Mechanism of Charging of an Object - Charging by Friction

Charging by friction is one of the three basic methods (along with conduction and induction) by which a neutral object acquires an electric charge. It is the simplest and most commonly observed method of electrification in daily life.

Charging by friction is the process by which two different insulating (dielectric) materials become electrically charged — equal in magnitude but opposite in sign — when rubbed against each other, due to the transfer of electrons from one surface to the other.

Every atom is electrically neutral because it contains an equal number of positively charged protons (in the nucleus) and negatively charged electrons (orbiting the nucleus).

• Protons are tightly bound inside the nucleus and cannot move under ordinary conditions.
• Electrons, especially those in the outermost shell (valence electrons), are loosely bound and can be dislodged with relatively little energy.
• When energy is supplied (e.g., through rubbing/friction), these loosely bound electrons can be transferred from one atom/body to another.
• Only electrons move during charging. Protons never move between bodies — a body becomes positive only by losing electrons, never by gaining protons.

When two different insulating materials are rubbed together:

1. Friction supplies mechanical energy to the surface atoms of both materials.
2. This energy dislodges loosely bound valence electrons from the material with a weaker hold on its electrons.
3. These electrons are transferred to the material with a stronger affinity for electrons.
4. As a result, one body ends up with a surplus of electrons (negative charge) and the other with a deficit of electrons (positive charge).

Key Principle - Conservation of Charge: The charge gained by one body is exactly equal (in magnitude) to the charge lost by the other. Total charge of the isolated system remains conserved.