A cell culture monitoring system uses a 15 μF15\ \mu\text{F}15 μF capacitor charged to a potential difference of 12.0 V as a backup power source. The initial charge stored is Q0 Q_0\,Q0 and the initial energy stored is E0E_0E0. During a power interruption, the capacitor discharges through a precision 400 kΩ400\ \text{k}\Omega400 kΩ resistor. The time constant of this discharge circuit is TTT. Which statement is correct?
The time constant TTT is 6.0 ms6.0\ \text{ms}6.0 ms.
The initial charge Q0Q_0Q0 is 18 μC18\ \mu\text{C}18 μC.
After a time 3T3T3T, the energy stored in the capacitor is E0e−3E_0 e^{-3}E0e−3.
After a time TTT, the potential difference across the capacitor is 4.4 V4.4\ \text{V}4.4 V.
63 exam-style questions on AQA A Level Physics Capacitance (A-level only), covering Capacitance (A-level only), Parallel plate capacitor (A-level only), Energy stored by a capacitor (A-level only), and Capacitor charge and discharge (A-level only). Each one has a worked solution and a mark scheme showing where the marks go.