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Velocity of sound in air does not depend on

  • A.Density of air
  • B.Temperature of air
  • C.Pressure of air
  • D.Humidity of air

Answer: C

The speed of sound in air does not depend on the Pressure of air.

For an ideal gas the speed of sound is

\[ \begin{aligned} v &= \sqrt{\frac{\gamma P}{\rho}} \\ &= \sqrt{\frac{\gamma R T}{M}} \end{aligned} \]

If the pressure rises at constant temperature, the density rises in the same proportion, so the ratio \(P/\rho\) and the speed stay the same. The speed therefore depends on temperature, not on pressure.

Density matters when it changes independently, and temperature raises the speed by about 0.6 m/s per degree Celsius. Humidity matters too: moist air is less dense than dry air at the same temperature and pressure, so sound travels slightly faster in it.

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