An air-filled parallel-plate capacitor has a surface area of 7.60 cm2, separated by a distance of 1.80 mm. A 20.0 V potential difference is applied to these plates.
(a) How much energy is stored in the capacitor?
(b) If we want to change the stored energy to 1.5 nJ by adding a dielectric, what dielectric constant should the dielectric material have?