Positive and negative charges

Atoms and electrons

All substances are made of atoms. These are often called particles. An atom is electrically neutral - has no overall electrical charge. However, each atom contains even smaller particles called electrons.

  • Each electron has a negative charge.
  • If an atom gains an electron, it becomes negatively charged.
  • If an atom loses an electron, it becomes positively charged.

Electrons can move from one substance to another when objects are rubbed together. You may have done this with a party balloon: if you rub a balloon on your sweater, you can get the balloon to stick to the wall or to your hair. This is because of static electricity.

Moving charges

Girl touching Van de Graaff static electricity generator
A Van de Graaff generator produces static electricity, which makes your hair stand on end

When you rub two different materials against each other, they become electrically charged. This only works for electrically insulated objects and not with materials like metals, which conduct. For example, if you rub an acetate plastic rod with a duster:

  • electrons move from the rod to the duster
  • the duster becomes negatively charged and the rod becomes positively charged

The opposite thing happens with a polythene rod:

  • electrons move from the duster to the rod
  • the rod becomes negatively charged and the duster becomes positively charged

In both examples, the materials gain an equal amount of charge but the charges are opposite (one material becomes negative while the other becomes positive).