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JEE Main 2025 Apr 7 Shift 2, Physics Q7: Law of Equipartition of Energy

JEE Main2025Apr 7, Shift 2Physics
Q.

The helium and argon are put in the flask at the same room temperature (300 K). The ratio of average kinetic energies (per molecule) of helium and argon is :

(Give : Molar mass of helium = 4 g/mol, Molar mass of argon = 40 g/mol)

  1. A

    1 : 10

  2. B

    10 : 1

  3. C

    1 :

  4. D

    1 : 1

Solution

By the equipartition theorem, the average kinetic energy of a molecule depends only on the temperature and the number of active degrees of freedom: .

Both helium and argon are monatomic gases, so each has translational degrees of freedom (rotational modes are inactive for point-like atoms). Molar mass does not enter this expression.

At the same temperature 300 K, , so the ratio is exactly .

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