The formula for the vibration frequency of a sonometer wire is:
\(f = \frac{1}{2L} \sqrt{\frac{T}{\mu}}\)
For the initial tension:
\(f_1 = \frac{1}{2} \sqrt{\frac{6}{\mu}}\)
For the new tension:
\(f_2 = \frac{1}{2} \sqrt{\frac{54}{\mu}}\)
It is given that:
\(f_2 - f_1 = 12\)
The ratio of the frequencies is:
\(\frac{f_1}{f_2} = \frac{1}{3}\)
Upon substitution:
\(f_1 = 6 \, \text{Hz}\)