l>Copper and electricity. Resistance and 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 that copper renders it perfect for this electrode holder i beg your pardon carries huge currents to a stole making arc furnace.

When we say the copper is a heavier steel than aluminium, we room comparing their densities. In a similar way, as soon as we say the copper is a better conductor than aluminium, we space comparing your resistivities.

Density and resistivity room both bulk properties the a material. Their value doesn\"t count on the size or shape of a particular sample – only on the product itself.

Resistivity: relies on the product onlyResistance: counts on size and shape - and also on the material.

What is resistivity?
In effect, the resistivity to represent the resistance across two opposite faces of a cubic metre of product (in the same way that density is the mass of a cubic metre). Resistivity tells just how resistive a material is.

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

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Picture 2.2 Graph that resistivities of some metals.
Some resistivities
Table 3 shows some resistivities. Girlfriend will watch that resistivity different from around 10-8Wm to much more than 1016Wm – more than 24 order of magnitude. No various other property of materials varies over such a wide range.
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Picture 2.3 Graphics come illustrate how resistance varies through l, A and also rho.
Calculating resistance
To calculate the resistance R the a wire, we require to recognize three things:its length
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–the longer the wire, the greater its resistanceits cross-sectional area A–the greater the area, the less its resistancethe resistivity that the material r –the higher the resistivity, the higher its resistance.

resistance = resistivity × size / area

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This equation specifies resistivity. We can rearrange it to gain a formula for resistivity:

resistivity = resistance × area / size

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Question 3
a) Look at the electrode holder in the photograph at the top of the page. Use the table to to compare the resistivities that copper and also steel; usage this to describe why utilizing copper is an energy-efficient choice.

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