Textbook for Operation and Maintenance Engineer of Power and Environment Specialty of Data Center - Resistance and Resistance Law - Classification of substances

 1.1.4.2 Resistance
The free electrons in the conductor move directionally under the action of electric field force, forming current. The free electrons in directional motion must collide with the atomic nucleus which vibrates constantly near the equilibrium position, preventing the directional motion of free electrons. This blocking effect reduces the average speed of the directional movement of free electrons, and a part of the kinetic energy of free electrons is converted into the heat energy of molecular thermal movement. The physical quantity representing this blocking effect is called resistance, which is represented by the letter R. Any object has a resistance, and when there is a current flowing through it, it will consume a certain amount of energy.
1.1.4.3 Resistance law
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wire mesh cable tray Grid cable tray basket cable trayThe outer electrons of the atomic nucleus of the insulator have great attraction. raised floor access floor ALL STEEL PANEL CALCIUM SULPHATE PANEL ALUMINUM PANEL OA FLOOR The size of the conductor resistance is not only related to the material of the conductor, but also to the size of the conductor. Experiments have proved that the resistance of a conductor made of a certain material is proportional to its length and inversely proportional to its cross-sectional area when the temperature is constant. This experimental rule is called the law of resistance. The resistance of a uniform conductor can be expressed as
l
R = ρ
s
Where, ρ— The resistivity is determined by the properties of the conductor material, in ohm meters, with the symbol of Ω · m, as shown in Table 1.1-1;
L - length of conductor, unit: m, symbol: m;
S - sectional area of conductor, unit: m2;
R - resistance of conductor, unit: Ω, symbol: Ω.
In the International System of Units, the common units of resistance are kiloohm (K Ω) and megaohm (M Ω): 1K Ω=103 Ω
1M Ω ＝103K Ω ＝106 Ω
The resistivity of several common materials at 20 ℃ is shown in Table 1.1-1.

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Textbook for Operation and Maintenance Engineer of Power and Environment Specialty of Data Center - Resistance and Resistance Law - Classification of substances