b
(b)
In a closed pipe $f=\frac{(2 P+1)}{4 I} v$
For third overtone $(f)=\frac{7 v}{4 l}$
$\lambda=\frac{v}{f}=\frac{v}{7 v} \times 4 l$
$\lambda=\frac{4 l}{7}$
$\lambda=\frac{4 \times 105}{7}$
$\lambda=60 \,cm$
First pressure node will be formed $\frac{\lambda}{4}$
