### Triboelectric Charging

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#### Triboelectric Charging

Video Transcript

Tribolectric charging is a charging process that typically involves rubbing two insulating objects together. The rubbing results in the transfer of electrons from the material with the smallest electron affinity to the material with the greatest electron affinity. The object with the greatest electron affinity gains electrons and becomes negatively charged; the other object loses electrons and becomes positively-charged.

A triboelectric series ranks materials based on their relative affinity for electrons. The diagram shows materials with the greatest electron affinity being highest on the charts. Suppose Material X becomes positively-charged when rubbed with cotton. X must have a lower electron affinity than cotton and would be placed lower than cotton on the chart. Material X becomes negatively-charged when rubbed with wool. Thus, X has a greater electron affinity than wool and would be placed above wool on the chart (and below cotton). Observations of this nature allow one to rank materials in a triboelectric series.

By performing triboelectric charging experiments with a collection of materials, you can produce your own triboelectric series. Consider these results for Materials W, X, Y, and Z. By mixing logic with our simple rule for the relationship between electron affinity and the charge acquired by two rubbed objects, we can rank these four materials according to their electron affinity.

I will analyze these results from top to bottom. From Rows 1 and 2, we know that both Y and Z must have a greater affinity than W. But we don't know how they compare to each other or to material X. From Row 3, we know X must have a greater affinity then Z. But we don't know how Y compares to X and Z. And from Row 4, we know Y has a lower affinity than Z. Thus we can finalize our rankings of electron affinity, greatest to least as ...
X > Z > Y > W.

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