Static electricity Current electricity Voltage and current - what's the difference? Electrical flow Starting and stopping the flow

Electrical energy is a form of potential energy. It comes about from the attraction and repulsion of electrically charged particles. When two charged particles come near each other, their action on each other will either make them move apart or move together. In each case, electrical potential energy is transformed to kinetic energy of the moving particles.

The word electricity comes from a Greek word elektron. Electrical energy is all to do with electrons and protons, parts of all atoms, the basic building blocks of our Universe. Atoms are made up of a dense positively charged nucleus in the centre, surrounded by clouds of negatively charged particles called electrons. These electrons are arranged in clouds and it is the outermost electrons, or valence electrons, that are involved in electrical effects.

These electrons, moving around the outermost parts of the atom are sometimes easily removed - especially from metal atoms. In metals, these electrons are shared by all the atoms in the structure and it is the movement of these electrons through the metal that produces an electric current.

Materials that allow easy movement of electrons are called electrical conductors, while those that don't allow electron flow are called electrical insulators. Good conductors are metals and some non-metals, such as carbon or graphite. Insulators tend to be plastics, ceramics, glass and a few non-metal solid elements.

Static electricity
You might have experienced the effects of static electricity when you walked across a synthetic carpet, then touched a metal object, or when you removed one piece of clothing from another made from a different material and experienced an electric shock. Static electricity is caused by charge separation or transfer. When you walk across a carpet, electrons may transfer from the soles of your shoes to the carpet or vice versa. This leaves your shoes, and yourself, with a net charge and the carpet with the opposite charge. When you then touch a conductor, like a door knob, the excess charge on your body discharges through the doorknob; this is the electric shock. It's called static electricity because, until the charge is transferred, the charge builds up but does not move in a directional current.

Current electricity
Current electricity is the most common form, and is more useful to us. In this case electrons flow around a circuit and carry electrical energy that is transformed into other forms of energy in the circuit. Your computer uses current electricity, usually coming from the mains supply, but sometimes from a stored source, like batteries. The focus of the rest of this topic is on current electricity.

Voltage and current - what's the difference?
Current is a flow of charge through a conductor. The carriers of electrical energy are the electrons, but electricians and physicists talk about current as the movement of positive charge. In atoms, the positive charge is on protons and they cannot move through a wire because they are firmly held in place in the nucleus of the atoms. Hence, positive charge cannot move, only electrons move. This is a historical hangover from the first definition of current. Confused? Don't be - electrons carry the electrical energy in a current.

Voltage can be thought of as the ability to cause current to flow in a conductor. It is a measure of electrical potential energy change. The greater the voltage, (or potential difference as it is often called) the greater the current in a circuit. For example, a 12 volt battery will cause twice as great a current to flow around a circuit as a 6 volt battery.

An everyday example of this concept is turning on a tap above a sink. Due to its height above the sink, water can flow, but does not actually flow until the tap is opened. Voltage is like the tap water pressure, current is like the rate of flow of water, and the tap is like an electrical switch.

Electrical flow
As electrons flow through a circuit their electrical potential energy is transformed into other forms of energy. In an electric light globe the electrical potential energy is transformed into light and thermal energy; an electric motor transforms electrical potential energy into kinetic energy; a radiant heater produces thermal energy and your radio converts electrical potential energy into sound energy. Electricity is an important power source in our modern society - how does it work?

Think of an ordinary battery (a single unit is really called a cell but we'll use the common word). One end has a bit sticking out and this is called the positive terminal, the other end is the negative terminal.

A battery is a chemical factory that stores chemical potential energy. When a current flows in a circuit, due to the presence of the battery this energy is transferred by electrons as electrical potential energy. It then flows through the circuit, being transformed to other forms of energy such as thermal, kinetic, sound and light energy.

The supply of chemical potential energy is limited so its ability to cause a current to flow is also limited. Eventually the battery will exhaust its usable chemical energy supply and the battery is said to "lose charge" or "go flat". An important point to realise here is that batteries do not "create electrons", they simply transform chemical potential energy into electrical potential energy. Rechargeable batteries are able to store chemical potential energy from electrical potential energy in the mains supply - this type of battery is convenient because it is portable and replaceable.

Starting and stopping the flow
To allow electrons to flow a complete circuit is needed. Usually wires covered with plastic connect one terminal of the battery to the other through various components and back to the other terminal of the battery.

A simple device to produce light is a torch where one or more batteries are connected through a metal circuit and a globe. The globe has a high resistance filament in which energy is transformed to thermal energy and light energy.

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