Kelvin Water Dropper
Lord Kelvin's thunderstorm: an electrostatic generator that builds kilovolts from nothing but falling water. Two streams of drops fall through cross-connected rings into buckets. A tiny random charge imbalance feeds back inductively until sparks jump the gap.
About this lab
Lord Kelvin's water dropper, invented by William Thomson (later Lord Kelvin) in 1867, is one of the simplest and most elegant electrostatic generators ever devised. It requires no moving parts beyond gravity and water — yet it can produce voltages exceeding 10,000 volts. The device works through a positive feedback loop: two streams of water fall through metal rings (inductors) into separate metal buckets (collectors). Each ring is electrically connected to the opposite bucket. Any tiny random charge imbalance — perhaps a single ion more on one side — gets amplified with every drop that falls.
The physics relies on electrostatic induction. When a bucket carries a small positive charge, its cross-connected ring repels positive ions from the forming water drop on the opposite side, giving that drop a net negative charge. This negatively charged drop falls into its bucket, making it more negative, which in turn induces an even greater positive charge on drops falling into the first bucket. The charges on both sides grow exponentially. The rate of voltage growth depends on the drip rate (charge delivered per second), the capacitance of the bucket-ring system, and leakage resistance.
Eventually the electric field between the two buckets (or between dedicated spark-gap electrodes) exceeds the dielectric breakdown strength of air — about 3 MV/m for small gaps, or roughly 30 kV/cm. At that point, a spark jumps the gap, discharging both buckets simultaneously. The process then begins again from the residual charge. This simulation models individual drops with stochastic charge assignment based on the induction field, realistic capacitive charging, and Paschen-curve-inspired breakdown thresholds.