Capacitor Energy & Charge
Stored energy and charge at a given voltage.
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The engineering
Energy goes with the square of voltage — doubling V quadruples the stored joules, which is why bus caps bite harder than their size suggests. A 1000 µF cap at 400 V holds 80 J: enough to weld a screwdriver tip.
Bleed resistors exist because Q = CV doesn't care that the equipment is unplugged.
Where this math comes from
The Leyden jar — 1745, Ewald von Kleist and Pieter van Musschenbroek independently — was the first device that stored electricity, and it announced itself by knocking its discoverers across the room. Benjamin Franklin's analysis of the jar coined 'plus' and 'minus' charge.
Michael Faraday put capacitance on a measurable footing in the 1830s (the farad remembers him), and the ½CV² energy bookkeeping settled in with 19th-century field theory.
- 1745von Kleist & van MusschenbroekThe Leyden jar — first capacitor, discovered twice.
- 1752Benjamin FranklinCharge conservation analysis of the jar.
- 1837Michael FaradayDielectrics and the measure of capacitance.
See the full timeline of the math behind every calculator →
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