Q121 / 150 · MHT CET 2011 · Physics
In a resonance tube the first resonance with a tunning fork occurs at $16 \mathrm{~cm}$ and second at $49 \mathrm{~cm} .$ If the velocity of sound is $330 \mathrm{~m} / \mathrm{s}$, the frequency of tunning fork is
- Correct answerA500
- B300
- C330
- D165
Solution
For closed pipe $l_{1}=\frac{v}{4 n}$ and $l_{2}=\frac{3 v}{4 n}$
$$
\begin{aligned}
v &=2 n\left(l_{2}-l_{1}\right) \\
n &=\frac{v}{2\left(l_{2}-l_{1}\right)} \\
&=\frac{330}{2 \times(0.49-0.16)}=500 \mathrm{~Hz}
\end{aligned}
$$
Hence, the correct answer is option: 'A'.