RC Capacitor Discharge

V = V_{0} \, e^{-t/\tau}

V =

V_0 =

t =

τ =

Enter your known values, leave one input blank, and solves for the missing one. Try different units for next level excitement!

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A discharging capacitor loses the same fraction of its remaining voltage in every time constant — down to about 37% after one τ, 14% after two, and so on. It is exactly the mathematics of radioactive half-life, just with a different clock. This lingering charge is why power supplies and camera flashes can bite long after being unplugged: with a large τ, "off" can still mean hundreds of volts.

RC Capacitor Discharge

V = V_{0} \, e^{-t/\tau}

Where

$V$ = Voltage at time t
$V_{0}$ = Initial voltage
$t$ = Elapsed time
$\tau$ = Time constant

Missing one of these? Work it out first, then come back

Voltage at time t — Ohm's Law, Electrical Power (P = VI)
Initial voltage — Ohm's Law, Electrical Power (P = VI)
Elapsed time — Half-Life Decay, Exponential Growth by Doubling Time
Time constant — RC Time Constant, RL Time Constant (τ = L/R)

Part of this formula set

Reactance, resonance and time constants

7 formulasHow capacitors and inductors oppose alternating current, the frequency at which they cancel, and the RC and RL constants that set switching speed.