Question

The two nearest harmonics of a tube closed at one end and open at other end are $220\, Hz$ and $260\, Hz$ . What is the fundamental frequency of the system ?

• A. 20 Hz
• B. 30 Hz
• C. 40 Hz
• D. 10 Hz

Answer 1

Answer: (A)

20 Hz

Answer 2

Sol. Two successive frequencies of closed pipe $\frac{n v}{4 l}=220$...(i) $\frac{(n+2) v}{4 l}=260$...(ii) Dividing (ii) by (i), we get $\frac{n+2}{n}=\frac{260}{220}=\frac{13}{11}$ $11 n+22=13\, n$ $n=11$ So, $11 \frac{v}{4 I}=220$ $\frac{v}{4 l}=20$ So fundamental frequency is $20\, Hz$.