Electrical resistance

Hard Rubber As seen in the table, there is a broad range of resistivity values for various materials.

Electrical resistance

Causes of conductivity[ edit ] See also: Band theory Filling of the electronic states in various types of materials at equilibrium. Here, height is energy while width is the density of available states for a certain energy in the material listed. In metals and semimetals the Fermi level EF lies inside at least one band.

In insulators and semiconductors the Fermi level is inside a band gap ; however, in semiconductors the bands are near enough to Electrical resistance Fermi level to be thermally populated with electrons or holes.

When a large number of such allowed energy levels are spaced close together in energy-space —i. So the electrons "fill up" the band structure starting from the bottom.

The characteristic energy level up to which the electrons have filled is called the Fermi level. The position of the Fermi level with respect to the band structure is very important for electrical conduction: In contrast, the low energy states are rigidly filled with a fixed number of electrons at all times, and the high energy states are empty of electrons at all times.

Electric current consists of a flow of electrons. In metals there are many electron energy levels near the Fermi level, so there are many electrons available to Electrical resistance. This is what causes the high electronic conductivity of metals. An important part of band theory is that there may be forbidden bands of energy: In insulators and semiconductors, the number of electrons is just the right amount to fill a certain integer number of low energy bands, exactly to the boundary.

In this case, the Fermi level falls within a band gap. Since there are no available states near the Fermi level, and the electrons are not freely movable, the electronic conductivity is very low.


Free electron model A metal consists of a lattice of atomseach with an outer shell of electrons that freely dissociate from their parent atoms and travel through the lattice. This is also known as a positive ionic lattice. When an electrical potential difference a voltage is applied across the metal, the resulting electric field causes electrons to drift towards the positive terminal.

Electrical resistance

The actual drift velocity of electrons is typically small, on the order of magnitude of meters per hour. However, due to the sheer number of moving electrons, even a slow drift velocity results in a large current density. Most metals have electrical resistance. In simpler models non quantum mechanical models this can be explained by replacing electrons and the crystal lattice by a wave-like structure.

When the electron wave travels through the lattice, the waves interferewhich causes resistance.

Electrical resistance (R) - tranceformingnlp.com

The more regular the lattice is, the less disturbance happens and thus the less resistance. The amount of resistance is thus mainly caused by two factors.

The traditional low-voltage Electrical Resistance method of heat treating uses ceramic blankets stepped down to 80 volts to provide a quick and convenient approach to . The electrical resistance of a circuit component or device is defined as the ratio of the voltage applied to the electric current whichflows through it. If the resistance is constant over a considerable range of voltage, then Ohm's law, I = V/R, can be used to predict the behavior of the material. The traditional low-voltage Electrical Resistance method of heat treating uses ceramic blankets stepped down to 80 volts to provide a quick and convenient approach to .

First, it is caused by the temperature and thus amount of vibration of the crystal lattice. The temperature causes bigger vibrations, which act as irregularities in the lattice.

Second, the purity of the metal is relevant as a mixture of different ions is also an irregularity.

Contrasting student and scientific views

Semiconductor and Insulator electricity In metals, the Fermi level lies in the conduction band see Band Theory, above giving rise to free conduction electrons.

However, in semiconductors the position of the Fermi level is within the band gap, about halfway between the conduction band minimum the bottom of the first band of unfilled electron energy levels and the valence band maximum the top of the band below the conduction band, of filled electron energy levels.

That applies for intrinsic undoped semiconductors. This means that at absolute zero temperature, there would be no free conduction electrons, and the resistance is infinite. However, the resistance decreases as the charge carrier density i.

In extrinsic doped semiconductors, dopant atoms increase the majority charge carrier concentration by donating electrons to the conduction band or producing holes in the valence band. A "hole" is a position where an electron is missing; such holes can behave in a similar way to electrons.


For both types of donor or acceptor atoms, increasing dopant density reduces resistance. Hence, highly doped semiconductors behave metallically. At very high temperatures, the contribution of thermally generated carriers dominates over the contribution from dopant atoms, and the resistance decreases exponentially with temperature.

Conductivity electrolytic In electrolyteselectrical conduction happens not by band electrons or holes, but by full atomic species ions traveling, each carrying an electrical charge.

The resistivity of ionic solutions electrolytes varies tremendously with concentration — while distilled water is almost an insulator, salt water is a reasonable electrical conductor.

Conduction in ionic liquids is also controlled by the movement of ions, but here we are talking about molten salts rather than solvated ions.The traditional low-voltage Electrical Resistance method of heat treating uses ceramic blankets stepped down to 80 volts to provide a quick and convenient approach to .

The electrical resistance of an electrical conductor is the opposition to the passage of an electric current through that conductor; the inverse amount is electrical conductance. The electrical resistance of an electrical conductor is a measure of the difficulty to pass an electric current through that conductor.

The inverse quantity is electrical conductance, and is the ease with which an electric current passes. Electrical resistivity (also known as specific electrical resistance, or volume resistivity) is a fundamental property of a material that quantifies how strongly that material opposes the flow of electric current.A low resistivity indicates a material that readily allows the flow of electric current.

Resistivity is commonly represented by the Greek letter ρ (). The resistance of an object determines the amount of current through the object for a given potential difference (voltage) across the object. Thus, electrical resistance is equal to the ratio of voltage divided by electric current.

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