Question

In a resonating air column, the first booming sound is heard when the length of air column is $10cm$. The second booming sound will be heard when length is:

• A. $20cm$
• B. $30cm$
• C. $40cm$
• D. None of the above

Answer 1

The correct option is B $30cm$

Booming sound indicates that at that length, $l_1$, the air column is in resonance with the given frequency.
and that length is,
$l_1=\lambda /4=10$
or, $\lambda =40cm$
The next resonance length will be :
$l_2=3\lambda /4=30cm$