Polystyrene has dielectric constant 2.6 and dielectric strength 2.0 × 107 V/m . A piece of polystyrene is used as a dielectric in a parallel-plate capacitor, filling the volume between the plates.

a- When the electric field between the plates is 77 % of the dielectric strength, what is the energy density of the stored energy?

Express your answer with the appropriate units

b- When the capacitor is connected to a battery with voltage 500.0 V , the electric field between the plates is 77 % of the dielectric strength. What is the area of each plate if the capacitor stores 0.25 mJ of energy under these conditions?

Express your answer with the appropriate units