Capacitors
A capacitor stores energy in an electric field between two plates separated by an insulator. Its defining habit is resisting sudden changes in voltage. Charge one up and it holds that voltage for a while, like a small, fast-acting reservoir. Capacitance is measured in farads, but a whole farad is huge; practical parts run from picofarads (pF) through nanofarads (nF) to microfarads (µF).
The most useful way to understand a capacitor is by frequency: it blocks DC but passes AC. Once charged, no steady current flows through it. A changing voltage, though, pulls charge in and out of the plates continuously, so fast signals get through easily. That’s why capacitors can smooth a wobbly supply rail, couple a signal between stages while stripping off its DC level, or shunt high-frequency noise to ground.
On real boards, chemistry matters. Small ceramic capacitors are cheap, fast, and non-polarized. Electrolytics give you big values for bulk energy storage but are polarized. Install one backwards and it can fail dramatically, sometimes venting or popping. The stripe on the can marks the negative lead. Respect it.
Key points
- Capacitors store energy in an electric field and resist sudden voltage changes.
- They block DC but pass AC, which is the key to filtering, coupling, and smoothing.
- Practical values run from pF through nF to µF. A full farad is enormous.
- Electrolytic capacitors are polarized. Reverse one and it fails, sometimes violently.
Practice
0 of 2 answered · Not startedWrong answers just let you try again, and hints are there if you want them. Answering every question first time, without hints, is what earns mastery.
- 1
Why can a 10 µF ceramic capacitor behave like far less than 10 µF in a circuit?
- 2
What is the defining behaviour of a capacitor in a circuit?
