what is specific resistivity?

Answer 1

Specific resistance, or resistivity, is the resistance in ohms offered by a unit volume (the circular-mil- foot or the centimeter cube) of a substance to the flow of electric current. Resistivity is the reciprocal of conductivity. A substance that has a high resistivity will have a low conductivity, and vice versa. Thus, the specific resistance of a substance is the resistance of a unit volume of that substance. Many tables of specific resistance are based on the resistance in ohms of a volume of a substance 1 foot in length and 1 circular mil in cross-sectional area. The temperature at which the resistance measurement is made is also specified. If you know the kind of metal a conductor is made of, you can obtain the specific resistance of the metal from a table.

The electrical resistivity ρ (rho) of a material is usually defined by the following:

ρ=R*A/l

where

ρ is the static resistivity (measured in ohm metres)
R is the electrical resistance of a uniform specimen of the material (measured in ohms)
l is the length of the specimen (measured in metres)
A is the cross-sectional area of the specimen (measured in square metres)
Electrical resistivity can also be defined as:
ρ=E/J

where

E is the magnitude of the electric field (measured in volts per metre)
J is the magnitude of the current density (measured in amperes per square metre)

Answer 2

Specific Resistance

Answer 3

Electrical resistivity (also known as resistivity, specific electrical resistance, or volume resistivity) is an intrinsic property that quantifies how strongly a given material opposes the flow of electric current. A low resistivity indicates a material that readily allows the movement of electric charge. Resistivity is commonly represented by the Greek letter ρ (rho). The SI unit of electrical resistivity is the ohm⋅metre (Ω⋅m)[1][2][3] although other units like ohm⋅centimetre (Ω⋅cm) are also in use. As an example, if a 1 m × 1 m × 1 m solid cube of material has sheet contacts on two opposite faces, and the resistance between these contacts is 1 Ω, then the resistivity of the material is 1 Ω⋅m.

Electrical conductivity or specific conductance is the reciprocal of electrical resistivity, and measures a material's ability to conduct an electric current. It is commonly represented by the Greek letter σ (sigma), but κ (kappa) (especially in electrical engineering) or γ (gamma) are also occasionally used. Its SI unit is siemens per metre (S/m) and CGSE unit is reciprocal second (s−1).
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Answer 4

1-1.—Specific Resistances of Common Substances Specific resistance at 20ºC. Substance Centimeter cube (microhoms) Copper (drawn) 1.724

Answer 5

As long as the current density is totally uniform in the conductor, the DC resistance R of a conductor of regular cross section can be computed as

R= l ρ/A

where

L is the length of the conductor, measured in meters
A is the cross-sectional area, measured in square meters
ρ (Greek: rho) is the electrical resistivity (also called specific electrical resistance) of the material, measured in ohm · meter. Resistivity is a measure of the material's ability to oppose the flow of electric current.
For practical reasons, almost any connections to a real conductor will almost certainly mean the current density is not totally uniform. However, this formula still provides a good approximation for long thin conductors such as wires.



Electrical resistivity (also known as specific electrical resistance) is a measure of how strongly a material opposes the flow of electric current. A low resistivity indicates a material that readily allows the movement of electrical charge. The SI unit of electrical resistivity is the ohm metre.

The electrical resistivity ρ (rho) of a material is usually defined by the following:
ρ= RA/l

where

ρ is the static resistivity (measured in ohm metres)
R is the electrical resistance of a uniform specimen of the material (measured in ohms)
l is the length of the specimen (measured in metres)
A is the cross-sectional area of the specimen (measured in square metres)
Electrical resistivity can also be defined as:
ρ= E/J
where

E is the magnitude of the electric field (measured in volts per metre)
J is the magnitude of the current density (measured in amperes per square metre)
Finally, electrical resistivity is also defined as the inverse of the conductivity σ (sigma), of the material, or:

ρ= 1/sigma

In general, electrical resistivity of metals increases with temperature, while the resistivity of semiconductors decreases with increasing temperature. In both cases, electron-phonon interactions can play a key role. At high temperatures, the resistance of a metal increases linearly with temperature. As the temperature of a metal is reduced, the temperature dependence of resistivity follows a power law function of temperature

As the temperature of the metal is sufficiently reduced (so as to 'freeze' all the phonons), the resistivity usually reaches a constant value, known as the residual resistivity. This value depends not only on the type of metal, but on its purity and thermal history. The value of the residual resistivity of a metal is decided by its impurity concentration. Some materials lose all electrical resistivity at sufficiently low temperatures, due to an effect known as superconductivity.

