Question

A resonance in air column of length $20cm$ resonates with a tuning fork of frequency $450Hz$. Ignoring end correction, the velocity of sound in air is

• A. $1020m/s$
• B. $720m/s$
• C. $620m/s$
• D. $820m/s$

Answer 1

The correct option is B $720m/s$

Let the air column be closed one. In closed organ pipe for fundamental node
of vibration, $\frac{\lambda }{4}=0.2\Rightarrow \lambda =0.8m$,
$v=n\lambda$
If we take the frequency of air column to be equal to tuning fork then,
$v=450\times 0.8=360m/sec$
If we take the frequency of air column to be twice that of tuning fork then
$v=900\times 0.8=720m/sec$