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The SI unit of electrical resistivity is the ohm-metre (Ω⋅m). [1] [2] [3] For example, if a 1 m 3 solid cube of material has sheet contacts on two opposite faces, and the resistance between these contacts is 1 Ω, then the resistivity of the material is 1 Ω⋅m.
Examples of ohmic components are wires and resistors. The current–voltage graph of an ohmic device consists of a straight line through the origin with positive slope . Other components and materials used in electronics do not obey Ohm's law; the current is not proportional to the voltage, so the resistance varies with the voltage and current ...
As quoted in an online version of: David R. Lide (ed), CRC Handbook of Chemistry and Physics, 84th Edition.CRC Press. Boca Raton, Florida, 2003; Section 4, Properties of the Elements and Inorganic Compounds; Physical Properties of the Rare Earth Metals
Sheet resistance is a special case of resistivity for a uniform sheet thickness. Commonly, resistivity (also known as bulk resistivity, specific electrical resistivity, or volume resistivity) is in units of Ω·m, which is more completely stated in units of Ω·m 2 /m (Ω·area/length). When divided by the sheet thickness (m), the units are Ω ...
The units of specific contact resistivity are typically therefore in ohm-square metre, or Ω⋅m 2. When the current is a linear function of the voltage, the device is said to have ohmic contacts. Inductive and capacitive methods could be used in principle to measure an intrinsic impedance without the complication of contact resistance.
The completed resistor was painted for color-coding of its value. The resistive element in carbon composition resistors is made from a mixture of finely powdered carbon and an insulating material, usually ceramic. A resin holds the mixture together. The resistance is determined by the ratio of the fill material (the powdered ceramic) to the carbon.
This alloy has, for example, an adequately high strain sensitivity, or gauge factor, which is relatively insensitive to strain level and temperature. Its resistivity ( 5.00 × 10 −7 Ω·m ) [ 2 ] is high enough to achieve suitable resistance values in even very small grids, and its temperature coefficient of resistance is fairly low.
Most materials, including the ordinary (positive) resistances encountered in electrical circuits, obey Ohm's law; the current through them is proportional to the voltage over a wide range. [4] So the I–V curve of an ohmic resistance is a straight line through the origin with positive slope.