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Topic: Resistivity

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	The T.W.I.N.K.I.E.S. Resistivity Test
		To test the resistivity of a Twinkie, a 110V standard AC household current was run across it.
		After verifying that power was being supplied to the Twinkie, we concluded that the resistivity of the Twinkie must be so high that not enough current was passing through to cause any noticeable change.
		A quick measurement with a Digital Multimeter (DMM) confirmed that the resistivity was beyond the DMM's range.
	www.twinkiesproject.com /resistivity.html (0 words)

	Resistance
		The resistance to the flow of charge in an electric circuit is analogous to the frictional effects between water and the pipe surfaces as well as the resistance offered by obstacles which are present in its path.
		A third variable which is known to effect the resistance to charge flow is the material that a wire is made of.
		Consistent with the discussion above, this equation shows that the resistance of a wire is directly proportional to the length of the wire and inversely proportional to the cross-sectional area of the wire.
	www.glenbrook.k12.il.us /gbssci/phys/class/circuits/u9l3b.html (912 words)

	Resistivity - Wikipedia, the free encyclopedia
		The SI unit of electrical resistivity is the ohm metre.
		In general, electrical resistivity of metals increases with temperature, while the resistivity of semiconductors decreases with increasing temperature.
		The resistivity of semiconductors depends strongly on the presence of impurities in the material.
	en.wikipedia.org /wiki/Resistivity (615 words)

	Resistivity
		It is a measure of the resistance to the flow of current from a microscopic level, that is, as explained in terms of the atoms, the basic building blocks of all solid materials.
		In the discussion of resistance, we stated that resistance varies directly with the length L and indirectly with the uniform cross-sectional area A of a conductor.
		Summarizing, the resistance R of an electrical circuit is a function of the shape, size, and nature of a solid material.
	mst-online.nsu.edu /mst/electronic/electronic2.htm (679 words)

	Resistivity
		The resistivity of soils is a complicated function of porosity, permeability, ionic content of the pore fluids, and clay mineralization.
		The apparent resistivity is the bulk average resistivity of all soils and rock influencing the flow of current.
		In resistivity soundings, the distance between the current electrodes or the distance between the current and potential dipoles is expanded in a regular manner between readings, thus yielding information of the electrical properties of soils from deeper and deeper depths.
	www.baygeo.com /html/resistivity.html (262 words)

	Applications of the Electrical Resistivity Method for Detection of Underground Mine Workings - Geotechnical Hazards ... (Site not responding. Last check: )
		Resistivity of a material is a fundamental physical property related to the ability of a material to conduct electricity.
		Resistivity measurements of the ground are normally made by injecting current through two current electrodes and measuring the resulting voltage difference at two potential electrodes.
		The mine is assumed to be flooded with water of a resistivity of 20 ohm-meters and the coal is assumed to have a resistivity of 1,000 ohm-meters.
	www.fhwa.dot.gov /engineering/geotech/hazards/mine/workshops/ktwkshp/ky0311.cfm (3808 words)

	Resistance and Resistivity
		The electrical resistance of a circuit component or device is defined as the ratio of the voltage applied to the electric current whichflows through it:
		The electrical resistance of a wire would be expected to be greater for a longer wire, less for a wire of larger cross sectional area, and would be expected to depend upon the material out of which the wire is made.
		The electrical resistance of a wire would be expected to be greater for a longer wire, less for a wire of larger cross sectional area, and would be expected to depend upon the material out of which the wire is made (resistivity).
	230nsc1.phy-astr.gsu.edu /hbase/electric/resis.html (422 words)

	Copper and electricity. Resistance and resisitivty.
		In effect, the resistivity represents the resistance across two opposite faces of a cubic metre of material (in the same way that density is the mass of a cubic metre).
		The smaller the resistivity, the better the material is at conducting electricity.
		Resistivity is the inverse of conductivity (which tells us how good a conductor a material is).
	www.schoolscience.co.uk /content/5/physics/copper/copelech2pg1.html (405 words)

	Environmental Geophysics Methods: DC Resistivity Dr Ruppel (Site not responding. Last check: )
		The DC resistivity method relies on the application of Ohm'’s Law V=-IR (V is potential difference, I gives current, and R denotes resistance) to constrain the composition, structure, and/or hydrology of the subsurface.
		Resistance R is a property of the path that current follows through a material and depends on the length L of the path followed by the current.
		DC resistivity surveys are usually conducted by electrifying 2 electrodes and measuring the potential across another pair of electrodes.
	hydrate.eas.gatech.edu /sapelo/methods.dir/dcresistivity.html (1413 words)

