NEET • Physics

Heat & Thermodynamics

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Translational KE and Molecular Speeds

The source lists translational kinetic energy of gas, RMS speed, average speed, and most probable speed.

K=12M⟨V2⟩=32PV=32nRTK=\frac{1}{2}M\langle V^2\rangle=\frac{3}{2}PV=\frac{3}{2}nRT
⟨V2⟩=3Pρ\langle V^2\rangle=\frac{3P}{\rho}
Vrms=3Pρ=3RTMmol=3KTmV_{rms}=\sqrt{\frac{3P}{\rho}}=\sqrt{\frac{3RT}{M_{mol}}}=\sqrt{\frac{3KT}{m}}
Vˉ=8KTπm=1.59KTm\bar V=\sqrt{\frac{8KT}{\pi m}}=1.59\sqrt{\frac{KT}{m}}
Vp=2KTm=1.41KTmV_p=\sqrt{\frac{2KT}{m}}=1.41\sqrt{\frac{KT}{m}}

Notes

  • The source notes Vrms∝TV_{rms}\propto\sqrt{T} and Vrms>Vˉ>VmpV_{rms}>\bar V>V_{mp}.