Capacitors: a tiny rechargeable bucket for charge
A capacitor is one of the simplest and most useful parts in all of electronics. At its heart it is just two metal plates placed close together but not touching. When you connect it to a battery, it quietly soaks up a little electric charge and holds it, like a small bucket holding water. Later it can pour that charge back out. It does not make energy and it does not use energy up the way a resistor does — it simply stores it and gives it back.
That one ability — store charge now, release it later — is behind a huge number of things: the smooth 5 volts feeding an Arduino, the tiny parts sprinkled next to every chip on a circuit board, the sudden flash of a camera, and the steady blink of an LED timer. By the end of this lesson you will understand what a capacitor is, how to read the numbers printed on one, how fast it charges, and what it is actually for.
What you will be able to do
- Explain what a capacitor is and how charging and discharging work.
- Understand capacitance and the farad, and convert between farads, microfarads, nanofarads and picofarads.
- Read the markings on electrolytic and ceramic capacitors — including the 3-digit ceramic code.
- Calculate the time constant $\tau = R \times C$ and use the 63% / 5-tau rule.
- Name the main jobs capacitors do: smoothing, decoupling, timing, filtering, energy storage.
- Combine capacitors in series and parallel — and stay safe around charged ones.
1. What is inside a capacitor?
Every capacitor is built from the same three ingredients:
- Two conductive plates — usually thin sheets of metal or metal film. These are where the charge sits.