Kelvin water dropper

The Kelvin water dropper, [Sir William Thomson (Lord Kelvin), "On a self-acting apparatus for multiplying and maintaining electric charges, with applications to illustrate the voltaic theory," "Proceedings of the Royal Society of London," vol. 16, pages 67-72 (20 June 1867).] named for Lord Kelvin, is a type of electrostatic generator. Kelvin referred to the device as his water-dropping condenser. The device uses falling water drops to generate voltage differences by utilizing the electrostatic induction [Maryam Zaiei-Moayyed, Edward Goodman, and Peter Williams, "Electrical deflection of polar liquid streams: A misunderstood demonstration," "Journal of Chemical Education", vol. 77, no. 11, pages 1520-1524 (November 2000). cite web|url=http://jchemed.chem.wisc.edu/hs/journal/issues/2000/Nov/clicSubscriber/V77N11/p1520.pdf|title=Article in Journal of Chemical Education|format=PDF; subscription required|publisher=Division of Chemical Education of the American Chemical Society|year=2000 issue|month=November| accessdate=2007-04-02] occurring between interconnected, oppositely charged systems.

Water runs down from the top, with slightly positively-charged water attracted to the negative ring and slightly negative water attracted to the positive ring. The charged water flows through the ring and into a container. The charges then build up in the ring connected to the container opposite it - attracting even more charge. This results in a positive feedback loop. [cite web|url=http://www.csiro.au/helix/experiments/dhexpkelvin.shtml|title=www.csiro.au/helix/experiments/dhexpkelvin.shtml ] The apparatus can be extended to more than two streams of droplets. [Markus Zahn, "Self-excited a.c. high voltage generation using water droplets," "American Journal of Physics", vol. 41, pages 196-202 (1973).]

References

External links

* Video demonstrating Kelvin water dropper in operation: See YouTube.com at "Lecture 10, M.I.T. 8.02 Electricity & Magnetism, Spring [term] 2002": http://youtube.com/watch?v=RQX8I9ZWtPQ&feature=related . See the last 6 minutes of this video for operation of Kelvin water dropper. Printed material related to this video: See "MIT Open Courseware" website; specifically, assignment 4 of course 8.02, which is available here: http://ocw.mit.edu/OcwWeb/Physics/8-02Electricity-and-MagnetismSpring2002/DownloadthisCourse/index.htm . As is seen in the video, the water must be charged as the stream breaks into droplets. If one attempts to charge the stream before it breaks into droplets — and the outlet can have several streams, as in a shower head — any charge that's induced in the stream can flow backwards through the stream and into the reservoir instead of flowing onto the droplets, so that in effect, the system is short-circuited. Properly operated Kelvin devices can generate high voltages, resulting in large, long, frequent, and bright sparks.

* [http://amasci.com/emotor/kelvin.html Detailed description of device and how to build your own Kelvin water dropper.]