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Question #84419

Difficulty: 5/10 | 🟢 Free

The Question

A classical dilute gas consisting of NN non-interacting particles, each of mass m (kg)m \text{ (kg)} and positive charge q (C)q \text{ (C)}, is maintained at an absolute temperature T (K)T \text{ (K)}. The gas is confined in the half-space z≥0 (m)z \ge 0 \text{ (m)} and is subjected to an external potential energy field given by U(x,y,z)=12α(x2+y2)+qE0zU(x,y,z) = \frac{1}{2}\alpha(x^2 + y^2) + qE_0 z, where α (J m−2)\alpha \text{ (J m}^{-2}\text{)} and E0 (V m−1)E_0 \text{ (V m}^{-1}\text{)} are positive constants. If kB (J K−1)k_B \text{ (J K}^{-1}\text{)} is the Boltzmann constant, what is the average total energy per particle of this gas in thermal equilibrium?

Options

  • A.

    72kBT\frac{7}{2} k_B T

  • B.

    3 k_B T

  • C.

    52kBT\frac{5}{2} k_B T

  • D.

    32kBT+qE0kBTα\frac{3}{2} k_B T + qE_0 \sqrt{\frac{k_B T}{\alpha}}

Check Your Answer

Correct Answer

Step-by-Step Solution

Explanation

How the Examiner Thinks

Intuition_Breaker

Train your brain to resist "obvious" answers that are designed to deceive your intuition.

Concepts Behind This Question

Equipartition Theorem|Maxwell-Boltzmann Distribution|Coulombic Central Force

Why This Question Is Tricky

Examiner Levers

Dimensional Analysis

Tests if the student verifies units/dimensions before selecting.

Difficulty Boost : +2

Common Mistakes

This question tests the fundamental application of the Equipartition Theorem and Maxwell-Boltzmann statistics beyond memorized formulas.

Students often blindly assign (1/2)kT to every degree of freedom, incorrectly treating the linear potential qE₀z as a standard quadratic degree of freedom (yielding 3kT) or ignoring the spatial potential energy entirely (yielding 5/2 kT or 3/2 kT).

The trap exposes the misconception that equipartition applies uniformly to all potential fields, whereas it strictly requires a quadratic dependence in the Hamiltonian; linear fields yield a full kT contribution.

Quick Facts About This Question

Question Information

SubjectPhysics
ChapterThermodynamics - Class 11 Part 2
ConceptEquipartition Theorem
Difficulty5
Cognitive Load6
Target Solve Time140 sec
AccessFree