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In physics, screening is the damping of electric fields caused by the presence of mobile charge carriers. It is an important part of the behavior of charge-carrying fluids, such as ionized gases (classical plasmas), electrolytes, and electronic conductors (semiconductors, metals). In a fluid, with a given relative dielectric constant ''εR'', composed of electrically charged constituent particles, each pair of particles interact through the Coulomb force, :. This interaction complicates the theoretical treatment of the fluid. For example, a naive quantum mechanical calculation of the ground-state energy density yields infinity, which is unreasonable. The difficulty lies in the fact that even though the Coulomb force diminishes with distance as 1/''r''², the average number of particles at each distance ''r'' is proportional to ''r''², assuming the fluid is fairly isotropic. As a result, a charge fluctuation at any one point has non-negligible effects at large distances. In reality, these long-range effects are suppressed by the flow of the fluid particles in response to electric fields. This flow reduces the ''effective'' interaction between particles to a short-range "screened" Coulomb interaction. For example, consider a fluid composed of electrons in a background of positive charge. Each electron possesses a negative charge. According to Coulomb's interaction, negative charges repel each other. Consequently, this electron will repel other electrons creating a small region around itself in which there are fewer electrons. This region can be treated as a positively charged "screening hole". Viewed from a large distance, this screening hole has the effect of an overlaid positive charge which cancels the electric field produced by the electron. Only at short distances, inside the hole region, can the electron's field be detected. == Electrostatic screening == The first theoretical treatment of screening, due to Debye and Hückel,〔 (- e\Delta\rho(r) ). To proceed, we must find a second independent equation relating ''Δρ'' and ''Δφ''. We consider two possible approximations, under which the two quantities are proportional: the Debye-Hückel approximation, valid at high temperatures, and the Fermi-Thomas approximation, valid at low temperatures. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Electric-field screening」の詳細全文を読む スポンサード リンク
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