Question

An organ pipe closed at one end resonates with forks of frequencies $180hZ$ and $300Hz$. lt will also resonate with tuning fork of frequencies

• A. $360Hz$
• B. $420Hz$
• C. $480Hz$
• D. $600Hz$

Answer 1

The correct option is B $420Hz$

For an organ pipe closed at one end
$f_n=\frac{(2n-1)v}{4L}$ .....(2) where f stands for for pipe closed at one end
The fundamental frequencies are odd multiple of first harmonic $\frac{v}{4L}$
The values given are $180$ and $300Hz$.
Both $180$ and $300$ are odd multiples of $60$( 3 times and 5 times respectively).
Hence, 1st harmonic is $60Hz$.

Only $420$ is odd multiple of $60$.