Capacitors
Capacitors store charge in an electric field.
About this topic
A capacitor stores energy in an electric field between two conducting plates separated by an insulator. Capacitance C = Q/V, measured in farads, and the stored energy is ½CV². Larger plates, closer spacing and a good dielectric give more capacitance.
In an RC circuit the capacitor charges and discharges exponentially with time constant τ = RC. For example, a 100 microfarad capacitor with a 10 kilohm resistor has τ = 1 second, and after about five time constants it is effectively fully charged or discharged. A 1000 microfarad capacitor at 10 V stores ½ × 0.001 × 100 = 0.05 J.
Capacitors smooth power supplies, power camera flashes, tune radios and are used in touchscreens, where your finger changes the local capacitance. They release energy far faster than a battery, though they store much less.
A common misconception is that current flows through the insulator between the plates. Charge builds up on the plates, and current in the wires stops once the capacitor is charged. Also, a farad is huge, so most values are in microfarads or picofarads.
Key ideas
- C = Q/V
- Energy ½CV²
- Used in flash units and timing
Quick check
Use cases: where Capacitors helps
- Homework: review the key idea behind Capacitors before you start a problem set.
- Exam revision: use the quick check to test whether you can recall Capacitors without notes.
- Visual learning: play with the interactive lab to see how Capacitors changes when you adjust its inputs.
- Teaching a friend: explain Capacitors in your own words, then compare your version with the key ideas.
The same laws describe car crashes, sports, satellites and everyday machines.
Frequently asked questions
What is Capacitors?
Capacitors store charge in an electric field.
What will I learn in Capacitors?
C = Q/V. Energy ½CV². Used in flash units and timing.
Is Capacitors part of Physics?
Yes. It is one of 150 Physics topics on LearnViz HighSchoolEdu, with 3 key ideas, a live animation and a quick check.
Does the Capacitors lab work on a phone or tablet?
Yes. The animation resizes to fit your screen and supports touch, so you can drag, tap and slide with your finger.
How should I study Capacitors?
Read the summary and key ideas first, play with the interactive lab to see the idea in motion, then answer the quick check. If you get a question wrong, go back to the key idea it tests.
Do I need an account, and is my progress saved?
No account is needed. Marking a topic as learned is saved in your own browser, so it stays on that device and is not sent to a server.