What a learner can do afterwards
- Uses C = Q over V and works comfortably in microfarads and nanofarads
- Finds the stored energy from the area under a charge-voltage graph and from half CV squared
- Explains why the energy is not QV, arguing from the graph rather than from the formula
1 · Read
Capacitance is the charge a part holds per volt: C equals Q over V, in farads. Real labels use microfarads and nanofarads, meaning ten to the minus six and ten to the minus nine.
A defibrillator stores hundreds of joules in a capacitor, then delivers the charge at once. The same idea keeps a calculator's memory alive and fires a camera flash.
Stored energy is half of Q V, which also reads half C V squared or Q squared over 2 C. It is not Q V, because the first charge arrives at zero volts and the last at full volts, so the average is V over 2.
Read the energy as the area of a triangle under the charge against voltage line, not a rectangle. Doubling the voltage quadruples the stored energy, since V is squared.
Capacitors hold charge per volt, and filling them banks half of Q V.
2 · Watch
Take it off screen
Where it sits
Where this leads
Jobs that lean on this skill. Follow one to see everything it is built on.
8 questions wait behind this lesson, each with its answer explained. Every answer feeds the sky: stars light as they are learned, and dim when it is time to come back.