1. Factors affecting resistivity
Resistivity is a physical quantity used to express the electrical resistance of various substances. The ratio of the product of the resistance and cross-sectional area of the component made of a substance (20°C at room temperature) to its length is called the resistivity of the substance. The unit of electrical resistivity in the SI system of units is the ω ·m, pronounced ohm, or omega for short. The common unit is "ohm · cm".
Resistivity has nothing to do with the length of the conductor, cross-sectional area and other factors, but is the electrical properties of the conductor material itself, determined by the conductor material, and related to temperature, pressure, magnetic field and other external factors. The relationship between ρ and temperature t (℃) is ρt=ρ0 (1+at), in which ρ1 and ρ0 are the resistivity at T ℃ and 0℃ respectively. α is a temperature coefficient of resistivity, material dependent. The α of manganese copper is about 1×10-1/℃ (its value is very small). The resistance value of the resistor made of manganese copper changes very little with temperature in the normal temperature range, so it is suitable for standard resistance. A resistance thermometer can be made to measure temperature when the ρ value of the material changes with temperature. The α of semiconductor materials is generally negative and has a large magnitude. The resistance thermometer has high sensitivity. Some metals (such as Nb and Pb) or their compounds, when the temperature drops to a few K or more than ten K (absolute temperature), the ρ suddenly decreases to close to zero, superconducting phenomenon, superconducting materials have a wide range of application prospects. Magnetosensitive resistance or resistance strain gauge can be made by using the property that the ρ of material changes with magnetic field or stress, which can be used to measure the mechanical stress of magnetic field or object respectively, and it is widely used in engineering.
This picture is provided by registered user "Orange de Palace", feedback of copyright statement
Second, the calculation method of resistivity
The calculation formula of resistivity is as follows:
ρ is the resistivity, usually in the unit ω ·m
S is the cross-sectional area -- common units ㎡
R is the resistance value -- the common unit ω
L is the length of the wire -- usually in m
Rho = Rs/L
Another formula for calculating resistivity is:
ρ is resistivity -- commonly used unit ω ·mm2/m
E is the strength of the electric field -- usually N/C
J is the current density -- commonly used unit A/㎡
(E, J can be vectors)
Rho = E/J
Three, the application of resistivity
Materials with low resistivity are called conductors. Common conductors are mainly metals. Silver is the best conductor in nature, followed by semiconductor, silicon and germanium. When there is an external electric field, the free electrons of the metal constantly collide with the positive ions of the thermal oscillator on the lattice node in the process of movement, so that the movement of the electrons is hindered, so that there is a certain resistance. Other materials that are not easy to conduct electricity, such as glass and rubber, have high resistivity and are generally called insulators. A substance (such as silicon) that lies between a conductor and an insulator is a semiconductor. The scientific symbol for resistivity is ρ (Rho). Known the resistance of the object, can be calculated by the resistivity ρ, length L and section area A: ρ=RA/I, in the formula, resistance R unit for ohm, length L unit for meters, section area A unit for square meters, resistivity ρ unit for ohm · meters.