# Electrical conductivity

Photo by: demarco

Electrical conductivity is the ability of a material to carry the flow of an electric current (a flow of electrons). Imagine that you attach the two ends of a battery to a bar of iron and a galvanometer. (A galvanometer is an instrument for measuring the flow of electric current.) When this connection is made, the galvanometer shows that electric current is flowing through the iron bar. The iron bar can be said to be a conductor of electric current.

Replacing the iron bar in this system with other materials produces different galvanometer readings. Other metals also conduct an electric current, but to different extents. If a bar of silver or aluminum is used, the galvanometer shows a greater flow of electrical current than with the iron bar. Silver and aluminum are better conductors of electricity than is iron. If a lead bar is inserted, the galvanometer shows a lower reading than with iron. Lead is a poorer conductor of electricity than are silver, aluminum, or iron.

Many materials can be substituted for the original iron bar that will produce a zero reading on the galvanometer. These materials do not permit the flow of electric current at all. They are said to be nonconductors, or insulators. Wood, paper, and most plastics are common examples of insulators.

## Electrical Resistance

Another way of describing the conductivity of a material is through resistance. Resistance can be defined as the extent to which a material prevents the flow of electricity. Silver, aluminum, iron and other metals have a low resistance (and a high conductivity). Wood, paper, and most plastics have a high resistance (and a low conductivity).

The unit of measurement for electrical resistance is called the ohm (abbreviation: Ω). The ohm was named for German physicist Georg Simon Ohm (1789–1854), who first expressed the mathematical laws of electrical conductance and resistance in detail. Interestingly enough, the unit of electrical conductance is called the mho (ohm written backwards). This choice of units clearly illustrates the reciprocal (opposite) relationship between electrical resistance and conductivity.

## How conductance takes place

Electrical conductivity occurs because of the ease with which electrons can be removed from atoms. All substances consist of atoms. In turn, all atoms consist of two main parts: a positively charged nucleus and one or more negatively charged electrons. An atom of iron, for example, consists of a nucleus with 26 positive charges and 26 negatively charged electrons.

The electrons in an atom are not all held with equal strength. Electrons close to the nucleus are strongly attracted by the positive charge of the nucleus and are removed from the atom only with great difficulty. Electrons farthest from the nucleus are held only loosely and are removed quite easily.

A block of iron can be thought of as a huge collection of iron atoms. Most of the electrons in these atoms are held tightly by the iron nuclei. But a few electrons are held loosely—so loosely that they act as if they don't even belong to atoms at all. Scientists sometimes refer to this condition as a cloud of electrons.

Normally these "free" electrons have no place to go. They just spin around randomly among the iron atoms. That situation changes, however, when a battery (or other source of electric current) is attached to the iron block. Electrons flow out of one end of the battery and into the other. At the electron-rich end of the battery, electrons flow into the piece of iron, pushing iron electrons ahead of them. Since all electrons have the same negative charge, they repel each other. Iron electrons are pushed away from the electron-rich end of the battery towards the electron-poor end. In other words, an electric current flows through the iron.

Insulators have a very different structure. They too consist of atoms (nuclei and electrons), but very few free electrons can be found in insulators. Those electrons tend to be bound tightly to nuclei in chemical bonds. Attaching a battery to an insulator has no effect since there are no free electrons to be pushed through the material.

## Solution conductivity

Electrons are not the only particles capable of carrying an electric current. Ions can do it, too. An ion is an atom or group of atoms with an electric charge. Suppose you dissolve a crystal of table salt (sodium chloride) in water. Salt crystals consist of positive sodium ions and negative chloride ions. In the solid state, these ions are not free to move around. Once they are dissolved in water, however, they become completely mobile. They are free to "swim" about in the water and to respond to an electric current from a battery. That current supplies electrons that cause positive sodium ions to flow in one direction and negative chloride ions to flow in the opposite direction.

A good example of this effect can be seen in the conductivity of water. Pure water consists only of water molecules. The electrons in water molecules are held tightly by hydrogen and oxygen atoms and are not free to move. Attaching a battery to a container of water produces no electric current because pure water is an insulator. But a few grains of table salt added to the water changes things completely. Sodium ions and chloride ions are released from the salt, and the salt water solution becomes conductive.

