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Question #43783

Difficulty: 8/10 | 🟢 Free

The Question

A hypothetical atom consists of a massive stationary nucleus of radius RR and total charge +Q+Q. The charge within the nucleus is distributed with a spherically symmetric volume charge density ρ(r)=cr\rho(r) = c r for r≤Rr \le R, where cc is a positive constant. A particle of mass mm and charge −q-q orbits the nucleus in a circular path of radius rnr_n (where rn<Rr_n < R). Assuming the Bohr quantization condition for angular momentum is valid for this system, the time period TnT_n of the particle in the nthn^{\text{th}} allowed orbit is proportional to nxn^x. What is the value of xx?

Options

  • A.

    −15-\frac{1}{5}

  • B.

    25\frac{2}{5}

  • C.

    35\frac{3}{5}

  • D.

    75\frac{7}{5}

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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

Quantization of Angular Momentum|Impact Parameter Geometry|Approximations

Why This Question Is Tricky

Common Mistakes

This question tests the student's ability to derive orbital parameters from first principles rather than relying on memorized formulas for the hydrogen atom.

The primary trap lies in assuming a standard Coulombic potential (V∝1/rV \propto 1/r) or a uniform charge density (ρ=const\rho = \text{const}), which lead to incorrect dependencies (T∝n3T \propto n^3 or T∝n0T \propto n^0 respectively).

By introducing a non-uniform charge density ρ(r)∝r\rho(r) \propto r, the effective potential Veff(r)=L22mr2+U(r)V_{eff}(r) = \frac{L^2}{2mr^2} + U(r) is fundamentally altered.

Students must correctly apply Gauss's Law to find the new force law (F∝r2F \propto r^2) and couple it with the angular momentum quantization condition to find the non-linear shift in the orbital radius and time period.

Quick Facts About This Question

Question Information

SubjectPhysics
ChapterAtoms - Class 12
ConceptQuantization of Angular Momentum
Difficulty8
Cognitive Load7
Target Solve Time160 sec
AccessFree