Voltage rating of a parallel plate capacitor is 500 V . Its dielectric can withstand a maximum electric field of $10^6 \mathrm{~V} / \mathrm{m}$. The plate area is $10^{-4} \mathrm{~m}^2$. What is the dielectric constant if the capacitance is 15 pF ? $\left(\right.$ given $\left.\varepsilon_0=8.86 \times 10^{-12} \mathrm{C}^2 / \mathrm{Nm}^2\right)$