(c) Anthony K. Grafton 2003

Shocking Facts About Electricity

Part II: Where does it come from?

There are two “kinds” of electricity: AC and DC. AC stands for alternating current, and it refers to the kind of electricity that powers many common devices that we plug into wall sockets. DC stands for direct current, and it is the kind of electricity that comes from batteries. Each of these two types of electricity is generated in different ways.

Batteries generate electric current through chemical reactions. These electrochemical reactions, which are sometimes called reduction-oxidation reactions, generate electrical current that flows only in one direction, so it is called direct current, or just DC electricity.

In every chemical reaction, some chemical is reducedand some chemical is oxidized. When something is reduced in an electrochemical reaction, it gains electrons, which are the negatively charged, sub-atomic particles found in atoms. The oxidized chemical loses electrons. These electrons moving from the oxidized to the reduced substance form the electric current that can be used to do work.

Alternating current, or AC, electricity is usually generated in a power plant. To generate AC current, a large magnet is turned quickly around a wire or bundle of wires. Any time a magnet moves near a wire, it causes electrical current to flow within the wire. As a magnet is spun around a wire, it causes electricity to flow first in one direction, then back in the other direction. This back and forth movement of the electric current is why we call it alternating current.

To generate AC current, something has to provide the energy to make the magnet turn. This energy can come from falling water in a dam, from burning coal or oil, or from nuclear reactions. However, not all AC generators are found in big power plants. Every car has a part called an alternator, which is just a small AC generator that is turned by a belt connected to the car engine. Cars use this electrical current to power everything from headlights to radios as long as the engine is running. When the engine is not running, then cars draw electrical power from a battery.

Note: Two weeks ago in a Science Corner about Moa and Dodo birds, New Zealand was incorrectly referred to as “an island”. New Zealand is not a single island, but is in fact made up of many islands, the largest of which are Stewart Island, the North Island, and the South Island. Thanks to Margaret for pointing out this mistake. New Zealand has a unique history and ecology, and a future Science Corner will focus on the effect of the country’s geographical isolation on the evolution of its animals and plants.