\(E =\frac{1}{4 \pi \varepsilon_{0}} \times \frac{ Q }{ L } \times \frac{1}{\left(\frac{\sqrt{3 L }}{2}\right)} \times(2 \sin \theta)\)
\(\tan \theta=\frac{\frac{ L / 2}{\sqrt{3} L }}{2}=\frac{1}{\sqrt{3}}\)
\(sin \theta=\frac{1}{2}\)
\(E =\frac{ Q }{2 \sqrt{3} \pi \varepsilon_{0} L ^{2}}\)
[Given : Permittivity of vacuum $\left.\epsilon_{0}=8.85 \times 10^{-12} C ^{2} N ^{-1}- m ^{-2}\right]$