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The drift velocity is the flow velocity that a particle, such as an electron, attains due to an electric field. It can also be referred to as axial drift velocity. In general, an electron will propagate randomly in a conductor at the Fermi velocity. An applied electric field will give this random motion a small net flow velocity in one direction. In a semiconductor, the two main carrier scattering mechanisms are ionized impurity scattering and lattice scattering. Because current is proportional to drift velocity, which in a resistive material is, in turn, proportional to the magnitude of an external electric field, Ohm's law can be explained in terms of drift velocity. The most elementary expression of Ohm's law is: : where is the drift velocity, is the electron mobility (with units m2/(V⋅s)) of the material and is the electric field (with units V/m). ==Experimental measure== The formula for evaluating the drift velocity of charge carriers in a material of constant cross-sectional area is given by: : where is the drift velocity of electrons, is the current density flowing through the material, is the charge-carrier number density, and is the charge on the charge-carrier. In terms of the basic properties of the right-cylindrical current-carrying metallic ohmic conductor, where the charge-carriers are electrons, this expression can be rewritten as : : where * is again the drift velocity of the electrons, in m⋅s−1 * is the molecular mass of the metal, in kg * is the voltage applied across the conductor, in V * is the density (mass per unit volume) of the conductor, in kg⋅m−3 * is the elementary charge, in C * is the number of free electrons per atom * is the length of the conductor, in m * is the electric conductivity of the medium at the temperature considered, in S/m. 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「Drift velocity」の詳細全文を読む スポンサード リンク
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