The Kelvin Water-drop Electrostatic Generator

The Physics Factbook™
Edited by Glenn Elert -- Written by his students
An educational, Fair Use website

topic index | author index | special index

Abstract

The purpose of this project is to re-create Lord Kelvin's water-drop electrostatic generator, also known as "Kelvin's Thunderstorm".

Introduction

Water is made up of mobile polar molecules. By bringing a positively-charged object close to a water dropper, the water droplets, and also their container, will acquire a negative charge due to induction. There is now voltage due to the separation of charge between the drop and the droplet container. To make a self-sustaining electric generator, an additional water dropper-container system needs to be substituted for the positively-charged object. In the example given above, a positively-charged object was used to induce negative droplets in the container. Therefore, a negatively-charged object can similarly be used to induce positive droplets in another container. By wiring the positive container to a conductor, this will effectively duplicate the effect of a positively-charged object's presence. The same can be done with the negative container and another conductor.

Diagram

Procedure

1. Set up the equipment as shown in the diagram. Make sure the connecting wires do not touch each other.
2. Charge one of the top cans with a sufficiently high voltage. (At first, we tried to provide the charge using an ebonite rod rubbed on animal fur, but it wasn't sufficient. We then used a 100,000 volt Van de Graff generator to charge an ebonite rod covered in aluminum foil. This provided a sufficient voltage for the electrostatic generator to produce electricity.)
3. The voltage in the top cans was then measured using a voltmeter and recorded.
4. Set the burets to drip the water droplets at a moderate speed.
5. After a while the voltage in the bottom two cans was measured and recorded using a voltmeter.
6. The voltage in the bottom can and the ground was then recorded in order to ensure that the voltages we were getting were actually from the water droplets and not just from the other can.
7. Steps 2-6 were repeated five times

Below is a data table that contains our initial and final voltages in our five trials.

Conclusion

The water-drop generator worked since it produced a small (~7 mV) increase in voltage from the initial voltage.

Genna Ableman, Harvey Lei, Brittany Mejia, David Rozenberg -- 2005

Another quality webpage by Glenn Elert		home | contact bent | chaos | eworld | facts | physics
share