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What is resistance Ohms Law Ohmic & Non-Ohmic conductors Resistance of filament lamp Resistivity Resistivity table for common materials Resistance temperature coefficient Electrical conductivity Series & parallel resistors Parallel resistors table
The table of electrical resistivity below contains the values of resistivity for many of the substances widely used in electronics. In particular it includes the resistivity of copper, the resistivity of aluminium, gold and silver.
The electrical resistivity is particularly important because it will determine its electrical performance and hence whether it is suitable for use in many electrical components. For example it will be seen that the resistivity of copper, the resistivity of aluminium and that of silver and gold determines where these metals are used.
In order to compare the capability of different materials to carry electrical current, figures for the resistivity are used.
What do resistivity figures mean
In order to be able to compare the resistivity of different materials from items like copper and silver to other metals and substances including bismuth, brass and even semiconductors, a standard measurement must be used.
The definition of resistivity states that the resistivity of a substance is the resistance of a cube of that substance having edges of unit length, with the understanding that the current flows normal to opposite faces and is distributed uniformly over them.
Resistivity is normally measured in Ohm metres. This means that the resistivity is measured for cube of the material measuring a metre in each direction.
Table of resistivity for common materials
The table below gives the resistivity figures for a variety of materials, particularly metals used as electrical conduction.
The resistivity figures are given for materials including copper, silver, gold, aluminium, brass and the like.
|Table of Electrical Resistivity for Common Materials
|Material||Electrical Resistivity at 20°C
|Aluminium||2.8 x 10-8|
|Antimony||3.9 x 10-7|
|Bismuth||1.3 x 10-6|
|Brass||~0.6 - 0.9 x 10-7|
|Cadmium||6 x 10-8|
|Cobalt||5.6 x 10-8|
|Copper||1.7 x 10-8|
|Gold||2.4 x 10-8|
|Carbon (Graphite)||1 x 10-5|
|Germanium||4.6 x 10-1|
|Iron||1.0 x 10-7|
|Lead||1.9 x 10-7|
|Manganin||4.2 x 10-7|
|Nichrome||1.1 x 10-6|
|Nickel||7 x 10-8|
|Palladium||1.0 x 10-7|
|Platinum||0.98 x 10-7|
|Quartz||7 x 1017|
|Silicon||6.4 x 102|
|Silver||1.6 x 10-8|
|Tantalum||1.3 x 10-7|
|Tin||1.1 x 10-7|
|Tungsten||4.9 x 10-8|
|Zinc||5.5 x 10-8|
Resistivity of materials - which is best
It can be seen that the resistivity of copper and the resistivity of brass both low and in view of their cost, relative to silver and gold, they become cost effective materials to use for many wires. The resistivity of copper and its ease of use mean that it is also used almost exclusively for the conductor material on printed circuit boards.
Aluminium occasionally and particularly copper are used for their low levels of resistivity. Most wire used these days for interconnections is made from copper as it offers a low level of resistivity at an acceptable cost.
The resistivity of gold is also important because gold is used in some critical areas despite its cost. Often gold plating is found on high quality low current connectors where it ensures the lowest contact resistance. The gold plating is very thin, but even so it is able to provide the required performance in the connectors.
Silver has a very low level of resistivity but it is not so widely used because of its cost and because it tarnishes which this can result in higher contact resistances. The oxide can act as a rectifier under some circumstance which may cause some annoying problems in RF circuits, generating what are termed passive intermodulation products.
However it was used in some coils for radio transmitters where the low electrical resistivity of the silver reduced the losses. When used into is application, it was normally only plated onto an existing copper wire - the skin effect that affects higher frequency signals meant that only the surface of the wire was used for the conduction of the high frequency electrical currents. By plating the wire with silver, this significantly reduced the costs compared to a solid silver wire without any significant on performance.
Other materials in the electrical resistivity table may not have such obvious applications. Tantalum appears in the table because it is used in capacitors - nickel and palladium are used in the end connections for many surface mount components such as capacitors.
Quartz finds its main use as a piezo-electric resonant element. Quartz crystals are used as frequency determining elements in many oscillators where its high value of Q enables very frequency stable circuits to be made. They are similarly used in high performance filters. Quartz has a very high level of resistivity and it is not a good conductor of electricity, being categorised as an insulator.
Resistivity classifications for conductors, insulators, semiconductors
There are three broad classifications of materials in terms of their resistivity: conductors, semiconductors and insulators.
|Comparison of Resistivity of Conductors, semiconductors and insulators
|Material||Typical Resistivity Range (Ωm)|
|Conductors||10-2 - 10-8|
|Semiconductors||10-6 - 106|
|Insulators||1011 - 1019|
These figures are only a guide. The figures for semiconductors will depend greatly on the level of doping.
Electrical resistivity of materials is a key electrical parameter. It governs whether materials can be used effectively in many electrical and electronic applications. It is a key parameter that is used for determining the right materials to be used within electrical and electronic items.
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Voltage Current Power Resistance Capacitance Inductance Transformers Decibel, dB Kirchoff's Laws Q, quality factor RF noise
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