Walker, Halliday & Resnick — Capacitance: Problem 33

33 If an uncharged parallel-plate capacitor (capacitance \(C\)) is connected to a battery, one plate becomes negatively charged as electrons move to the plate face (area \(A\)). In Fig. 25-32, the depth \(d\) from which the electrons come in the plate in a particular capacitor is plotted against a range of values for the potential difference \(V\) of the battery. The density of conduction electrons in the copper plates is \(8.49 \times 10^{28} \text{ electrons/m}^3\). The vertical scale is set by \(d_s = 2.00 \text{ pm}\), and the horizontal scale is set by \(V_s = 20.0 \text{ V}\). What is the ratio \(C/A\)?