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⚛️ Physics  ·  Kinetic Theory  ·  NEET & JEE

A closed rigid container has an ideal monatomic gas. Heat Q is supplied at constant volume, raising the temperature by ΔT. The fraction of heat that goes into increasing the rotational kinetic energy of the molecules is:

Answer: 0, since monatomic gas molecules have no rotational degrees of freedom.

  • A 0, since monatomic gas molecules have no rotational degrees of freedom
  • B 2/5, the fraction associated with two rotational degrees of freedom in a diatomic gas
  • C 3/5, the fraction associated with translational energy in a diatomic gas
  • D 1/2, an arbitrary even split between translational and rotational energy

Correct answer: A. 0, since monatomic gas molecules have no rotational degrees of freedom

Explanation: Monatomic gas molecules (treated as point masses) have no rotational degrees of freedom, so all the heat supplied at constant volume goes entirely into translational kinetic energy.

Maxwell-Boltzmann Speed Distributionspeed (v)fraction of moleculesv_pv_avgv_rmsv_p < v_avg < v_rms always, for any gas at any temperature

Not all gas molecules move at the same speed - the Maxwell-Boltzmann distribution shows the spread, with the most probable speed vp slightly less than the average vavg, which is slightly less than the root-mean-square speed vrms used in the pressure formula.

Concept context

Kinetic theory of gases connects molecular motion to pressure and temperature, explaining gas laws, specific heats, and molecular speeds.

Read the full Kinetic Theory notes →