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Organ Pipes & Resonance Tube question from NEET 2026 (Re-neet)

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Organ Pipes & Resonance Tube

For sound waves, if the number of nodes for the 55th harmonic of an open-ended pipe is nn and that for the 99th harmonic of the same pipe with one of its ends closed is mm, the ratio nm\frac{n}{m} is

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Answer: (d)

  1. Open pipe, kkth harmonic: L=kλ2L = k\frac{\lambda}{2} with antinodes at both ends, so it has kk displacement nodes. 5th harmonic: n=5n = 5.
  2. Closed pipe, (2k−1)(2k-1)th harmonic: L=(2k−1)λ4L = (2k-1)\frac{\lambda}{4} has kk nodes (one at the closed end). 9th harmonic: 2k−1=9⇒m=52k-1 = 9 \Rightarrow m = 5.
  3. nm=55=1\frac{n}{m} = \frac{5}{5} = 1
  4. So the answer is (d) 1.
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