\(\mathrm{E}_{\max }=10^{6} \,\mathrm{V} / \mathrm{m}\)

\(\mathrm{C}=15\, \mu \mathrm{F}\)

\(\mathrm{C}=\frac{\mathrm{k} \varepsilon_{0} \mathrm{A}}{\mathrm{d}} ; \quad \frac{\mathrm{Cd}}{\varepsilon_{0} \mathrm{A}}=\mathrm{k}\)

\(\mathrm{k}=\frac{15 \times 10^{-12} \times 500 \times 10^{-6}}{8.86 \times 10^{-12} \times 10^{4}}=\frac{15 \times 5}{8.86}=8.465\)

\(k \approx 8.5\)