What Is Electrical Resistivity?

Resistivity is a physical quantity used to represent the resistance characteristics of various materials. The resistance of a conductor made of a material with a length of 1 meter and a cross-sectional area of 1 square meter is numerically equal to the resistivity of this material. It reflects the property of the material to hinder the current, it is related to the type of the material, and it is also affected by temperature ^[1] .

Resistivity is a physical quantity used to express the resistance characteristics of various substances. The resistance of a conductor made of a material with a length of 1 meter and a cross-sectional area of 1 meter ² is numerically equal to the resistivity of this material ^[2]

Resistivity (resistivity) is a physical quantity used to indicate the resistance characteristics of various substances. At a certain temperature, the resistance of the material is: ^[4]

1. Resistivity is not only related to the material of the conductor, but also to the temperature of the conductor. In the range where the temperature does not change much, the resistivity of almost all metals changes linearly with temperature, that is, = ₀ (1 + at), where t is the Celsius temperature, and is the resistivity at 0 ° C, a It is the temperature coefficient of resistivity. Using this property, it can be made into a resistance thermometer. The resistance of some alloys is little affected by temperature. It is often used as a standard resistance ^[5]

Resistivity is not only related to the type of material, but also to external factors such as temperature, pressure, and magnetic fields. When the temperature of the metal material is not high, the relationship between and temperature t () is _t = ₀ (1 + at), where _t and ₀ are the resistivities at t and 0 , respectively; a is The temperature coefficient of resistivity is related to the material. The a of manganese copper is about 1 × 10 ^-5 / (its value is extremely small). The resistance value of the resistor made with it is extremely small with temperature change in the normal temperature range, which is suitable for standard resistance. Knowing the regularity of the material's value with temperature, a resistance thermometer can be made to measure the temperature. Alpha of a semiconductor material is generally negative and has a large magnitude. The manufactured resistance thermometer has high sensitivity. Some metals (such as Nb and Pb) or their compounds, when the temperature drops to a few K or dozens of K (absolute temperature), suddenly decreases to close to zero, superconducting phenomenon appears, superconducting materials have a wide range of application prospects. Using the properties of the material's that changes with the magnetic field or the stress, it can be made into a magnetoresistive resistor or a resistance strain gauge, which can be used to measure the mechanical stress on the magnetic field or the object, and has been widely used in engineering ^[6]

Common metal conductor resistivity ( · m): ^[7]

Resistivity is a physical quantity that reflects the conductivity of a conductor. Small resistivity, good conductivity; large resistivity, poor conductivity. The resistivity is determined by the nature of the material, and the resistivity of the same material changes with temperature. Generally, the temperature is high and the resistivity is large. The following table lists the resistivities of some common materials at room temperature ^[8] .

As can be seen from the table above, the resistivities of metals and alloys are small; the resistivities of bakelite and rubber are very large. In use, you can select a suitable material by referring to the resistivity table as needed. For example, in the power supply, transmission, and distribution lines, in order to reduce the resistance, low-resistivity materials such as copper and aluminum are used to make the wires; and the insulation parts of electrical appliances and electrical tools must be high in bakelite and rubber. Resistive material for making wires ^[8] .

When assembling special wires for high energy-consuming appliances such as air conditioners, because of their large power and large working current, we often choose copper wires with smaller resistivity and larger wire diameters ^[8] .

The resistivity of various materials varies with temperature. The resistivity of pure metals increases with increasing temperature. Resistance thermometers are made of this characteristic of metals and can be used to measure very high temperatures. Precision resistance thermometers are made of platinum. Knowing the relationship between the resistance of platinum wire and temperature, you can know the ambient temperature by measuring the resistance of platinum wire. Some alloys, such as manganese copper and constantan alloy, are almost unaffected by temperature changes, and are often used to make standard resistors ^{[8] [9]} .