MadSci Network: Physics

Re: How does a glass rod becomes + charged when rubbed with a silk cloth?

Date: Mon Sep 7 16:38:58 1998
Posted By: Moataz Attallah, Undergraduate, Mechanical Engineering, American University in Cairo-Egypt
Area of science: Physics
ID: 904441678.Ph

Dear friend,

The first rule to be mentioned before the answer is the famous Franklin's model
of electric charge and matter. This rule says that the charge can neither be
created nor destroyed; it can only be transferred. This model includes more
points (law of conservation of charges) :
1-Matter contains two types of electric charge, called positive and negative.
Uncharged objects have equal amounts of each type of charges. When objects are
charged by rubbing, electric charge is transferred from one object to another.
After this rubbing process, one of the objects has excess positive more than the
2-As you know, alike charges repel, and unlike charges attract.

So simply, the answer to your question is that the charges are not induced on
the rubbed rod; they are just transferred from the cloth you are rubing with,
whether that was wool, cotton, or silk.

This phenomenon was described by both Franklin and Coulomb. Coulomb was more
accurate that he reached to a law linking the force between two charged bodies.
He used a device called Coulomb's torsion balance.

Since your question was specific to glass, I think this is enough. However, the
case differs if we have a conductor that we want to charge.

Waiting for feedback,

Moataz Attallah
Undergraduate Mechanical Engineering
The American University in Cairo-Egypt

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