Electricity is a kind of energy stored inside atoms, the minute building blocks of which all things are made. Atoms themselves are made up of particles, including electrons, which have a negative electric charge, and protons, which have a positive electric charge. In normal atoms, there are the same number of electrons and protons, and so the charges cancel each other out. But when an atom loses or gains an electron, it becomes electrically charged, either positively (if it loses one) or negatively (if it gains one). The atom is then known as an ion. To make electricity, we must either make the atoms lose or gain electrons, or enable free electrons to move.

Static electricity

Static electricity is produced when two objects rub against each other: the electrons rub off from the atoms of one material on to the other, producing many ions. You can make static electricity by running a comb through your hair. The comb leaves a few of its electrons behind in the hair, so the comb now has a small positive charge. It can pick up small pieces of paper because it attracts the electrons in the paper’s atoms. If you comb your hair in a dark room then hold the comb close to your thumb, you will see a tiny spark. The release of electricity heats the air molecules (groups of atoms) between comb and thumb, producing a flash of light.

​​​​​​​An electric charge heating air molecules is exactly what happens—but on a much grander scale—when lightning strikes during a thunderstorm. Lightning is static electricity that suddenly leaps between clouds and the ground.

Electrons flow through a conducting wire when it is connected to a battery or generator. When the current is switched on, or a battery is connected, the electrons all move in the same direction. They flow only if they have a complete pathway of conductors called a circuit.

Battery

When the battery is connected to a circuit, a chemical reaction causes the rod to become positively charged and the bottom of the battery case to become negatively charged. So electricity flows along a conducting wire that connects the negative terminal (on the underside of the case) to the positive terminal (at the top of the battery).

Generator

A generator makes electricity by converting motion (kinetic energy) into electrical energy. It does so by using magnetism: a magnetic field moving near a wire causes electricity to flow along the wire. In a generator, an electromagnet (the rotor) rotates inside an electric coil (the stator). The effect induces (creates) an electric current when it is connected to a circuit.