What makes a Kelvin Generator work?

[Eternals]

I am wondering how a Kelvin water dropper works and can generate sparks. Basically, water drips onto two sides, and the apparatus attracts positive charge to one side and negative charge to another side. The charge eventually builds up high enough to make a spark. You can see more information about it here:
http://en.wikipedia.org/wiki/Kelvin_water_dropper

I can understand that general idea, but what I don't understand is where the positive and negative charge comes from. Isn't a single water molecule neutral? It would have (1 + 1 + 8 = 10) protons and also 10 electrons, so the net charge of a single molecule would be 0... So what would be making the buildup of charge?

 

[Borek]

Everything is explained in the wiki page you linked to, hard to add something to the description given there. Molecule of water is neutral, but solution is full of ions - single drop is neutral only on average, as it can easily contain few cations or few anions more. Then when the drop is created and falls it can get additionally charged due to friction.

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[quicknote]

A Kelvin generator, also known as a Kelvin water dropper, works through a process known as triboelectric charging. This occurs when two different materials come into contact and then separate, causing a transfer of electrons between them. In the case of a Kelvin generator, the two sides are made of different materials, typically metal and rubber, and the water droplets act as the "bridge" between them.

As the water droplets fall, they come into contact with the metal and rubber, causing the transfer of electrons from one material to the other. This creates a separation of charge, with one side becoming positively charged and the other becoming negatively charged. This separation of charge continues to build up as the water droplets continue to fall, ultimately creating a high enough potential difference to produce a spark.

It is important to note that although a single water molecule may be neutral, the water droplets in the Kelvin generator are made up of many molecules. As they come into contact with the different materials, the triboelectric effect causes the transfer of electrons between the materials and the water droplets, resulting in the buildup of charge.

In summary, a Kelvin generator works by utilizing the triboelectric effect to create a separation of charge between two materials, with the water droplets acting as the medium for this charge transfer. This buildup of charge ultimately leads to the production of sparks.