State what the capacitance of a parallel plate capacitor means.
A capacitor of capacitance $C$ is placed in the circuit shown in Fig. 7.1. When the two-way switch is in position A, the capacitor is charged until the potential difference across it is $V$. The switch is then moved to position B and the capacitor fully discharges through the sensitive ammeter. The switch is moved repeatedly between A and B so that the capacitor charges and discharges with frequency $f$. Show that the average current $I$ in the ammeter is given by the expression $I = fCV$.
When the potential difference is $150\,\text{V}$ and the frequency is $60\,\text{Hz}$, the average current in the ammeter is $4.8\,\mu\text{A}$. Calculate the capacitance, in pF, of the capacitor.
A second capacitor, with the same capacitance as the capacitor in (b), is added to the circuit of Fig. 7.1. The two capacitors are connected in series. State and explain the new ammeter reading.