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Unformatted text preview: NORSUZIAN BINTI MOHD ANIM SES060483 FG1 5 & 7 August 2008 HALL EFFECT IN METAL SOLID STATE LAB : SMES 2174 Hall Effect in the Metal OBJECTIVE: 1) To determine the Halls effect in the thin slit sample of zinc and copper 2) To obtain the resistivity and Hall constant for the sample of zinc and copper 3) To obtain mobility electron, for the copper sample INTRODUCTION: In 1879, Hall observed that on placing a current carrying conductor perpendicular to a magnetic field, a voltage is observed perpendicular to both the magnetic field and the current. It was puzzling that the charge carriers, which were assumed to be electrons, experienced a sideways force opposite to what was expected. This was later explained by the band theory of solids. The Hall Effect has been important in the study of the mechanism of conduction in semiconductors because both the mobility and concentration of the charge carriers may be measured, as opposed to only the conductivity with conductivity experiments. THEORY: Assume the conductor to have charge carrier of charge q (can be either positive or negative or both, but we take it to be of just one sign here), charge carrier number density n (i.e., number of carriers per unit volume), and charge carrier drift velocity v x when a current I x flows in the positive x direction. The drift velocity is an average velocity of the charge carriers over the volume of the conductor; each charge carrier may move in a seemingly random way within the conductor, but under the influence of applied fields there will be a net transport of carriers along the length of the conductor. The current I x is the current density J x times the crosssectional area of the conductor WT. The current density J x is the charge density nq times the drift velocity v x . I x = J x WT = nqv x WT (1) The current I x is caused by the application of an electric _eld along the length of the conductor E x . In the case where the current is directly proportional to the _eld, we say that the material obeys Ohm's law, which may be written J x = E x ; (2) where is the conductivity of the material in the conductor. The Hall effect refers to the potential difference (Hall voltage) on the opposite sides of an electrical conductor through which an electric current is flowing, created by a magnetic field applied perpendicular to the current. The Hall effect comes about due to the nature of the current flow in a conductor. Current consists of the movement of many small chargecarrying "particles" (typically, but not necessarily, electrons). Moving charges experience a force, called the Lorentz Force, when a magnetic field is present that is not parallel to their motion. When such a magnetic field is absent, the charges follow an approximately straight, 'line of sight' path. However, when a perpendicular magnetic field is applied, their path is curved so that moving charges accumulate on one face of the material. This leaves equal and opposite charges exposed moving charges accumulate on one face of the material....
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 Spring '10
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