## Semiconductivity and superconductivity

Some materials cannot be classified as either conductors or insulators. Semiconductors, for example, are materials that conduct an electric current but do so very poorly. Semiconductors were not well understood until the mid-twentieth century, when a series of remarkable discoveries revolutionized the field of electrical conductivity. These discoveries have made possible a virtually limitless variety of electronic devices, ranging from miniature radios and handheld calculators to massive solar power arrays and orbiting telescopes.

Superconductivity is a property that appears only at very low temperatures, usually close to absolute zero (−273°C). At such temperatures, certain materials lose all resistance to electric current; they become perfect conductors. Once an electric current is initiated in such materials, it continues to flow without diminishing and can go on essentially forever.

The discovery of superconductivity holds enormous potential for the development of electric appliances. In such appliances, a large fraction of the electrical energy supplied to the device is lost in overcoming electrical resistance within the device. That lost energy shows up as waste heat. If the same appliance were made of a superconducting material, no energy would be lost because there would be no resistance to overcome. The appliance would become, at least in principle, 100 percent efficient.

## User Contributions:

atom
I did an experiment about Estimating the Concentration of Total Dissolved Ionizable Soilds by Conductivity , my solution was Nacl
i have 10 solution with different concentration and i measured the conductivity of each of them . I need to calculate the concentration of Cl- ion by this result, How can I >
is it the slope of the graph between conductivity and volume ??

thank you
kim redder
If a "live" electrical wire falls on the metal roof of a bus, will it electrify the metal parts of the bus? Will the bus conduct the electrical current from the wire even though it has rubber tires?
Jessie
Hi,
I have a question...
What is the effect upon loosely held electrons in an object? Like, would electricty flow easier? What would the electrons act like, will they gain anything?
Thanks...
-Jessie-
JACK
Hi!
I have a question:

Al2O3 is doped in NiO and the Al3+ will enter the lattice site of Ni2+. So, how the Al3+ ion doping influence the electric conductivity of NiO. After Al3+ is doped in NiO, what is the relationship between the electron hole concentration in NiO and the oxygen partial pressure in the environment?

if no direct answer you can suggest me the literature to read
Thank you!
Hello. I think this website is very beneficial for children's educational purposes. Xxx
when the electrons flow in the metal ,how the current was produced?
Attempting to see which fruits will light an LED the longest but I don't know anything about electricity but I heard that acidity will make a difference. Will you please help guide me as to what I need to understand before starting my experiment? Like conductivity or current?
Ksenchy
HI,
I'm working on project "Electrical conductivity of molten salts". It's a four electrode setup at high temperatures (around 1500 Celsius degrees). Does anyone has anything about this work?
Thank you!
Materials Guy
Strictly speaking, where you mention resistance, you should be referring to it as resistivity. Resistance is a function of the materials intrinsic resistivity AS WELL AS the geometric factors of the conducting medium. So it is inaccurate to say the resistance and conductivity are inversely related. It should be that the conductivity and resistivity are inversely related since they are intrinsic materials properties. Similarly, conductance and resistance are inversely related since both of those terms account for the geometric factors. The can also be seen by the fact that the units of resistivity are Ohm meters or Ohm centimeters.
EXCELLENT BUT INEED THE BASICS ABOUT HOW THE HOLES AND ELCTRONS WERE PATICIPATE IN THE CONDUCTION AT A ITME
Hi
can you please tell me what is the unit of water conductivity .
what is electrical conductivity of wood and its relationship with resistivity? how this mechanism works in a moisture meter.\?
When is a substance said to be a conductor under a physical case.
Ong Siew Hong
I have a question and correct me if I'm wrong. As far as I understand, brass is a better electrical conductance than phosphorus bronze, eventhough the copper content in phosphorus bronze is > 95% whereas brass is normally about > 60%, as the electrical conductivity of phosphorus bronze is depleted by the very small content of phosphorus. Despite of the above, many electrical products in the market, choose to use phos bronze for its parts that require better spring tension, but being a poor electrical conductance, is it a right decision to use bronze for its contact than using a harder brass as substitute ? Anyone able to advise ? Thank you
tanyi
hi
pls wat does the graph of conductivity to resistance look like.
tanyi
Prags
What I would like to know is how this relates to real life. I want to include this in the discussion for an experiment for school but am struggling with ideas. Please help asap.
Eze
Why is electrical resistance mostly used to characterize conductivity instead of conductance?