An Isolated Air-Filled Parallel-Plate Capacitor That Is No Longer Connected

Short Answer

An isolated air-filled parallel-plate capacitor that is no longer connected to anything has been charged up to Q = 2.9 nC. The separation between the plates initially is 1.20 mm, and for this separation the capacitance is 31 pF. Calculate the work that must be done to pull the plates apart until their separation becomes 5.30 mm, if the charge on the plates remains constant. (ε₀ = 8.85 × 10^-12 C²/N ∙ m²)