A parallel–plate capacitor has plates of area 600 cm2 and a separation of 4 mm. The capacitor is charged to 100 V and is then disconnected from the battery.

(a) Find the electric field E0 and the electrostatic energy U. A dielectric of constant κ = 4 is then inserted, completely filling the space between the plates. Find

(b) The new electric field E,

(c) The potential difference V, and

(d) The new electrostatic energy.