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Name: Eric
Status: educator
Grade: 4-5
Country: USA
Date: Winter 2012-2013


Question:
My vague understanding of the triboelectric scale is that while materials by nature have a set number of protons and neutrons per atom, items closer to the top (positive) end of the scale have a much weaker hold on their neutrons and tend to lose them with little provocation, while items at the bottom (negative) part of the scale do not usually lose electrons and tend to pick up loose electrons as well. Hoping I have that right so far, then I have a question about lightning... For lightning to happen, a cloud has to become polarized, which means that it somehow loses some of its electrons. I see that air is at the top of the triboelectric scale, so I think that might be relevant, but a cloud is composed of air and water, so maybe I am thinking in the wrong direction. How does a cloud lose electrons to become polarized and set the stage for lightning to occur?

Replies:
Hi Eric,

I think you are moving toward the correct conclusion. Electrons are 1/2000 th the size of a proton and the tendency of e- to exist in quantum states are much more available to transfer.

There are two theories concerning triboelectric field generation and lightning: Polarization theory, where e- charges form from the magnetic field and are separated by falling ice/water; and the Cloud Particle Collision theory where ice and ice/water(graupel) rub together, the lighter ice flows upward with few e- charges(more positive) and the grauple falls, carrying the excess e-.. Both theories allow that negative charges(excess of e-) fall toward Earth.

The triboelectric series

( http://empl.ksc.nasa.gov/CurrentResearch/MECA/MECA.htm)

indicates that air is more positive and Earth materials such as apatite and bauxite tend to accept more e-. By either theory, the e- polarize and as such will tend to depolarize. Depolarization may be by diffusion events or by a mass transit event such as a electric spark(lightning). Depolarization may be ground to air, air to ground or air to air.

Hope this helps. Peter E. Hughes, Ph.D. Milford, NH


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