(a)[3]
Derive an expression, in terms of $C_X$ and $C_Y$, for the combined capacitance $C_T$ of the capacitors in this circuit. Explain your reasoning.
(b(i))[2]
Two capacitors P and Q are connected in parallel to a power supply of voltage $V$. The capacitance of P is $200\,\mu\text{F}$. The capacitance $C_Q$ of Q can be varied between $0$ and $400\,\mu\text{F}$. When $C_Q = 0$, the total energy stored in the capacitors is $2.5\,\text{mJ}$. Show that the supply voltage $V$ is $5.0\,\text{V}$.
(b(ii))[3]
Calculate the total energy, in $\text{mJ}$, stored in the capacitors when $C_Q$ has its maximum value.
(b(iii))[2]
On Fig. 6.2, sketch how the total energy $E$ stored in the capacitors changes with $C_Q$, as $C_Q$ varies from $0$ to $400\,\mu\text{F}$.