Electron Transfer in Static Electricity

Static electricity occurs when this balance changes. The key is the transfer of electrons between objects.

Gaining and losing electrons

When certain materials are rubbed together, electrons can transfer from one surface to the other. In this process, electrons move between the objects; protons remain in their atomic nuclei.

The object that gains electrons becomes negatively charged, because it now has more negative charge than positive charge. The object that loses electrons becomes positively charged, because some of its negative charge has been removed, leaving an excess of positive charge.

Becoming positive therefore does not mean gaining protons. It means losing electrons.

For example, rubbing an acetate rod with a cloth can transfer electrons from the rod to the cloth. The rod becomes positively charged and the cloth becomes negatively charged. The direction of electron transfer depends on the materials: electrons do not always move onto the object being rubbed.

Electrons are transferred rather than created or destroyed. If the rod and cloth start neutral and electrons transfer only between them, their final charges are equal in size and opposite in sign. Every electron lost by the rod is gained by the cloth. On insulating materials, this imbalance can remain because the charge cannot readily flow away.

Explaining attraction and repulsion

Electron transfer also explains why rubbing objects can change the forces between them. Opposite charges attract; like charges repel. The positively charged acetate rod and negatively charged cloth therefore attract one another.

A plastic comb rubbed through hair provides another example. Electrons transfer from the hair onto the comb, leaving the comb negative and the hair positive. The hair strands have the same type of charge, so they repel one another and can spread apart.

The charged comb can also attract neutral scraps of paper. Neutral does not mean that the paper contains no charges: its positive and negative charges balance overall. Near the charged comb, these charges become slightly separated, with opposite charge nearer the comb. This produces an attraction even though the paper is still neutral overall.

How a static spark fits the same explanation

Walking across a carpet can transfer electrons between materials and leave your body charged. When you approach a metal door handle, charge may move suddenly between you and the handle. This discharge reduces the charge imbalance and can produce a small spark and a brief shock.

Charging builds up an imbalance by transferring electrons; discharging allows charge to move again and reduces that imbalance.