electrical resistivity


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Related to electrical resistivity: Thermal conductivity, Electrical conductivity

Electrical resistivity

The electrical resistance offered by a homogeneous unit cube of material to the flow of a direct current of uniform density between opposite faces of the cube. Also called specific resistance, it is an intrinsic, bulk (not thin-film) property of a material. Resistivity is usually determined by calculation from the measurement of electrical resistance of samples having a known length and uniform cross section according to the following equation, where ρ is the resistivity, R the measured resistance, A the cross-sectional area, and l the length. In the mks system (SI), the unit of resistivity is the ohm-meter. Therefore, in the equation below, resistance is expressed in ohms, and the sample dimensions in meters.

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The room-temperature resistivity of pure metals extends from approximately 1.5 × 10-8 ohm-meter for silver, the best conductor, to 135 × 10-8 ohm-meter for manganese, the poorest pure metallic conductor. Most metallic alloys also fall within the same range. Insulators have resistivities within the approximate range of 108 to 1016 ohm-meters. The resistivity of semiconductor materials, such as silicon and germanium, depends not only on the basic material but to a considerable extent on the type and amount of impurities in the base material. Large variations result from small changes in composition, particularly at very low concentrations of impurities. Values typically range from 10-4 to 105 ohm-meters. See Electrical resistance, Semiconductor

The temperature coefficients (changes with temperature) of resistivity of pure metallic conductors are positive. Resistivity increases by about 0.4%/K at room temperature and is nearly proportional to the absolute temperature over wide temperature ranges. As the temperature is decreased toward absolute zero, resistivity decreases to a very low residual value for some metals. The resistivity of other metals abruptly changes to zero at some temperature above absolute zero, and they become superconductors.

Metals, and some semiconductors in particular, exhibit a change in resistivity when placed in a magnetic field. Theoretical relations to explain the observed phenomena have not been well developed.

electrical resistivity

[i′lek·trə·kəl ‚rē·zis′tiv·əd·ē]
(electricity)
The electrical resistance offered by a material to the flow of current, times the cross-sectional area of current flow and per unit length of current path; the reciprocal of the conductivity. Also known as resistivity; specific resistance.

electrical resistivity, specific resistance

The resistance, in ohms, of an electric conductor of unit cross-sectional area and unit length.
References in periodicals archive ?
The variation of the electrical resistivity with bentonite content for the untreated ultra-soft soil is shown in Figure 7a.
Despite the closer distance of the borehole BH2 than borehole B1 to profile P1, its data was not used for investigating the correlation between electrical resistivity and geotechnical parameters.
Alemayehu, "Electrical resistivity tomography and magnetic surveys: applications for building site characterization at Gubre, Wolkite University site, western Ethiopia," Ethiopian Journal of Science and Technology, vol.
where [mu] is the magnetic permeability of the specimen, [rho] is the radial electrical resistivity of the specimen material looks as the medium value, and d is the diameter of the core sample.
Particularly, the electrodes installed above the groundwater showed very high electrical resistivity depending on the backfilling conditions.
1) and electrical resistivity of the Estonian sedimentary rocks (Joeleht & Kukkonen 2002), RU2, a 15-20 m thick unit with relatively high (>350 [OMEGA]m) resistivity corresponds to Middle Ordovician carbonate rocks.
Therefore, the electrical resistivity of the soil-cement admixture increased.
Figure 6 shows the numerical calculations of FS model using the electrical resistivity values of copper in bulk.
Geophysical techniques study the contrast in the physical properties of the different units in the subsurface such as velocity, electrical resistivity, (conductivity), acoustic properties, subsurface geology and the environmental conditions [8][7][15][18][4] and they can provide some of the information required to delineate those materials in the subsurface space such as the overburden thickness, horizontal and vertical lithologic extents, depth to water table, fault zones [22].
28 days: The addition of 0.1 percent CF to the cement with w/c ratio of 0.38 increased the change in electrical resistivity of oil well cement at failure [([DELTA][rho]/[[rho].sub.0]).sub.f] by 400 percent, as summarized in Table 5.
The electrical resistivity method was selected because the Resistivity meter is available being less costly more portable and the shallow nature of the basement rocks and the water table.
This study involves the determination of harmful heavy metals using electrical resistivity of soil which is a non destructive and comparatively less time consuming method.

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