Resistance vs. Resistivity
1. Resistance. 1. The conductor has the ability to conduct current, but at the same time it has the effect of hindering the passage of current, which is called the resistance of the conductor, which is represented by the letter R or R, and the unit is ohm, referred to as Europe, and is represented by symbols.
The commonly used units of resistance are megaohms (m), kiloohms (k), milliohms (m), and microohms ( their relationship is 1m = 103;1kω=103ω；1ω=103mω=106μω。
2. When the voltage at both ends of the conductor is 1V and the current in the conductor is 1A, the resistance of this conductor is 1.
That is: 1 = 1v 1a
3. The resistance of the conductor is not only related to the type of material of the conductor, but also related to the geometric size of the conductor.
Experiments show that the resistance of a conductor of the same material is inversely proportional to the cross-sectional area of the conductor and proportional to the length of the conductor.
That is, the longer the conductor, the greater the resistance;The larger the cross-sectional area of the conductor, the smaller the resistance.
The material is uniform, the cross-sectional area s are consistent, and the conductor resistance of the length l can be expressed as:
r=ρl/s
where r--the resistance of the conductor, ;
l--conductor length, m;
s--conductor cross-sectional area, mm2;
Conductor resistivity, mm2 m.
Second, resistivity.
1. The resistivity of a conductor indicates the degree to which the conductor material has resistance to the current.
When the unit of resistance is , the unit of cross-sectional area is mm2, and the unit of length is m, then the unit of resistivity is mm2 m.
2. Resistivity is determined by the material of the conductor, and the resistivity of different materials is different, according to which various materials can be divided into conductors, semiconductors and insulators. An object in which electrons (or ions) in an object move freely is called a conductor. The resistivity of conductors is very small, such as metals and electrolytes are conductors;
Objects with great resistivity are called insulators (also known as dielectrics), and their resistivity is generally greater than 109 ·mm, such as glass, mica, bakelite boards, etcObjects with conductive properties between conductors and insulators are called semiconductors, such as silicon, germanium, etc.
3. The value of conductor resistivity refers to the resistance value of a conductor with a length of 1m and a cross-section of 1mm2 at a temperature of 20.
3. The relationship between conductor resistance and conductor temperature.
1. The resistance value of conductive materials is not only related to the properties of the material itself and the geometric size of the material, but also related to the temperature.
The resistance value of general metal materials such as silver, copper, aluminum, etc. increases with the increase of temperature, but the resistance value of carbon and electrolyte conductors decreases with the increase of temperature.
r2=r1〔1+α(t2-t1)〕
where -- the temperature coefficient of resistance of the conductor material, unit 1.
The temperature coefficient of resistance represents the percentage by which the resistance of a conductor increases by 1 per cent.
That is, the ratio of the change value of the conductor electricity to the original resistance value for every 1 increase in temperature.
Because the temperature coefficient of resistance also changes slightly with different temperatures, the average value in the range of 0-100 is taken in engineering.
r1 -- the resistance value of the conductor at a temperature of t1, ;
r2 – the resistance value of the conductor when the temperature rises to t2.
2. The resistivity and temperature coefficient of commonly used conductive materials can be referred to the following table.