Question

An isolated air-filled parallel-plate capacitor that is no longer connected to anything has been charged up to Q = 3.4 nC. The separation between the plates initially is 3.4 mm, and for this separation the capacitance is 63 pF. Calculate the work that must be done to pull the plates apart until their separation becomes 6.7 mm, if the charge on the plates remains constant. (ε0 = 8.85 × 10-12 C2/N ∙ m2). Give you answer to the nearest 0.01 μJ.

Answer 1

work done = change in the energy stored in the capacitor

You can also solve by

1. Find the value of area

2. find new capacitance when plates are far

3. Use energy stored = Q^{​​​​​​2}/2C