Volume specific resistance

The bulk (or volume)-specific resistance is one of the most useful general electrical properties. Specific resistance is a physical quantity that may vary more than 10 in readily available materials. This unusually wide range of conductivity allows wide variety of electrical applications. Conductive materials, such as copper, have specific resistance values of about 10 fl-cm, whereas good insulators such as polytetrafluoroethylene and LDPE have values of about 10 fl-cm. Specific resistance is calculated from the following equation where R is the resistance in ohms, a is the pellet area in square centimeters, t is the pellet thickness in centimeter, and P is the specific resistance in ohm-centimeter ... 

Polysulfonamide (PSA) fiber is a special high-performance fiber developed in China. It is a new FR fiber with excellent heat resistance, thermal stability and thermal oxidation, high volume specific resistance and initial modulus, instability of crimp, and low friction coefficient. The main physical properties of PSA are listed in Table 2.59. PSA fiber usually has a round shape (Fig. 2.22). 

Volume resistivity or specific resistance this is the resistance of a conductor of unit length and unit cross-sectional area. i.e. 

Backfill containing a large proportion of bentonite has a tendency to change its volume with variations in water content of the surrounding soil. This can lead to formation of hollow cavities in the backfill with a considerable decrease in the current delivery. A standard backfill consists of a mixture of 75% gypsum, 20% bentonite and 5% sodium sulfate. The specific resistivity of this backfill is initially 0.5 to 0.6 m and can rise with increased leaching to 1.5 m. 

Volume resistivity Or specific resistivity of a material, expressed in W/cm. Resistance to electrical current flow through the bulk of an object. 

These test procedures and standards are subject to change, so it is essential to keep up to date if one has to comply with them. It may be possible to obtain the latest issue on a specific test (such as a simple tensile test or a molecular weight test) by contacting the organization that issued it. For example, the ASTM issues new annual standards that include all changes. Their Annual Books of ASTM Standards contain more than seven thousand standards published in sixty-six volumes that include different materials and products. There are four volumes specifically on plastics 08.01-Plastics 1 08.02-Plastics 11 08.03-Plastics III, and 08.04-Plastic Pipe and Building Products. Other volumes include information on plastics and RPs. The complete ASTM index are listed under different categories for the different products, types of tests (by environment, chemical resistance, etc.), statistical analyses of different test data, and so on (56,128,129). 

Specific resistance. See Surface Resistivity and Volume Resistivity. 

If the volume of filtrate is measured as a function of time, under constant pressure, then a plot of t/V against V should give a straight line, the slope of which can be used to calculate the specific resistance. 

Generally, the absolute magnitude of Q is not as important as the ratio leak rate to the total flow rate Qieaf/QtotJ. The leakage rate given by Equation (5.4) is the volume flow rate at the temperature and pressure of the leakage flow, and must be corrected to standard conditions for comparison with reactant feed rates. The total required flow rate of fuel or air to the stack is proportional to the stack current, which increases with the electrochemically active area and is inversely proportional to the cell area specific resistance (R"). 

Faraday s constant (96,487 C/mol) overpotential total current current density exchange current density ratio of ohmic constriction to inter-facial resistance surface exchange coefficient volume-specific interfacial resistance in a composite thickness utilization length characteristic length of a porous microstructure... 

Many of the applications for composite materials involve their (relative) lightweight, resistance to weathering and chemicals, and their ability to be easily fabricated and machined. Bulk applications employ composites that are relatively inexpensive. Combinations of rigorous specifications, low volume, specific machining and fabrication specifications, and comparative price to alternative materials and solutions allow more expensive specialized composites to be developed and utilized. 

Because the surface of rubbers may conduct electricity more easily than the bulk of the material, it is usual to distinguish between volume resistivity and surface resistivity. Volume resistivity is defined as the electrical resistance between opposite faces of a unit cube, whereas surface resistivity is defined as the resistance between opposite sides of a square on the surface. Resistivity is occasionally called specific resistance. Insulation resistance is the resistance measured between any two particular electrodes on or in the rubber and, hence, is a function of both surface and volume resistivities and of the test piece geometry. Conductance and conductivity are simply the reciprocals of resistance and resistivity respectively. 

Specific volume electric resistance of varnish film, Ohm cm, at least 4-1014 MO14 MO14 4-1013... 

Specific volume electric resistance, Ohm cm 1.8T014 1.9T014... 

In this case the losses in voltage due to the resistance of the electrolyte cannot be calculated by the usual method i. e. from the specific resistance of the solution, the spacing of the electrodes and the area of their surfaces this difficulty is caused by the presence of gas bubbles suspended in the solution these bubbles decrease the actiial cross section between the electrodes, i. e. the area covered by the lines of force, and consequently the resistance of the bath rises. The decrease of conductance of the electrolyte caused by suspended bubbles is more marked when the current is higher, the height of electrodes greater (as bubbles accumulate mainly at the upper end of the electrode), the electrolytic cell narrower and the movement of the electrolyte slower. The amount of bubbles in one unit of volume also depends on the viscosity and the temperature of the electrolyte. 

As already mentioned the resistance of the electrolyte does not only depenc on the specific resistance, the spacing and the surface of the electrodes, but also on the ratio of the volume of gas bubbles to the total volume of the electrolyte. The influence of bubbles upon conductance is considerable for instance if the volume of bubbles in the electrolyte equals 35 per cent, resistance is twice that of an electrolyte without bubbles. If hubbies are present in the electrolyte the summary resistance across the electrolyte cannot be decreased by bringing the anode closer to the cathode, because the effect of the gas accumulated in this... 

Properties of substances, undergoing structural phase transitions at pressure P, are a complex functions of the extent of transformation [1], In the region of the phase transformation the sample of volume V appear to be a mixture of phases with the concentrations c, = Vi/V, where Vj - is the volume of i-phase (5Z K = F). In effective medium approximation the value of specific resistivity p of such mixture may be written as a normalized sum of the phases contributions [2]... 

The thermal effects caused by short-circuits can be calculated as follows the overtemperature AT of a conductor of length l, resistance R, cross-sectional area A and volume V, made of material with density cr and mass m, specific heat c and specific resistance p, caused by the current /(t), and without any heat dissipation to the environment, reads ... 

Mercury has a high density (13.546 g cm" at 20 °C) and a wide liquid range (mp -38.9 °C bp 357) over most of which its volume expands uniformly. In addition, the high surface tension of mercury keeps it from sticking to glass surfaces. These properties have contributed to its use in an impressive number of laboratory applications. For a metal, mercury has an unusually high electrical resistivity or specific resistance (95.8 J,S2 cm), and this property enables it to be used as an electrical standard. Of all the common metals, only bismuth has a higher resistivity. 

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