9702 · 19.3
Discharging a capacitor
You've learnt that a capacitor can store electrical potential energy. Now, let's explore what happens when it releases this stored energy back into a circuit. This process is called **discharging**, and it's fundamental to understanding many electronic circuits, from camera flashes to smoothing power supplies. This pilot aligns with **Senpai Corner** A Level notes (2025–2027) for topic **19.3**.
Need to know
What you need to know
- When a capacitor is being charged, the electrons flow from the positive to negative plate.
- When the capacitor is being discharged through a resistor, the electrons flow back from negative plate to the positive plate until there are equal number of electrons on each plate.
- At the start of the discharge, the current is large and gradually falls to zero.
- As a capacitor discharges, the I, V and Q all decrease exponentially.
- This is represented by an exponential decay in the graph above.
Explanation
Discharging a capacitor
- When a capacitor is being charged, the electrons flow from the positive to negative plate.
- When the capacitor is being discharged through a resistor, the electrons flow back from negative plate to the positive plate until there are equal number of electrons on each plate.
- At the start of the discharge, the current is large and gradually falls to zero.
- As a capacitor discharges, the I, V and Q all decrease exponentially.