You are watching: What does the resistivity of a wire depend on?
|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.
|Picture 2.2 Graph the resistivities of part metals.|
|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.|
|Picture 2.3 Graphics to illustrate how resistance varies v l, A and rho.|
|To calculation the resistance R the a wire, we need to understand three things:its size |
the much longer the wire, the higher its resistanceits cross-sectional area Athe 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
This equation defines resistivity. We deserve to rearrange it to acquire a formula for resistivity:
resistivity = resistance × area / length
|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.