Electrical Resistivity | Formula Units | catchsomeair.us
Differentiate between resistance and resistivity; Define the term and resistivity; State the relationship between resistivity and temperature. Use resistivity to calculate the resistance of specified configurations of material. The resistance of an object depends on its shape and the material of which it is. Resistance and Resistivity. Electric resistance is measured in ohms: 1 volt 1 ohm = 1 amp; The resistance of a wire or rod to the flow of electric current.
Type the name of the material and click the Submit button to find its resistivity. Mathematical Nature of Resistance Resistance is a numerical quantity that can be measured and expressed mathematically.
Electric Resistance – The Physics Hypertextbook
The standard metric unit for resistance is the ohm, represented by the Greek letter omega. The equation representing the dependency of the resistance R of a cylindrically shaped conductor e. Consistent with the discussion above, this equation shows that the resistance of a wire is directly proportional to the length of the wire and inversely proportional to the cross-sectional area of the wire.
As shown by the equation, knowing the length, cross-sectional area and the material that a wire is made of and thus, its resistivity allows one to determine the resistance of the wire. Resistors are one of the more common components in electrical circuits. Most resistors have stripes or bands of colors painted on them. The colors reveal information about the resistance value.
- Resistivity basics
- Material and shape dependence of resistance
- Electrical resistivity units
Perhaps you're doing a lab and need to know the resistance of a resistor used in the lab. The resistance and conductance of a wire, resistor, or other element is mostly determined by two properties: In the same way, a long, thin copper wire has higher resistance lower conductance than a short, thick copper wire.
Materials are important as well. A pipe filled with hair restricts the flow of water more than a clean pipe of the same shape and size. Similarly, electrons can flow freely and easily through a copper wire, but cannot flow as easily through a steel wire of the same shape and size, and they essentially cannot flow at all through an insulator like rubberregardless of its shape. The difference between copper, steel, and rubber is related to their microscopic structure and electron configurationand is quantified by a property called resistivity.
In addition to geometry and material, there are various other factors that influence resistance and conductance, such as temperature; see below. Conductors and resistors[ edit ] A 6.
An ohmmeter could be used to verify this value. Substances in which electricity can flow are called conductors. A piece of conducting material of a particular resistance meant for use in a circuit is called a resistor. Conductors are made of high- conductivity materials such as metals, in particular copper and aluminium.
Resistors, on the other hand, are made of a wide variety of materials depending on factors such as the desired resistance, amount of energy that it needs to dissipate, precision, and costs.
Ohm's law The current-voltage characteristics of four devices: Two resistorsa diodeand a battery. The horizontal axis is voltage dropthe vertical axis is current.
Second, the purity of the metal is relevant as a mixture of different ions is also an irregularity.
9.3: Resistivity and Resistance
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.
Difference Between Resistance & Resistivity with Comparison Chart - Circuit Globe
In biological membranescurrents are carried by ionic salts. Small holes in cell membranes, called ion channelsare selective to specific ions and determine the membrane resistance. Superconductivity The electrical resistivity of a metallic conductor decreases gradually as temperature is lowered. In ordinary conductors, such as copper or silverthis decrease is limited by impurities and other defects.