Capacitors
Simple Explanation
A capacitor is a device that stores electrical charge (and energy) on two conductive plates separated by an insulator — when connected to a voltage source, one plate accumulates positive charge and the other an equal negative charge.
Why Do We Need It?
Capacitors are essential components in nearly every electronic circuit — from smoothing power supplies to storing energy for camera flashes — making them one of the most widely used electrical components after resistors.
See It
A schematic of a capacitor showing two parallel plates connected to wires, with the left plate labelled positive charge and the right plate labelled negative charge, and the voltage V marked across them
Worked Example
Identify what happens when a capacitor is connected to a battery
A capacitor with both plates initially uncharged is connected to a 9 V battery. Describe what happens.
Why Does This Work?
The insulating gap between the plates prevents charge from directly flowing across, so charge instead builds up on each plate's surface — an electric field forms in the gap between the accumulated charges, and this field (and the stored charge) persists even after the battery is disconnected.
Real-Life Example
A camera's flash capacitor
A camera flash charges a capacitor slowly (over a second or two) from the battery, then discharges it almost instantly to power the bright flash.
The capacitor stores energy gradually but can release it far faster than the battery alone could supply, which is exactly what a sudden, bright flash requires.
Practice
What happens to the two plates of a capacitor when it is connected to a battery?
EasyCommon mistake
Assuming a capacitor lets current flow through it continuously, like a wire — a capacitor's insulating gap blocks any actual charge from crossing between the plates; it only stores charge on each plate separately.
Quick Review
- A capacitor stores charge and energy on two plates separated by an insulator.
- The two plates accumulate equal and opposite charge.
- Used throughout electronics — power smoothing, energy storage, timing circuits.