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Capacitors store energy in an electric field between their plates, and inductors store it in a magnetic field around their winding. Both can release that energy quickly, which makes them essential for smoothing, filtering, timing, and pulsed-power circuits. The energy depends on the square of voltage (capacitor) or current (inductor), so doubling either quadruples the stored energy.
| Quantity | Capacitor | Inductor |
|---|---|---|
| Energy | E = ½CV² | E = ½LI² |
| Solve for value | C = 2E/V² | L = 2E/I² |
| Solve for V or I | V = √(2E/C) | I = √(2E/L) |
| Field type | Electric | Magnetic |
Energy is in joules when C is in farads, V in volts, L in henries, and I in amps.
E = ½CV², where C is in farads and V in volts, giving energy in joules. Doubling the voltage quadruples the stored energy.
E = ½LI², where L is in henries and I in amps. The energy is held in the magnetic field and depends on the square of the current.
Because the energy is the integral of instantaneous power as the voltage (or current) builds up from zero — that integration of a linear ramp gives the ½ factor.
Capacitors (especially supercapacitors) generally store far more energy per volume than inductors, which is why energy storage usually uses capacitors or batteries rather than inductors.
It can be — a large capacitor at high voltage (like a camera flash or power-supply bulk cap) stores enough energy to give a serious shock or burn. Always discharge before handling.
The inductor tries to maintain its current, producing a large voltage spike (the inductive kick). A freewheeling diode or snubber safely absorbs this energy.
Ideal ones do not, but real capacitors leak slowly and real inductors have winding resistance, so the energy gradually dissipates as heat.
Through a suitable resistor (not a direct short, which can damage it or arc). The resistor limits the current while the energy dissipates as heat.
The joule (J). One joule is one watt for one second; the calculator also shows mJ, µJ, and nJ for small values.
The inductor stores energy from the input during one part of the cycle and releases it to the output during the next — the ½LI² per cycle times frequency sets the power handled.
Yes — it can also be written E = ½QV = Q²/2C, since charge Q = CV. All three forms give the same energy.
Because both the stored charge (or flux) and the driving voltage (or current) rise together, so their product — the energy — grows as the square.
Reactance (XC & XL) • RC Time Constant • RLC Resonant Frequency • All Calculators