When analysing the response of materials to alternating electric fields, as is done in certain types of tomography, it is necessary to replace resistivity with a complex quantity called impedivity, in analogy to impedance. Impedivity is the sum of a real component, the resistivity, and an imaginary component, the reactivity (reactance) [1].

Answer 6

specific resistivity is defined as resistance of material having unit length and unit area of cross section
it means that resistance of a conductor is directly proportional to length and inversely proportional to area of area of cross section of the conductor
units ohm-cm or ohm-m

Answer 7

Resistivity of a material is the resistance of wire of that material of unit are of cross section and unit length. Its SI unit is ohm/m.

Answer 8

Definition

The electrical resistivity, or specific resistance, ρ, is the resistance between the opposite faces of a metre cube of a material.
Units

10-8 Ohm m
Notes

Values are quoted at 293-298 K and are given in the SI units of Ohm m. Values are often quoted in micro ohm cm and to convert to these units, multiply by 100 000 000. Most numbers are probably reasonably accurate to 2 significant figures where quoted but it is clear that you should expect values to depend upon your particular sample.

Values are affected by impurities. Values given in different sources vary considerably. Those given here are an average if there is no great consensus. Resistivity is temperature dependent. See the references for values at other temperatures. In some cases, resistivity depends upon in which direction along a single crystal the measurement is made.

The reciprocal of the electrical resistivity is the electrical conductivity.



Electrical resistivity (also known as specific electrical resistance) is a measure of how strongly a material opposes the flow of electric current. A low resistivity indicates a material that readily allows the movement of electrical charge. The SI unit of electrical resistivity is the ohm metre.

Temperature dependence

In general, electrical resistivity of metals increases with temperature, while the resistivity of semiconductors decreases with increasing temperature. In both cases, electron-phonon interactions can play a key role. At high temperatures, the resistance of a metal increases linearly with temperature. As the temperature of a metal is reduced, the temperature dependence of resistivity follows a power law function of temperature. Mathematically the temperature dependence of the resistivity ρ of a metal is given by the Bloch-Gruneissen formula :

\rho(T)=\rho(0)+A(\frac{T}{\Theta_R})^n\int_0^{\frac{\Theta_R}{T}}\frac{x^n}{(e^x-1)(1-e^{-x})}dx

where ρ(0) is the residual resistance due to defect scattering, A is a constant that depends on the velocity of electrons at the fermi surface, the Debye radius and the number density of electrons in the metal. ΘR is the Debye temperature as obtained from resistivity measurements and matches very closely with the values of Debye temperature obtained from specific heat measurements. n is an integer that depends upon the nature of interaction:

1. n=5 implies that the resistance is due to scattering of electrons by phonons (as it is for simple metals)
2. n=3 implies that the resistance is due to s-d electron scattering (as is the case for transition metals)
3. n=2 implies that the resistance is due to electron-electron interaction.

As the temperature of the metal is sufficiently reduced (so as to 'freeze' all the phonons), the resistivity usually reaches a constant value, known as the residual resistivity. This value depends not only on the type of metal, but on its purity and thermal history. The value of the residual resistivity of a metal is decided by its impurity concentration. Some materials lose all electrical resistivity at sufficiently low temperatures, due to an effect known as superconductivity.

An even better approximation of the temperature dependence of the resistivity of a semiconductor is given by the Steinhart-Hart equation:

1/T = A + B \ln(\rho) + C (\ln(\rho))^3 \,

where A, B and C are the so-called Steinhart-Hart coefficients.

This equation is used to calibrate thermistors.

[edit] Complex resistivity

When analysing the response of materials to alternating electric fields, as is done in certain types of tomography, it is necessary to replace resistivity with a complex quantity called impedivity, in analogy to impedance. Impedivity is the sum of a real component, the resistivity, and an imaginary component, the reactivity (reactance)

Answer 9

resistivity
n : a material's opposition to the flow of electric current; measured in ohms [syn: electric resistance, electrical resistance, impedance, resistance, ohmic resistance]

Answer 10

specific resistivity(s)=RA/l
DEF:resistance of conductor is one ohm contains unit area of crosssection having one meter length