l>Copper and electricity. Resistance and resisitivty.

You are watching: What does the resistivity of a wire depend 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 renders it an ideal for this electrode holder i beg your pardon carries huge currents to a steel making arc furnace.

When us say that copper is a heavier metal than aluminium, we space comparing their densities. In a comparable way, once we say that copper is a much better conductor 보다 aluminium, we are comparing their resistivities.

Density and resistivity are both bulk properties that a material. Their value doesn"t rely on the dimension or shape of a specific sample – only on the product itself.

Resistivity: counts on the product onlyResistance: depends on size and also shape - as well as on the material.

What is resistivity?
In effect, the resistivity represents the resistance throughout two opposite faces of a cubic metre of product (in the same means that thickness is the fixed of a cubic metre). Resistivity tells how resistive a material is.

Resistivity has actually the symbol r - (rho to rhyme v snow) and its units room ohm metres.

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Picture 2.2 Graph the resistivities of part metals.
Some resistivities
Table 3 mirrors some resistivities. You will see that resistivity varies from about 10-8Wm to an ext than 1016Wm – much more than 24 assignment of magnitude. No other property of materials varies over together a vast range.
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Picture 2.3 Graphics to illustrate how resistance varies v l, A and rho.
Calculating resistance
To calculation the resistance R the a wire, we need to understand three things:its size
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–the much longer the wire, the higher its resistanceits cross-sectional area A–the better the area, the much less its resistancethe resistivity that the material r –the higher the resistivity, the greater its resistance.

resistance = resistivity × length / area

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This equation defines resistivity. We deserve to rearrange it to acquire a formula for resistivity:

resistivity = resistance × area / length

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Question 3
a) Look at the electrode holder in the picture at the optimal of the page. Usage the table to compare the resistivities that copper and steel; use this to define why making use of copper is an energy-efficient choice.

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b) A cable made the a copper alloy is 5m in length and has a cross-sectional area 1mm2. That is resistance is 0.15W. Calculation the resistivity of this alloy.