Question

In $1m$ long open pipe, what is the harmonic of resonance obtained with a tuning fork of frequency $480Hz$?

• A. First
• B. Second
• C. Third
• D. Fourth

Answer 1

The correct option is C

Third

Step 1: Given

Length of pipe: $l=1m$

Frequency of fork: $f=480Hz$

Velocity of sound: $v=330m/s$

Step 2: Formula Used

Frequency of $n^{th}$ harmonic in an open pipe: $f=\frac{nv}{2l}$

Step 3: Calculate the number of harmonic using the formula

$$\begin{gathered} 480=\frac{n\times 330}{2\times 1} \\ \Rightarrow n=\frac{2\times 480}{330} \\ \Rightarrow n\approx 3 \end{gathered}$$

Hence, third harmonic of resonance is obtained.