

This intriguing question originated from The Basic Normal Shock Equations topic in section Normal Shock Waves of Aerodynamics

Answer 1

The correct answer is (a) Isentropic

For explanation: The equation a=-ρ\(\frac {da}{d\rho }\) is the equation for the speed of sound in the medium. This is derived from the governing equations for sound waves, which are isentropic (adiabatic and reversible). Sound waves may or may not be compressible.