l>Copper and electricity. Resistance and also resisitivty.

You are watching: The resistivity of a wire depends on

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page 4
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Resistanceandresistivity
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Bulk properties
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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.

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Picture 2.2 Graph the resistivities of some metals.
Some resistivities
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.
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Picture 2.3 Graphics come illustrate just how resistance varies through l, A and rho.
Calculating resistance
To calculation the resistance R the a wire, we require to recognize three things:its length
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–the longer the wire, the better its resistanceits cross-sectional area A–the 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

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This equation defines resistivity. We deserve to rearrange that to gain a formula because that resistivity:

resistivity = resistance × area / length

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Question 3
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.