STANDARDPhysics-Thermodynamics

STANDARD Physics Degrees of Freedom Assertion Reason Question

Type: Assertion Reason-conceptual-Medium-Class 11

Assertion: Each vibrational mode gives two degrees of freedom. Reason: By law of equipartition of energy, the energy for each degree of freedom in thermal equilibrium is 2kgT.

A

If both assertion and reason are true and reason is the correct explanation of assertion.

B

If both assertion and reason are true but reason is not the correct explanation of assertion.

C

If assertion is true but reason is false.

D

If both assertion and reason are false.

Correct Answer

Option C

Detailed Explanation

By law of equipartition of energy, the energy for each degree of freedom in thermal equilibrium is 12kBT\frac{1}{2} k_B T. Each quadratic term form in the total energy expression of a molecule is to be counted as a degree of freedom. Thus each vibrational mode gives 2 degrees of freedom i.e., kinetic and potential energy modes, corresponding to the energy 2(12kBT)=kBT2 \left( \frac{1}{2} k_B T \right) = k_B T.

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