Physics · Class 11

Change the speed of sound in a gas

Sound propagation depends on a gas’s adiabatic compressibility and density. In an ideal gas their pressure dependence cancels, leaving temperature, molar mass and heat-capacity ratio. Warm or light gases transmit sound faster.

Open the interactive experiment →

Change the speed of sound in a gas

நல்லியல்பு வாயுவில் ஒலி வேகம் √(γRT/M). வெப்பநிலை அதிகமாயின் அல்லது மோலார் நிறை குறைந்தால் வேகம் அதிகம்.

Key notes, relationships and model limits

Key relationship

v=√(γp/ρ)=√(γRT/M); M is molar mass in kg/mol; molecular vrms=√(3RT/M).

Remember

Common trap

Sound speed is not the RMS speed of gas molecules.

Model limits

Small-amplitude adiabatic sound in an ideal gas; M converted to kg/mol, constant γ and negligible humidity. Sound speed is independent of pressure at fixed ideal-gas temperature and composition.

What you will learn

Relate adiabatic response and molecular properties to sound speed.

Try the experiment

Try both scenarios, change one control, and predict the result before checking the graph and readouts.

Think of it this way

Change one input while keeping the others fixed, as you would in a controlled experiment.

Worked example

For air approximated by M=0.029 kg/mol, γ=1.4 and T=300 K, v≈347.0 m/s. Doubling pressure at that same state temperature does not change this ideal value.

Why this matters

The model connects change the speed of sound in a gas with an observable reading. Check the equation and assumptions before applying it.

Before you start

SI units · algebra · graph reading

Check your understanding

If kelvin temperature quadruples for the same gas, what happens to sound speed?

It quadruples
It doubles
It stays constant

Read the explanation

Sound speed is proportional to √T.

Course connection: Class XI Chapter 14. Consult the roadmap for CBSE, NEET, JEE Main and Advanced scope.