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Question #42866

Difficulty: 8/10 | 🟢 Free

The Question

A cylindrical string of length LL, cross-sectional area AA, and intrinsic linear mass density μ0\mu_0 is stretched with a constant tension TT between two rigid supports inside a closed chamber. The chamber is filled with an ideal monoatomic gas (γ=53\gamma = \frac{5}{3}). Due to the fluid's added mass effect, the effective linear mass density of the string during transverse vibrations is given by μeff=μ0+ρgA\mu_{\text{eff}} = \mu_0 + \rho_g A, where ρg\rho_g is the density of the gas. Initially, the gas has an energy density (internal energy per unit volume) of u0u_0 and a mass density of ρ0\rho_0. In this initial state, it is given that μ0=ρ0A\mu_0 = \rho_0 A, and the string's fundamental frequency is f0f_0. The gas is then rapidly and adiabatically compressed until its energy density becomes 32u032 u_0. Assuming LL, AA, and TT remain unchanged, what is the new fundamental frequency f1f_1 of the string?

Options

  • A.

    23f0\frac{\sqrt{2}}{3} f_0

  • B.

    233f0\sqrt{\frac{2}{33}} f_0

  • C.

    122f0\frac{1}{2\sqrt{2}} f_0

  • D.

    29f0\frac{2}{9} f_0

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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

Fundamental Frequency in Strings|Adiabatic Process Constraint|Wave Intensity and Medium

Why This Question Is Tricky

Common Mistakes

This question tests the student's ability to couple thermodynamics with wave mechanics by dynamically updating system constants.

The primary trap lies in the misapplication of the adiabatic constraint and the added mass effect.

Students often incorrectly assume that energy density scales linearly with density (an isothermal assumption, leading to ρ1=32ρ0\rho_1 = 32\rho_0) or they completely neglect the intrinsic mass of the string μ0\mu_0 when calculating the new wave speed.

By forcing the recalculation of the effective linear mass density μeff\mu_{\text{eff}} using the adiabatic relation P∝ργP \propto \rho^\gamma and the energy density relation u∝Pu \propto P, the problem penalizes rote application of the static string frequency formula and demands rigorous tracking of fluid-structure interactions.

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Question Information

SubjectPhysics
ChapterWaves - Class 11 Part 2
ConceptFundamental Frequency in Strings
Difficulty8
Cognitive Load7
Target Solve Time160 sec
AccessFree