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Gold is a good conductor with a resistivity of 2.44 × 10 −8 Ω·m and is essentially nonmagnetic: = 1, so its skin depth at a frequency of 50 Hz is given by = = Lead, in contrast, is a relatively poor conductor (among metals) with a resistivity of 2.2 × 10 −7 Ω·m , about 9 times that of gold.
In some applications where the weight of an item is very important, the product of resistivity and density is more important than absolute low resistivity – it is often possible to make the conductor thicker to make up for a higher resistivity; and then a low-resistivity-density-product material (or equivalently a high conductivity-to-density ...
Resistivity and conductivity are reciprocals: = /. Resistivity is a measure of the material's ability to oppose electric current. This formula is not exact, as it assumes the current density is totally uniform in the conductor, which is not always true in practical situations. However, this formula still provides a good approximation for long ...
The electrical resistance of a uniform conductor is given in terms of resistivity by: [40] = where ℓ is the length of the conductor in SI units of meters, a is the cross-sectional area (for a round wire a = πr 2 if r is radius) in units of meters squared, and ρ is the resistivity in units of ohm·meters.
Electrical resistance surveys (also called earth resistance or resistivity survey) are one of a number of methods used in archaeological geophysics, as well as in engineering geology investigations. In this type of survey electrical resistance meters are used to detect and map subsurface archaeological features and patterning.
The red curve shows the power in the load, normalized relative to its maximum possible. The dark blue curve shows the efficiency η. The efficiency η is the ratio of the power dissipated by the load resistance R L to the total power dissipated by the circuit (which includes the voltage source's resistance of R S as well as R L):
Some materials such as glass, paper and PTFE, which have high resistivity, are very good electrical insulators. A much larger class of materials, even though they may have lower bulk resistivity, are still good enough to prevent significant current from flowing at normally used voltages, and thus are employed as insulation for electrical wiring ...
The voltage v and current i variables in an electrical component must be defined according to the passive sign convention; positive conventional current is defined to enter the positive voltage terminal; this means power P flowing from the circuit into the component is defined to be positive, while power flowing from the component into the circuit is negative.