Conservation of electric charge and the process of charging

Conservation of charge governs every charging process: the total charge of an isolated system never changes, and any change in a single object's net charge results from electron transfer across its boundary.

Friction and Contact

• Charging by friction and by contact (conduction) both transfer electrons between surfaces.
• Friction produces equal and opposite charges on the two objects.
• Contact (conduction) leaves both objects with the same sign of charge.
• In all cases, the charge gained by one object equals the charge lost by the other, so the total charge is conserved.

Induced Charge Separation

Neutral objects can still respond to external charges through induced charge separation.

Conductors

• Free electrons are mobile and redistribute so that charge opposite to the external charge accumulates on the near side, while like charge is left on the far side.

Insulators

• Electrons remain bound, so the molecular electron clouds distort only slightly, producing a weak surface polarization.

Both effects create a net attractive force toward the external charge, because the unlike charge is induced closer to it than the like charge.

Grounding

Grounding exploits induction on a larger scale: connecting a conductor to Earth while an external charge is nearby allows electron transfer between the conductor and Earth. If the ground connection is removed while the external charge is still present, the transferred charge persists, leaving the conductor with a net charge opposite to the inducing charge.