Kelvin's Water Dropper

Also known as “Kelvin's Thunderstorm,” this electrostatic generator works as follows:

  The flow rate from the top water reservoir (containing some NaCl) is reduced until separate drops fall through the two metal rings.
  Each ring is electrically connected to the conducting catch pan on the opposite side.
  Since the catch pans are electrically insulated from  each other, they will have a slight initial difference in charge.
  If the left catch pan (and right ring) are charged slightly - , then negative ions  in the water at the right dropper tip will be pushed up, leaving the water in the right tip slightly + charged. This process also leaves the water at the left dropper tip - .
  when the drop breaks away from the right dropper it will be slightly + . As this + drop falls into the right catch pan, the right pan will become more + .
  As more drops fall the process increases any initial charge difference.

A potential difference of several kilovolts is generated between the two poles within a few minutes. The capacitance of the system is small so the device does not generate an impressive spark, but the voltage is easily observed with an electrostatic voltmeter.

J4 top, add NaCl to water

Make sure to have two metal containers. Adjust the valve until you get a roughly uniform drop rate at each spout (they don't have to be exactly the same). To do so you may have to wiggle around the rubber tubing or move around the brass container.

To show the potential, connect an electrostatic voltmeter across the two metal containers. It will take around 10 minutes for a large potential to accumulate while the drops fall. For a flashy demo, connect the lightbulbs in series across the two metal containers.

PIRA DCS 5A40.70