	Resistivity Methods (Site not responding. Last check: )
		Surface electrical resistivity surveying is based on the principle that the distribution of electrical potential in the ground around a current-carrying electrode depends on the electrical resistivities and distribution of the surrounding soils and rocks.
		Apparent resistivity is defined as the resistivity of an electrically homogeneous and isotropic half-space that would yield the measured relationship between the applied current and the potential difference for a particular arrangement and spacing of electrodes.
		Resistivity surveys are made to satisfy the needs of two distinctly different kinds of interpretation problems: (1) the variation of resistivity with depth, reflecting more or less horizontal stratification of earth materials; and (2) lateral variations in resistivity that may indicate soil lenses, isolated ore bodies, faults, or cavities.
	www.freewebtown.com /geophysics2/elec3.html (7138 words)

	Electrical resistivity at opensource encyclopedia (Site not responding. Last check: )
		Electrical resistivity (also known as specific electrical resistance) is a measure indicating how strongly a material opposes the flow of electric current; if the resistivity of the material is small, that means that material is effective to carry electrons.
		The resistivity of a material is usually denoted by the lower-case Greek letter rho (ρ) and is given by RS/l, where R is the resistance of a uniform specimen of the material, having a length l and a cross-section area S.
		Also the resistivity is the magnitude of the electric field divided by the magnitude of the current density.
	www.wiki.tatet.com /Electrical_resistivity.html (221 words)

	Electrical Resistivity Imaging
		DC resistivity techniques, sometimes referred to as electrical resistivity, electrical resistivity imaging or vertical electric sounding, measure earth resistivity by driving a direct current (DC) signal into the ground and measuring the resulting potentials (voltages) created in the earth.
		The apparent resistivity is the resistivity of the homogeneous half-space which would produce the observed instrument response for a given electrode spacing.
		Resistivity models are generally not unique; i.e., a large number of earth models can produce the same observed data or sounding curve.
	www.nga.com /Geo_ser_DC_tech.htm (485 words)

	Volume Resistivity - BetaTHERM Sensors Temperature Solutions
		Resistivity is specified in units of resistance (ohms) multiplied by units of length (usually cm).
		Resistance is proportional to thickness (length of current path) because for a uniform cross-sectional area, increasing the thickness of a conductor is similar to combining resistors in series.
		Likewise, the resistance is inversely proportional to the cross-sectional area as increasing the cross-sectional area is similar to combining resistors in parallel, which reduces the overall resistance.
	www.betatherm.com /volumeresist.htm (719 words)

	Resistance and Resistivity
		The electrical resistance of a circuit component or device is defined as the ratio of the voltage applied to the electric current whichflows through it:
		The electrical resistance of a wire would be expected to be greater for a longer wire, less for a wire of larger cross sectional area, and would be expected to depend upon the material out of which the wire is made.
		The electrical resistance of a wire would be expected to be greater for a longer wire, less for a wire of larger cross sectional area, and would be expected to depend upon the material out of which the wire is made (resistivity).
	hyperphysics.phy-astr.gsu.edu /hbase/electric/resis.html (422 words)

	Resistivity of Iron
		Electrical resistivity is a property of any object or substance to resist or oppose the flow of an electrical current.
		The resistivity of a material is usually represented by the lower-case Greek letter rho (ρ;) and is derived from the formula RA / l, where R is the resistance of a uniform specimen of the material, having a length l and a cross-sectional area A.
		Resistivity is most commonly tested at a temperature of 20 °C. At this temperature, the resistivity of iron is approximately 100 nΩ·m.
	hypertextbook.com /facts/2004/JonathanRuditser.shtml (310 words)

	Cyberphysics - resistivity (Site not responding. Last check: )
		Resistance depends on the material the wire is made of
		R is the resistance of the wire (the ratio of the potential difference across its end to the current that flows through it)
		The electrical resistivity, or specific resistance, is the resistance between the opposite faces of a metre cube of a material.
	www.cyberphysics.pwp.blueyonder.co.uk /topics/physics/electric/resistance/resistivity.htm (403 words)

	Resistivity
		Resistivity is the property of a material that resists the flow of electrical current.
		A resistivity survey is an example of active geophysical method because this method requirements the injection of an electric current into the ground through electrodes and it measures the resistivity (response) of the ground in the subsurface.
		A resistivity survey can produce detailed pseudosection of the subsurface which can be used as a measure of the depth to the apparent resistivity.
	www.globalgeo.co.za /resis.htm (236 words)

