# Electricity and magnetism

• You are here:

# Electricity

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. To make electricity, we must either make the atoms lose or gain electrons, or enable free electrons to move.

## Static electricity

In static electricity, the electrons do not move. It is produced when two objects rub against each other: the electrons rub off from the atoms of one material on to the other.

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, or from one cloud to another. Thunder is the noise of the air expanding rapidly in the intense heat.

## Current electricity

Electricity is the movement of electrons, the negative particles around the nucleus of an atom. Electricity flows in a current when electrons are free to move through a material. Most metals, especially silver and copper, have electrons that can move easily, so they are good carriers or conductors of electricity.

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. Electric current is measured in amperes (amps): the rate at which electricity flows through a conductor.

## Ohm's law

As electricity moves along a conductor, it meets a certain amount of opposition. This is called resistance. The amount of current in a circuit depends on both the amount of voltage—the force needed to push the electrons along—and the amount of resistance in the circuit (for example, that created by a filament in an electric light bulb) that opposes the current. This relationship between current, voltage and resistance is known as Ohm's Law. It states that resistance equals voltage divided by current.

## Batteries

Inside a dry battery like the one pictured here, there is a rod surrounded by chemicals. 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).

## Insulators

In materials such as rocks, wood, most plastics, rubber and glass, there are no—or very few—electrons free to move. These materials reduce or prevent the flow of electricity and are known as insulators. But they may gain or lose electrons on their surface as a static electric charge.

## Uses of electricity

Electricity is one of the most useful forms of energy. It is transportable, which means it can be carried long distances by wires and cables. It is convertible, being changed into many other forms of energy, such as light from an electric light bulb, and movement in an electric motor. It is also controllable. We can turn it on and off with a switch, or up and down with a knob. When a city suffers a power cut and falls still and silent, we realise how much we depend on electricity.

Consultant:
Sharon Ann Holgate