MCQ Detailed View

The correct answer is Pressure of air.

The velocity of sound in air depends mainly on the elastic properties of the medium and its density. In gases, the relationship is given by the formula:

v=γRTMv = \sqrt{\frac{\gamma RT}{M}}v=MγRT

Where:

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  $v$ = velocity of sound

  
  


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  $\gamma$ = ratio of specific heats (Cp/Cv)

  
  


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  $R$ = universal gas constant

  
  


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  $T$ = absolute temperature of the gas

  
  


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  $M$ = molar mass of gas

  
  

From this equation, it is clear that the velocity of sound in air depends directly on the temperature (T) and the composition of air (M), but not on the pressure (P).

Why does pressure not matter?

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  Both the elastic restoring force and the density of air change in the same proportion when pressure changes. This means their ratio, which determines the speed of sound, remains constant.

  
  


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  For example, whether the air is at sea level pressure (1 atm) or inside a pressurized chamber, the velocity of sound will be the same if the temperature and composition are constant.

  
  

On the other hand:

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  Temperature strongly affects sound speed — warmer air increases velocity because molecules move faster.

  
  


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  Moisture content also plays a role since water vapor is lighter than dry air, reducing the effective molecular weight of air and increasing sound velocity.

  
  


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  Wind can change the apparent speed of sound relative to the ground, especially if it blows in the same or opposite direction of propagation.

  
  

🔑 Key Facts:

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  Velocity of sound in air at 0 °C ≈ 331 m/s.

  
  


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  Increases by about 0.6 m/s per °C rise in temperature.

  
  


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  Independent of air pressure.

  
  


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  Affected by temperature, humidity, and wind conditions.

  
  

👉 Final Answer: The velocity of sound in air does not change with the change of air pressure.