An Ideal, Isolated, Air-Filled Parallel-Plate Capacitor Is Not Connected to a Battery

question 107

Short Answer

An ideal, isolated, air-filled parallel-plate capacitor is not connected to a battery but has equal and opposite charges of $3.9 \mathrm { nC }$ on its plates. The separation between the plates initially is $1.2 \mathrm {~mm}$ , and for this separation the capacitance is $3.1 \times 10 ^ { - 11 } \mathrm {~F}$ . How much work must be done to pull the plates apart until their separation becomes $7.7 \mathrm {~mm}$ ? $\left( \varepsilon _ { 0 } = \right.$ $\left. 8.85 \times 10 ^ { - 12 } \mathrm { C } ^ { 2 } / \mathrm { N } \cdot \mathrm { m } ^ { 2 } \right)$