How does Lord Kelvin's water drop electrostatic generator work?

[brainpushups]

I recently made a small version of Lord Kelvin's "thunderstorm" while I was bored at school one day, and I'm still mystified as to how such a large potential gets generated. I have two hypotheses, but I haven't had a chance to test them yet and I was wondering if anybody knew how the generator works.

My first hypothesis was that perhaps ions in the water are pushed and pulled by the rings attached to the buckets and it is the ions that provide the potential difference. This seems improbable, but I was going to test the apparatus with deionized water just to see.

My other hypothesis takes into account the potential difference that exists between the lower buckets and the water source above it. I remember reading in Feynman's lectures a while ago that there exists about a 100V potential difference for every meter above the Earth (assuming flat ground with dry air or lots of ions present like above the ocean). Could the water actually be carrying this charge difference down with it? The water source is only half a meter (if that) above the lower buckets.

The apparatus has a 1.5cm spark gap made of tin foil that discharges every 10 or 15 seconds while its running. I haven't done the calculation, but I'm guessing this is on the order of magnitude of thousands of volts. Any ideas on how such a large potential difference builds up so quickly?

 

[cesiumfrog]

Is there something in http://en.wikipedia.org/wiki/Kelvin_water_dropper" that you want further clarification for?

 

[astrokreng]

Lord Kelvin's water drop electrostatic generator works by utilizing the phenomenon of electrostatic induction. This is the process by which a charged object can induce a charge on a nearby object without direct contact.

In the case of the water drop generator, the two metal rings attached to the buckets are charged with opposite charges, creating an electric field between them. When water droplets fall between the rings, they become polarized due to the electric field. This means that the positive and negative charges within the droplet are separated, with the positive charges being attracted to the negative ring and vice versa.

As the droplet falls, it passes through the electric field created by the rings, causing the separated charges to move in opposite directions. This creates a potential difference between the two buckets, with one bucket becoming positively charged and the other becoming negatively charged. This potential difference can reach thousands of volts, depending on the size and materials used in the generator.

Your first hypothesis, that the ions in the water are responsible for the potential difference, is partially correct. The polarized water droplets do contain ions that contribute to the charge separation. However, it is the electric field created by the charged rings that induces this charge separation, rather than the ions themselves.

Your second hypothesis, that the potential difference is due to the 100V/m potential difference described in Feynman's lectures, is also partially correct. The water source above the lower buckets does contribute to the potential difference, but it is not the only factor. The charged rings and the polarized water droplets also play a significant role in creating the potential difference.

In terms of the spark gap discharging every 10-15 seconds, this is due to the accumulation of charge on the buckets. As the buckets become more and more charged, the electric field between them becomes stronger, causing the spark to jump across the gap. This discharge helps to maintain the potential difference between the buckets.

In conclusion, Lord Kelvin's water drop electrostatic generator works by utilizing the principles of electrostatic induction to create a potential difference between two buckets. The charged rings and polarized water droplets play key roles in this process, and the accumulation of charge on the buckets leads to the occasional spark discharge.