\(v=2(v)\left[L_{2}-L_{1}\right] ;\) where \(v=\) frequency of tuning
fork and \(L_{1}, L_{2}\) are the successive column length.
\(\therefore \quad v=2 \times 320[73-20] \times 10^{-2}=339.2 \mathrm{ms}^{-1}=339 \mathrm{ms}^{-1}\)
(જયાં $ {I_0} $ થ્રેશોલ્ડ તીવ્રતા)