\(\text { (Third harmonic) }=3 \times v_{0}^{\prime}=3 \times \frac{v}{2 L^{\prime}}\)
First overtone of a closed organ pipe
\(\text { (Third harmonic) }=3 \times v_{0}=3 \times \frac{v}{4 L}\)
According to question,
\(3 v_{0}^{\prime}=3 v_{0} \Rightarrow 3 \times \frac{v}{2 L^{\prime}}=3 \times \frac{v}{4 L}\)
\(\therefore \quad L^{\prime}=2 L\)
$(a)$ $\left(x^2-v t\right)^2$
$(b)$ $\log \left[\frac{(x+v t)}{x_0}\right]$
$(c)$ $e^{\left\{-\frac{(x+v t)}{x_0}\right\}^2}$
$(d)$ $\frac{1}{x+v t}$