⚡ Capacitor Charge and Time Constant Calculator

Analyze capacitor charging and discharging behavior in RC circuits. Calculate time constants, voltage curves, energy storage, and visualize exponential responses.

Calculation Mode

Circuit Parameters

Interactive RC Circuit

Results & Analysis

Select calculation mode and enter values to see results

Voltage vs Time Curve

Capacitor Fundamentals

A capacitor stores electrical energy in an electric field. When charging through a resistor, the voltage follows an exponential curve governed by the time constant τ = RC.

V(t) = V₀(1 - e^(-t/τ))
Charging: voltage approaches supply voltage exponentially
V(t) = V₀e^(-t/τ)
Discharging: voltage decays exponentially to zero

Time Constant (τ)

The time constant τ = RC determines how quickly a capacitor charges or discharges:

  • 63.2% charged/discharged after 1τ
  • 86.5% charged/discharged after 2τ
  • 95.0% charged/discharged after 3τ
  • 98.2% charged/discharged after 4τ
  • 99.3% charged/discharged after 5τ

Applications

  • Timing Circuits: Delays, oscillators, pulse generators
  • Filtering: Smoothing power supplies, signal conditioning
  • Energy Storage: Flash photography, motor starting
  • Coupling: AC signal transmission, blocking DC
  • Memory: DRAM cells, backup power systems

HOW TO USE

Enter the supply voltage, resistance, and capacitance values. Select the time point and click Calculate to see the voltage across the capacitor at that instant.

FORMULA USED

Charging: V(t) = Vs × (1 - e^(-t/RC))
Discharging: V(t) = V₀ × e^(-t/RC)
Time constant τ = R × C

WORKED EXAMPLE

A 100μF capacitor charging through 10kΩ to 12V: τ = 10000 × 0.0001 = 1 second. At t=1s: V = 12 × (1 - e⁻¹) = 7.58V.

FREQUENTLY ASKED QUESTIONS

Q: What is the RC time constant?

A: τ = R × C in seconds. After 1τ, a capacitor charges to ~63.2% of supply voltage. After 5τ, it is considered fully charged (99.3%).

Q: How long does a capacitor take to fully charge?

A: Practically, a capacitor is considered fully charged after 5 time constants (5τ = 5 × R × C seconds).

Q: What happens when a capacitor is fully charged?

A: No more current flows. The capacitor acts as an open circuit in DC steady state.

Q: Can a capacitor charge instantly?

A: No. Without resistance, charging would be theoretically instantaneous but infinite current would flow, damaging the circuit.