Physics 9702 · AS & A Level · Discharging a capacitor
Discharging a capacitor — practice question
A capacitor with capacitance $C$ and a resistor with resistance $R$ are arranged as shown in Fig. 6.1. At the beginning, the capacitor is charged and the switch is open. The switch is then closed at time $t = 0$. Fig. 6.2 and Fig. 6.3 show, respectively, how the charge $Q$ on the capacitor and the potential difference (p.d.) $V$ across the resistor vary with $t$.
(a)[3]
Explain the shape of the line in Fig. 6.3 that shows how $V$ varies with $t$.
(b)[3]
Use Fig. 6.2 to demonstrate that the time constant of the circuit in Fig. 6.1 is $5.5\,\text{s}$.
(c(i))[2]
Use Fig. 6.2, Fig. 6.3 and the information in (b) to work out the capacitance $C$, in $\mu\text{F}$.
(c(ii))[2]
Use Fig. 6.2, Fig. 6.3 and the information in (b) to work out the resistance $R$, in $\text{k}\Omega$.
Worked solution & mark scheme
This 10-mark question has a full step-by-step worked solution and mark scheme. One marking point: “p.d. across resistor is the same as p.d. across capacitor” …