\(E_{1}=\frac{k q}{\ell^{2}}=E_{2}\)
\(E_{3}=\frac{k q}{(\sqrt{2} \ell)^{2}}=\frac{k q}{2 \ell^{2}}\)
\(E=\frac{\sqrt{2} k q}{\ell^{2}}-\frac{k q}{2 \ell^{2}}=\frac{k q}{2 \ell^{2}}(2 \sqrt{2}-1)\)
$\left(\frac{1}{4 \pi \varepsilon_0}=9 \times 10^9\,N m ^2\,C ^{-2}, g=10\,m s ^{-2}\right)$