How does the conductivity measure resistivity of copper rod

How does the conductivity measure resistivity of copper rod

How to test resistivity of copper rod

The resistivity of copper Ω was 0.0175/m,pure copper resistivity in 20℃ is:1.7376X10^ -8 Ω·meter(欧·米)

Resistance is resistivity times length divided by cross-sectional area,calculate.

Resistivity (resistivity) is used to represent various substances resistance characteristic quantities .some material of 1m long,cross-sectional area is 1square millimeters at room temperature (20℃) conductor resistance,called the resistivity of the material.

In the international system of units,the unit of the resistivity is the ·m(Ω·m or ohmm) ,commonly used unit is ohm square mm/m

The calculating formula of resistivity

The resistivity of the calculation formula is :Rho=RS/L。

ρRho-commonly used units for resistivity Ωm

S For the cross-sectional area,commonly used unit ㎡

R For Ω resistance-common unit

L Is the length of the wire-a common units

1. Resistivity ρ is not only related ti the conductor materials,but also   related to the temperature of the conductor.in the range of certain temperature change,almost all the resistivity of the metal linear change with temperature,namely ρ=ρo(1+at),the t is the Celsius temperature,ρo is resistivity when it is 0℃ ,a is coefficient of resistivity temperature .

2. Because of the resistivity changes with temperature changes,so to some electrical resistance,it must be showed what is their physical condition.such as a 220v,100w lamp filament resistance,when electrified is 484Ω，not be electrified is only about 40Ω。

Resistivity and resistance are two different concepts,resistivity is property that reflecting the material has impeding function on electricity ,the resistance reflects that the object has impeding function on electricity .

The use of the resistivity ,resistivity divided by the thickness of the metal film to get the so-called square resistance,measure the amount of resistance is commonly used in engineering application is a resistivity and another is a square resistance:the result of resistance is equal to the square resistance times the metal block ratio of the length and width. 

High temperature accelerated electronic movement,increases the chances of electrons are scattered so the heated object has higher resistance .

The metal with a transverse section and with large area has more space for electronic movement ,so the resistance is lower。 

When Electronic across the long metal ,generally more collision will happen,so long metal resistance is larger.

The temperature has different affects on different material resistance value

High temperature accelerate the electronic movement ,improve the chances of being scatter,so the heated objects have high resistance.

Here is the normal resistivity of metal conductor under 20℃

1.silver 1.65*10-8

2.Copper  1.75*10-8

3.Aluminum 2.83*10-8

4.Tungsten  5.48*10-8

5.Iron 9.78*10-8

6 .platinum 2.22 x 10-7

7. manganese bronze 4.4 x 10-7

8.Mercury 9.6 x 10 (8) - 7

9. constantan 5.0 x 10-7

10. nickel chrome 1.0 x 10 to 6

11. iron chromiumAluminum alloy1.4 x 10 to 6

12. aluminum nickel and iron 1.6 x 10 to 6

13. graphite (8 ~ 13) x 10 to 6

It can be seen that the resistivity of the metal is small,the resistivity of alloy is larger,nonmetal and some metal oxides have larger resistivity ,however,the  resistivity of insulators is the largest.Germanium and silicon,selenium ,copper oxide,boron and other resistivity is smaller than insulator and larger than the metal,we put this kind of material called a semiconductor 。

Normal condition ,(by a chart) the best of conductivity is in turn ,silver ,copper ,aluminum,this is the most commonly used three kinds of material,is often used as a conductor,the copper is used most widely 

Now almost all wires are copper (precision instruments ,except for special occasions) aluminum wire is unstable due to the chemical properties of easy oxidation has been eliminated ,silver has best conductive performance , but due to the high cost so it is less adopted ,used only in the most demanding occasions,such as precision instruments,high frequency oscillators and aerospace,etc,by the way,on some occasions the instrument contact also use gold,because the gold has stable chemical properties ,so it is adopted ,not because of its small resistivity .

The resistivity of other metals

metalTemperature (0 ℃) rho alpha o, 100

zinc20 x 10-3 x 10-3

5.9 4.2

Aluminum (soft)20 2.75 4.2

Aluminum (soft)1.64-78

O romi alloy20 and 1.2

antimony38.7 5.4 0

iridium20 6.5 3.9

indium8.2 5.1 0

invar0 75 2

osmium20 9.5 4.2

cadmium20 7.4 4.2

potassium20 6.9 5.1 (1)

calcium20 4.6 3.3

gold20 2.4 4.0

silver20 1.62 4.1

Chromium (soft)20 17

Romi, nickel chromium alloy (g)- 70-70. 11 -. 54

cobalta 0 6.37 6.58

constantan- 50-04-1.01

zirconium30 and 49 4.0

brass- 5-7 1.4-2

mercury94.08 0.99 0

mercury20 95.8

tin20 11.4 4.5

strontium30.3 3.5 0

bronze18-13-0.5

cesium20 and 4.8

bismuth20 120 4.5

thallium20 (19 May

tungsten20 5.5 5.3

tungsten1000 35

tungsten3000, 123,

tungsten3.2-78

tantalum20 15 3.5

metal Temperature (0 ℃) rho alpha o, 100

Du pull aluminum (soft)- 3.4

Iron (plain)20 9.8 6.6

Iron (plain)4.9-78

Iron (steel)- 10-20 1.5-5

Cast iron ()- 57-114.

Copper (soft)20 1.72 4.3

Copper (soft)100 2.28

Copper (soft)1.03-78

Copper (soft)0.30-183

thorium20 and 2.4

sodium20 4.6 5.5 (1)

lead20 and 4.2

Nickel-chromium alloy (without iron)10 20 109.

Nickel-chromium alloy (iron)20, 95-95. 3 -. 5

Nickel-chromium alloy Lin- 27-45. 2 -. 34

Nickel (soft)20 7.24 6.7

Nickel (soft)3.9-78

platinum20 10.6 3.9

platinum1000-43

platinum6.7-78

Platinum rhodium(2) 20 to 22, 1.4

palladium20 10.8 3.7

arsenic20 to 35 3.9

Nickel copper zinc resistance wire- 34-41. 25-32

Beryllium (soft)6.4 4.0 6.4 mg 20

Manganese bronze42-48-03-20 +. 02

molybdenum20 5.6 4.4

The silver- 17-41. 4 -. 38

lithium20 9.4 4.6

Phosphor bronze6-2 -

Rb.20 12.5 5.5

rhodium20 5.1 4.4

(1) the average temperature coefficient between 0 ℃ and melting point (2) 90% platinum, rhodium if 10% * resistivity unit expressed in ohms cm (Ω cm), 100 times value should be expanded in the table.