“A designer wants a capacitor that takes a high voltage. The plates are $5\ \text{mm}$ apart. She fits a plastic sheet with $K = 3$ and thickness $4\ \text{mm}$, but it leaves $1\ \text{mm}$ of air in all. Air sparks at $3.0 \times 10^{6}\ \text{V/m}$. At what voltage does the capacitor spark?” is available to Standard subscribers.