Electricity · Capacitors

Watch a capacitor charge and discharge

Follow the electrons, then connect their changing flow rate to the exponential graphs.

Learning goalExplain why current falls as charge builds up—or leaves—the plates.

Electron-transfer rate maximum

Latest circuit eventBattery connected · capacitor initially empty

Key idea: electrons move through the metal conductors. None cross the dielectric gap.

1 Change the circuit

Charging Current is largest at the start

The empty capacitor has no opposing p.d., so almost the full supply p.d. is across the resistor.

2 Change the time scale Resistance, R2.0 kΩ 200 Ω10 kΩ Capacitance, C470 μF 50 μF2000 μF Supply p.d., V₀6.0 V 1 V12 V Display speed1× Changes playback only—not the physics.

Changing a component starts a fresh run with an empty capacitor.

Time constantRC = 0.940 s

0.00τAt 1τ: charge and p.d. reach 63.2%.

Charge, Q0 C

Capacitor p.d.0.000 V

Current, I3.00 mA

Stored energy0 J

Live evidence

Open one graph and follow it closely

Each graph starts from the latest switch event. The moving point is the capacitor now.

Charge cannot jump

Switching circuits keeps the capacitor p.d. continuous.

Current is a rate

More electron-transfer events each second means a larger current.

The gap stays insulating

Electrons build up on plate surfaces; they do not cross the dielectric.