RC Circuit
Definition
A circuit with a resistor and capacitor in series — the classic example of something that changes gradually over time.
Symbol: · Unit: s
Technical definition
A resistor-capacitor network whose charging/discharging follows exponential curves with time constant τ = RC. Capacitor voltage during charging: V(t) = V₀(1 − e^(−t/RC)). After ~5τ the capacitor is essentially fully charged.
Example
A 10 kΩ resistor with a 100 µF capacitor gives τ = 1 s — the capacitor charges to 63% in one second, ~99% in five seconds.
Common confusion
The capacitor never ‘finishes’ charging mathematically — it approaches full charge asymptotically. ‘Fully charged’ in practice means ~5 time constants, when it is within 1% of maximum.