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JEE Main 2021 (16 Mar, Shift 2) · Organ Pipes & Resonance Tube

Organ Pipes & Resonance Tube question from JEE Main 2021 (16 Mar, Shift 2)

Q90JEE Main 2021 · 16 MAR · SHIFT 2Medium

Organ Pipes & Resonance Tube

A closed organ pipe of length L and an open organ pipe contain gases of densities ρ\rho1 and ρ\rho2 respectively. The compressibility of gases are equal in both the pipes. Both the pipes are vibrating in their first overtone with same frequency. The length of the open pipe is x3Lρ1ρ2\frac{x}{3} L \sqrt{\frac{\rho_1}{\rho_2}} where x is ___________. (Round off to the Nearest Integer)

Numerical answer type. Work it out, then open the answer.

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Answer: 4

  1. Speed v=Bρv = \sqrt{\frac{B}{\rho}}; same BB, so v2v1=ρ1ρ2\frac{v_2}{v_1} = \sqrt{\frac{\rho_1}{\rho_2}}
  2. Closed pipe first overtone: 3v14L\frac{3v_1}{4L}; open pipe first overtone: 2v22Lo=v2Lo\frac{2v_2}{2L_o} = \frac{v_2}{L_o}
  3. Equate: Lo=4L3v2v1=43Lρ1ρ2L_o = \frac{4L}{3}\frac{v_2}{v_1} = \frac{4}{3}L\sqrt{\frac{\rho_1}{\rho_2}}
  4. So x=4x = 4.
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