\(T \sin \theta=\frac{ kq ^{2}}{ x ^{2}}\)
\(\tan \theta=\frac{k q^{2}}{x^{2} m g}\)
as \(\tan \theta \approx \sin \theta \approx \frac{x}{2 L}\)
\(\frac{ x }{2 L }=\frac{ Kq ^{2}}{ x ^{2} mg }\)
\(x=\left(\frac{q^{2} L}{2 \pi \varepsilon_{0} m g}\right)^{1 / 3}\)