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|Picture 2.2 The high conductivity the copper makes it an ideal for this electrode holder which carries enormous currents to a steel making arc furnace.|
When we say the copper is a heavier metal than aluminium, we are comparing their densities. In a similar way, once we say the copper is a better conductor than aluminium, we are comparing your resistivities.
Density and resistivity room both bulk properties of a material. Their value doesn"t depend on the size or form of a details sample just on the material itself.
Resistivity: depends on the product onlyResistance: counts on size and also shape - and also on the material.
|What is resistivity?|
|In effect, the resistivity to represent the resistance across two opposite encounters of a cubic metre of material (in the same method that density is the fixed of a cubic metre). Resistivity tells just how resistive a product is.|
Resistivity has actually the prize r - (rho to rhyme with snow) and also its units room ohm metres.
|Picture 2.2 Graph the resistivities of some metals.|
|Table 3 reflects some resistivities. Girlfriend will check out that resistivity varies from about 10-8Wm to more than 1016Wm an ext than 24 order of magnitude. No various other property of materials varies over such a large range.|
|Picture 2.3 Graphics come illustrate just how resistance varies through l, A and rho.|
|To calculation the resistance R the a wire, we require to recognize three things:its length |
the longer the wire, the better its resistanceits cross-sectional area Athe greater the area, the much less its resistancethe resistivity that the material r the better the resistivity, the better its resistance.
resistance = resistivity × size / area
This equation defines resistivity. We deserve to rearrange that to gain a formula because that resistivity:
resistivity = resistance × area / length
|a) Look in ~ the electrode holder in the photo at the optimal of the page. Usage the table to to compare the resistivities that copper and steel; use this to describe why using copper is an energy-efficient choice.|
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b) A wire made that a copper alloy is 5m in length and also has a cross-sectional area 1mm2. That resistance is 0.15W. Calculation the resistivity the this alloy.