Everything Science Grade 10

16.2 CHAPTER 16. ELECTROSTATICS

becoming charged is tribo-electric charging.

Step 2:Extract material properties

Locate the materials in the tribo-electric series. The key thing is to know

which is more positive and more negative in the series. Silk falls above

cotton in our table making it more positive in the series.

Step 3:Apply principles

We know that when two materials are rubbed the more negative one

in the series gains electrons and the more positive one loses electrons.

This means that silk will lose electrons and cotton will gain electrons.

A material becomes negatively charged when it has an excess of

electrons, thus the cotton, which gains electrons, becomes negatively

charged.

Note that in this example the numbers are made up to be easy to calculate. In the real
world only a tiny fraction of the charges would move from one object to the other, but the
total charge would still be conserved.

See simulation: ( Simulation: VPgsz at http://www.everythingscience.co.za))

The process of materials becoming charged when they come into contact with other mate-
rials is known as tribo-electric charging. Materials can be arranged in a tribo-electric series
according to the likelihood of them gaining or losing electrons.

If a material has equal numbers of positive and negative charges we describe it as being
neutral (not favouring positive or negative overall charge).

If a neutral material loses electrons it becomes electron deficient and has an overall positive
charge. If a neutral material gains electrons it has excess electrons and has an overall
negative charge. For this reason we describe the ordering of materials in the tribo-electric
series as more positive or more negative depending on whether they are more likely to lose
or gain electrons.

Amber

photos/amber_byJohnAlanElson_wikimedia.jpg

Photograph by John Alan Elson on wikimedia

262 Physics: Electricity and Magnetism