MHT CET · Physics · Waves and Sound

The frequency of the third overtone of a pipe of length ' \(L_c\) ', closed at one end is same as the frequency of the sixth overtone of a pipe of length ' \(L_0\) ', open at both ends. Then the ratio \(\mathrm{L}_{\mathrm{c}}: \mathrm{L}_0\) is

A \(1: 4\)
B \(1: 2\)
C \(2: 1\)
D \(4: 1\)

Verified Solution

Answer & Solution

Correct Answer

(B) \(1: 2\)

Step-by-step Solution

Detailed explanation

Third overtone of pipe closed at one end
\(\mathrm{f}=\frac{(2 \mathrm{n}+1) \mathrm{V}}{4 l_1}=\frac{(2 \times 3+1) \mathrm{V}}{4 l_1}=\frac{7 \mathrm{~V}}{4 l_1}\)
Sixth overtone of pipe open at both ends
\(\begin{aligned}
& \mathrm{f}=\frac{\mathrm{nV}}{2 l_2}=\frac{7 \mathrm{~V}}{2 l_2} \Rightarrow \frac{7 \mathrm{~V}}{4 l_1}=\frac{7 \mathrm{~V}}{2 l_2} \\
& \frac{\mathrm{~L}_{\mathrm{c}}}{\mathrm{~L}_{\mathrm{o}}}=\frac{1}{2} \quad \ldots\left(\because \mathrm{l}_1=\mathrm{L}_{\mathrm{C}} \text { and } \mathrm{l}_2=\mathrm{L}_{\mathrm{O}}\right)
\end{aligned}\)

Apply the relevant identity from the chapter and substitute the values established in the previous step, keeping the original constraint in view.

Use the simplified expression to isolate the unknown, then plug the result back into the question setup to confirm the working is internally consistent.

Cross-check against a boundary or limiting case. Both the dimensional balance and the qualitative behaviour at the extreme should agree with the candidate answer.

Combine the steps above to identify the correct option. The remaining choices each fail at least one of the consistency, dimensional, or boundary checks.

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