Energia armazenada capacitor

Energy stored in a capacitor

A charged capacitor holds energy in its electric field. The energy comes out as E = ½ · C · V² (joules), and the charge is Q = C · V (coulombs). Notice that energy goes with the square of voltage, so doubling V quadruples E. Take an example: 1000 µF at 50 V → E = ½ · 10⁻³ · 50² = ½ · 10⁻³ · 2500 = 1.25 J. That sounds tiny, until you dump it fast. Release that 1.25 J in 1 ms and you get 1.25 kW; squeeze it into 1 µs and it's 1.25 MW. That is exactly why a discharged-by-accident capacitor can punch holes in screwdrivers, and why stun guns and camera flashes lean on them.

Applications

Camera flashes hold around 10 J and let it go in milliseconds. Defibrillators deliver 150–360 J over a few ms. Stun guns run small caps charged to kV. Supercapacitors in electric buses and KERS systems bank tens of kJ for regenerative braking. Audio crossovers rely on capacitors to block low frequencies. Inside power supplies, the bulk caps smooth ripple, and the energy they hold has to carry the load through hold-up time when the line drops out. One safety habit: drain large caps through a resistor before you touch anything.

FAQ

Why ½ and not full C·V²? While charging, voltage climbs linearly from 0 to V, so the average voltage across the process is only V/2. Half the work ends up in the field; the other half burns off in the charging resistor.

Capacitor vs battery? A cap gives you enormous instantaneous power but holds very little total energy (Wh). A battery flips that around, with massive energy and limited power. Supercaps land somewhere in the middle.

Does it lose energy stored on its own? Yes. Internal leakage resistance means a charged cap slowly bleeds itself down, taking hours to days for film or ceramic types and as little as minutes for some electrolytics.