Electrostatic Charging

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Most bodies are normally close to being electrically neutral. That means that the number of electrons on the body is equal to the number of protons. To charge a body, you have to transfer electric charge to or from it, so that the number of electrons is no longer equal to the number of protons. Since protons are fixed in the nucleus of the atoms, charging is a process of transfer of electrons:

Charging positively: Removal of electrons from an object.
Charging negatively: Addition of electrons to an object.

The typical number of electrons transferred in the electrostatic charging processes is of the order of 10⁹. Since one kg of material has about 10²⁵ atoms, only one in 10¹⁶ atoms loses an electron in the process. The atoms affected are the ones near the surface. Charging can be done via friction, conduction or induction.

Charging by friction: You have noticed that if you run a comb through dry hair, or take off a sweater on a dry day, you get static charge on the comb or the sweater, and they attract dust and small pieces of paper. The hair then has the unfortunate tendency to stand up! When a glass rod is rubbed with silk, the glass gets positively charged, and the silk gets negatively charged. Some electrons are transferred from the glass to the silk as a result of the rubbing. When an ebonite rod is rubbed with fur, the ebonite gets negatively charged, and the fur is positive. Rubbing or friction is an inefficient way of charging bodies: the amount of charge produced is low.
Charging by conduction: When a charged body is touched by an uncharged conductor, the original charge is shared between the two. The sign of charge on the body that is getting charged is the same as that on the original body.
Charging by induction: When a positively charged glass rod is brought close to an insulated piece of metal without touching it, free electrons of the metallic body are attracted towards the positive charge on the glass, and accumulate on the portion of the metallic body closest to the glass rod. The end of the metallic body far away from the glass rod is then left with lesser number of electrons, and is positively charged. Notice that the metallic body is still neutral overall - all that has happened so far is that the positive and negative charges have become separated, and accumulated on two different parts of the metallic body. If the metallic body is now grounded, electrons are conducted from the earth to the positive part of the metallic body, and neutralize the positive charges. If the glass rod is now removed, the net negative charge redistributes itself throughout the metallic body. The metallic body is thereby charged negatively. This is charging by induction. The glass rod, called the inducing body, did not touch the metal. The final charge left on the induced body (the metal) is opposite to that on the inducing body.