Physics · Class 11

Change molecular mass and temperature

An equilibrium gas has a distribution of speeds. RMS speed comes from the mean squared speed and exceeds the mean speed, which in turn exceeds the most probable speed. Lighter molecules move faster at the same temperature.

Open the interactive experiment →

Change molecular mass and temperature

வாயுவின் மூலக்கூறுகளுக்கு வேகப் பரவல் உண்டு. ஒரே வெப்பநிலையில் குறைந்த மூலக்கூறு நிறைக்கு RMS வேகம் அதிகம்.

Key notes, relationships and model limits

Key relationship

vrms=√(3RT/M); vmean=√(8RT/(πM)); vmost=√(2RT/M).

Remember

Common trap

Mean squared speed is not the square of mean speed.

Model limits

Maxwell–Boltzmann equilibrium gas; molar mass is converted from g/mol to kg/mol. Classical nonrelativistic ideal gas.

What you will learn

Compare three statistical speeds and their mass-temperature scaling.

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 nitrogen M=0.028 kg/mol at 300 K, vrms≈516.96 m/s, mean speed≈476.29 m/s and most probable speed≈422.10 m/s.

Why this matters

The model connects change molecular mass and temperature with an observable reading. Check the equation and assumptions before applying it.

Before you start

SI units · algebra · graph reading

Check your understanding

How does RMS speed change if temperature becomes four times larger?

It quadruples
It doubles
It increases by √2

Read the explanation

vrms is proportional to √T at fixed molecular mass.

Course connection: Class XI Chapter 12. Consult the roadmap for CBSE, NEET, JEE Main and Advanced scope.