	Measurement of Electrical Conductivity of Glass Melts
		For accurate measurements of the electrical resistivity of glass melts several details have to be considered: At the beginning of measurements, relatively low potential barriers occur for some conducting ions due to a broad potential barrier distribution based on polarization effects in the electric field ("ionic polarization").
		For obtaining resistivity data with reduced or negligible influence of electrode polarization effects, it is beneficial to record the electrical resistivity over various frequencies and to extrapolate to a constant resistivity value in the frequency-independent region.
		The applied voltage during resistivity measurements of glass melts is not reported in several papers unfortunately, despite its influence on the resistivity at high voltages due to various ionization potentials of the conducting ions [10, 11].
	glassproperties.com /resistivity/ElectrResistMeasurement.htm (1851 words)

	It's Resistivity, not Resistance (Site not responding. Last check: )
		The problem with using resistance as a measurement is that it depends not only on the material out of which the wire is made, but also the geometry of the wire.
		In the case of the wire, resistivity is defined as the resistance in the wire, multiplied by the cross-sectional area of the wire, divided by the length of the wire.
		Resistivity is a fundamental parameter of the material making up the wire that describes how easily the wire can transmit an electrical current.
	www.earthsci.unimelb.edu.au /ES304/MODULES/RES/NOTES/resistivity.html (319 words)

	Resistivity
		Because resistivity values for most metals are already well established, you can use the NDT Automation M100A Metal Inspector to rapidly identify a metal through its resistivity “value”.
		The nondestructive resistivity testing technique can be used to determine the uniformity of filler materials and helps detect areas where voids may exist.
		using resistivity to quickly and accurately measure the thickness of conductive coatings sprayed on metal to metal and metal to non-metal surfaces.
	www.envirocoustics.gr /products/resistivity/resistivity_eng.htm (510 words)

	Resistivity - 3D Explorer - Petrophysical Analysis (Site not responding. Last check: )
		Resistivity measurements that investigate deeply into the formation are therefore needed to accurately resolve formation parameters associated with the undisturbed formation beyond the depth of invasion.
		With resistivity measurements, the necessity for deep depth of investigation tends to preclude fine vertical resolution.
		The horizontal resistivity is dominated by the shale conductivity, which makes it difficult to quantify the saturation of the sand laminae in the low resistivity pay sections.
	www.bakerhughes.com /BakerAtlas/formation_evaluation/3dexplorer_petroanalysis.htm (450 words)

	Electrical resistivity - Wikipedia, the free encyclopedia (Site not responding. Last check: )
		Finally, electrical resistivity is also defined as the inverse of the conductivity of the metal, or:
		The electric resistivity of a typical semiconductor decreases exponentially with the temperature.
		An even better approximation of the temperature dependence of the resistivity of a semiconductor is given by the equation:
	www.ci.temecula.us /project/wikipedia/index.php/Electrical_resistivity (382 words)

	Electrical Resistivity (Site not responding. Last check: )
		At small spacing between electrodes, apparent resistivity is close to the resistivity of the upper layer.
		If the middle layer has a higher or lower resistivity than the other two layers, it can be seen with an expanding spread survey where apparent resistivity will increase and then decrease or vice versa.
		Reversals in apparent resistivity are caused by changes in the current distribution as the electrodes are moved.
	www.geol.lsu.edu /Faculty/Nunn/4002_1/chp5.html (662 words)

	J R Associates- Resistivity Methods
		Resistivity techniques are used to analyze soils for electrical grounding grids.
		The size of a grounding grid is in part dependent on the electrical resistivity of the soil.
		The average resistivity to a depth equal to the "a" spacing is calculated from the voltage, current and "a" spacing.
	www.greatgeophysics.com /resis.htm (294 words)

	Earth Dynamics: Electrical Resistivity
		The properties that affect the resistivity of soil or rock include: porosity, water content, composition (clay mineral and metal content), salinity of the pore water, and grain size distribution.
		In an electrical resistivity exploration, electrical current is applied to the ground surface through two electrodes.
		resistivity exploration: 1) electrical traversing in which the electrode separation remains constant during the survey; and 2) electrical sounding, in which the center of the electrode spread is maintained at a fixed location and the electrode spacing is increased in increments.
	www.earthdyn.com /resist.html (358 words)

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