Electricity

Electricity is the set of phenomena arising from the presence and movement of electric charge. Charge is a fundamental property of matter, carried in everyday situations by electrons and by ions, and it comes in two kinds, conventionally called positive and negative. Like charges repel and unlike charges attract. When charge is held in place it produces static electricity and an electric field; when it flows steadily it constitutes an electric current, which is the basis of most practical uses of electricity.

Three quantities describe a simple circuit. Current is the rate at which charge flows, measured in amperes. Voltage, or potential difference, is the energy given to each unit of charge and is what drives the current; it is measured in volts. Resistance measures how much a material opposes the flow of current, measured in ohms. In many materials these are linked by Ohm's law, which states that the current through a conductor is proportional to the voltage across it and inversely proportional to its resistance.

Electric current comes in two main forms. Direct current (DC) flows steadily in one direction, as from a battery. Alternating current (AC) reverses direction periodically and is used for mains power because its voltage can be raised and lowered efficiently by transformers, allowing energy to be transmitted over long distances. Electrical energy is readily converted into light, heat, motion and sound, which is why electricity underlies lighting, heating, motors and virtually all electronic devices.

Frequently asked questions

What is the difference between current and voltage?

Current is the rate at which electric charge flows, measured in amperes, while voltage is the potential difference that drives that flow, measured in volts.

What does Ohm's law state?

For many materials, the current through a conductor is proportional to the voltage across it and inversely proportional to its resistance.

Why is alternating current used for mains power?

Its voltage can be stepped up and down efficiently by transformers, which allows electrical energy to be transmitted over long distances with low losses.