Charge and static

All matter has charge, in the same way that all matter has mass. Atoms have no overall charge – they are neutral. This is because atoms contain equal numbers of protons and electrons. Electrons carry a negative electric charge and protons carry a positive electric charge.

Static

Electrons can be made to move from one object to another. However, protons do not move because they are tightly bound in the nuclei of atoms.

For example, when a plastic rod is rubbed with a duster, electrons are transferred from one material to the other. The material that gains electrons becomes negatively charged. The material that loses electrons becomes positively charged.

A plastic rod is covered in negative charges (electrons). It is adjacent to a duster covered in positive charges.

The duster picks up electrons from the rod. This leaves the rod with a positive overall charge and the duster with a negative overall charge.

Static charge occurs when electrons build up on an object. Static charge:

  • can only build up on objects which are insulators, eg plastic or wood
  • cannot build up on objects that act as conductors, eg metals

Conductors allow the electrons to flow away, forming an electric current.

When a static charge on an object is discharged, an electric current flows through the air. This can cause sparks. Lightning is an example of a large amount of static charge being discharged.