Question

How much energy can be stored in a capacitor with two parallel plates, each with an area of 64.0 cm2 and separated by a gap of 1.30 mm, filled with porcelain whose dielectric constant is 7.0, and holding equal and opposite charges of magnitude 420. μC?

Answer 1

Find the capacitance:

$$C=\frac{k\epsilon_0A}{d}.$$

The energy stored is

$$E=\frac{Q^2}{2C}=\frac{Q^2d}{2k\epsilon_0A}=28.9\text{ kJ}.$$