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How Electric Current Is Conducted

gas atoms, Liquid Solutions, free electrons, positive point, positive ions

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>  Conduction in Solids

All electric currents consist of charges in motion. However, electric current is conducted differently in solids, gases, and liquids. When an electric current flows in a solid conductor, the flow is in one direction only, because the current is carried entirely by electrons. In liquids and gases, however, a two-directional flow is made possible by the process of ionization.

Conduction in Gases

Gases normally contain few free electrons and are generally insulators. When a strong potential difference is applied between two points inside a container filled with a gas, the few free electrons are accelerated by the potential difference and collide with the atoms of the gas, knocking free more electrons. The gas atoms become positively charged ions and the gas is said to be ionized. The electrons move toward the high-potential (more positive) point, while the ions move toward the low-potential (more negative) point. An electric current in a gas is composed of these opposite flows of charges.

Conduction in Liquid Solutions

Many substances become ionized when they dissolve in water or in some other liquid. An example is ordinary table salt, sodium chloride (NaCl). When sodium chloride dissolves in water, it separates into positive sodium ions, Na+, and negative chlorine ions, Cl-. If two points in the solution are at different potentials, the negative ions drift toward the positive point, while the positive ions drift toward the negative point. As in gases, the electric current is composed of these flows of opposite charges. Thus, while water that is absolutely pure is an insulator, water that contains even a slight impurity of an ionized substance is a conductor.

Since the positive and negative ions of a dissolved substance migrate to different points when an electric current flows, the substance is gradually separated into two parts. This separation is called electrolysis.

Article key phrases:

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