Conduction Of Electricity
Conduction, the passage of charges in an electrical field, is done by the movement of charged particles in the conducting medium. Good conductors are materials that have available negative or positive charges, like electrons or ions. Semiconductors are less effective in conducting electricity, while most other materials are insulators.
In metals, the atomic nuclei form crystalline structures, where electrons from outer orbits are mobile, or "free." The current (the net transfer of electric charge per unit time) is carried by the free electrons. Yet the transfer of energy is done much faster than the actual movements of the electrons. Among metals at room temperature, silver is the best conductor, followed by copper. Iron is a relatively poor conductor.
In electrolytic solutions, the positive and negative ions of the dissolved salts can carry current. Pure water is a good insulator, and various salts are fair conductors; together, as sea water, they make a good conductor.
Gases are usually good insulators. Yet when they become ionized under the influence of strong electrical fields, they may conduct electricity. Some of the energy is emitted as light photons, with most spectacular effects are seen in lightning.
In semiconductors like germanium and silicon, a limited number of free electrons or holes (positive charges) are available to carry current. Unlike metals, the conductivity of semiconductors increases with temperature, as more electrons are becoming free.
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