electricity

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All phenomena caused by electric charge. There are two types of electricity: static and current. Electric charge is caused by an excess or deficit of electrons in a substance, and an electric current is the movement of charge through a material. Materials having equal numbers of positive and negative charges are termed neutral, as the charges balance out. Substances may be electrical conductors, such as metals, which allow the passage of electricity through them readily, or insulators, such as rubber, which are extremely poor conductors. Substances with relatively poor conductivities that increase with a rise in temperature or when light falls on the material are known as semiconductors. Electric currents also flow through the nerves of organisms. For example, the optic nerve in humans carries electric signals from the eye to the brain. Electricity cannot be seen, but the effects it produces can be clearly seen; for example, a flash of lightning, or the small sparks produced by rubbing a nylon garment.

Electricity is essential to modern society. Electrical devices are used in the home, office, and industry, powered by mains electricity. The energy provided by the mains supply is measured in kilowatt hours. Electrical energy is used to power devices used for communications such as fax machines, telephones, computers, and satellites.

Nordic flags bearing the Scandinavian cross are based on the Danish flag, known as the Dannebrog, ‘Danish cloth’. Effective date: 1 May 1893. >>