Name: resistivity in conductors and insulators
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Resistivity

La resistività elettrica è una proprietà intrinseca di un materiale, che descrive l'efficacia con cui resiste al flusso di cariche.
La resistività è il reciproco della conducibilità elettrica e può essere definita in termini di campo elettrico e densità di corrente. L'unità di misura della resistività è l'ohmmetro.
I buoni conduttori hanno un'alta conduttività ma una bassa resistività, mentre i buoni isolanti hanno una bassa conducibilità ma un'alta resistività.
La temperatura influenza la resistività di alcuni materiali. In molti materiali, la dipendenza è approssimativamente lineare e può essere modellata utilizzando un'equazione lineare dove ρ è la resistività del materiale a una temperatura, α è il coefficiente di temperatura del materiale e ρ0 è la resistività a temperatura ambiente.
La resistività di alcuni materiali, come il rame, aumenta all'aumentare della temperatura; in altri, come il carbonio, la resistività diminuisce all'aumentare della temperatura.
Nei semiconduttori, il coefficiente di temperatura è negativo, il che implica che la resistività diminuisce all'aumentare della temperatura.

<ol>
	<li>OpenStax. (2019). Fisica universitaria Vol. 2. [Versione web], Pg 396 - 398. Estratto da <a href="https://openstax.org/books/university-physics-volume-2/pages/9-3-resistivity-and-resistance">https://openstax.org/books/university-physics-volume-2/pages/9-3-resistivity-and-resistance</a></li>
</ol>

resistività

Quando viene applicata una tensione a un conduttore, si genera un campo elettrico, e le cariche nel conduttore avvertono la forza dovuta al campo elettrico. La densità di corrente che ne risulta dipende dal campo elettrico e dalle proprietà del materiale. In alcuni materiali, tra cui i metalli a una data temperatura, la densità di corrente è approssimativamente proporzionale al campo elettrico. In questi casi, la densità di corrente può essere modellata come:

<img alt="Equation1" src="/files/ftp_upload/13746/13746_Equation_1.svg" style="text-align: center; height: 16px;" />

dove σ è la conducibilità elettrica ed è rappresentata da (Ω⋅m)−1. La conducibilità elettrica è analoga alla conducibilità termica ed è una misura della capacità di un materiale di condurre o trasmettere l'elettricità. I conduttori hanno una maggiore conducibilità elettrica rispetto agli isolanti. La conducibilità è una proprietà intrinseca di un materiale. Un'altra proprietà intrinseca di un materiale è la sua resistività, o resistività elettrica. La resistività di un materiale è una misura di quanto fortemente un materiale si oppone al flusso di corrente elettrica. La resistività può essere definita come il reciproco della conducibilità elettrica ed è rappresentata dalla lettera greca rho, ρ. L'unità di resistività nelle unità SI è l'ohm-metro. La resistività può anche essere definita come il rapporto tra il campo elettrico e la densità di corrente. Maggiore è la resistività, maggiore è il campo necessario per produrre una data densità di corrente. Più bassa è la resistività, maggiore è la densità di corrente prodotta da un dato campo elettrico. Come indicato nella Tabella 1, i buoni conduttori mostrano una elevata conducibilità e una bassa resistività, mentre i buoni isolanti mostrano una bassa conducibilità e una elevata resistività.

Table 1: Elenco dei valori di resistività e conducibilità per vari materiali.

<table style="margin-left: auto; margin-right: auto;">
	<tbody style="border: 1px solid black;">
		<tr>
			<td style="color: black; border: 1px solid black; text-align: center;">Materiali</td>
			<td style="color: black; border: 1px solid black; text-align: center;">Conducibilità, σ 
			( Ω · m)−1</td>
			<td style="color: black; border: 1px solid black; text-align: center;">Resistività, ρ 
			( Ω · m)</td>
			<td style="color: black; border: 1px solid black; text-align: center;">Temperatura 
			Coefficient, α (°C)−1</td>
		</tr>
		<tr>
			<td style="color: black; border: 1px solid black; text-align: center;">Silver</td>
			<td style="color: black; border: 1px solid black; text-align: center;">6.29 × 107</td>
			<td style="color: black; border: 1px solid black; text-align: center;">1.59 × 10−8</td>
			<td style="color: black; border: 1px solid black; text-align: center;">0.0038</td>
		</tr>
		<tr>
			<td style="color: black; border: 1px solid black; text-align: center;">Copper</td>
			<td style="color: black; border: 1px solid black; text-align: center;">5.95 × 107</td>
			<td style="color: black; border: 1px solid black; text-align: center;">1.68 × 10−8</td>
			<td style="color: black; border: 1px solid black; text-align: center;">0.0039</td>
		</tr>
		<tr>
			<td style="color: black; border: 1px solid black; text-align: center;">Gold</td>
			<td style="color: black; border: 1px solid black; text-align: center;">4.10 × 107</td>
			<td style="color: black; border: 1px solid black; text-align: center;">2.44 × 10−8</td>
			<td style="color: black; border: 1px solid black; text-align: center;">0.0034</td>
		</tr>
		<tr>
			<td style="color: black; border: 1px solid black; text-align: center;">Aluminum</td>
			<td style="color: black; border: 1px solid black; text-align: center;">3.77 × 107</td>
			<td style="color: black; border: 1px solid black; text-align: center;">2.65 × 10−8</td>
			<td style="color: black; border: 1px solid black; text-align: center;">0.0039</td>
		</tr>
		<tr>
			<td style="color: black; border: 1px solid black; text-align: center;">Tungsten</td>
			<td style="color: black; border: 1px solid black; text-align: center;">1.79 × 107</td>
			<td style="color: black; border: 1px solid black; text-align: center;">5.60 × 10−8</td>
			<td style="color: black; border: 1px solid black; text-align: center;">0.0045</td>
		</tr>
		<tr>
			<td style="color: black; border: 1px solid black; text-align: center;">Carbon (pure)</td>
			<td style="color: black; border: 1px solid black; text-align: center;">2.86 × 10−6 </td>
			<td style="color: black; border: 1px solid black; text-align: center;">3.50 × 10−5 </td>
			<td style="color: black; border: 1px solid black; text-align: center;">−0.0005</td>
		</tr>
		<tr>
			<td style="color: black; border: 1px solid black; text-align: center;">Silicon</td>
			<td style="color: black; border: 1px solid black; text-align: center;"></td>
			<td style="color: black; border: 1px solid black; text-align: center;"> 0.1 − 2300</td>
			<td style="color: black; border: 1px solid black; text-align: center;">−0.07</td>
		</tr>
		<tr>
			<td style="color: black; border: 1px solid black; text-align: center;">Amber</td>
			<td style="color: black; border: 1px solid black; text-align: center;">2.00 × 10−15 </td>
			<td style="color: black; border: 1px solid black; text-align: center;">5 × 1014</td>
			<td style="color: black; border: 1px solid black; text-align: center;"></td>
		</tr>
		<tr>
			<td style="color: black; border: 1px solid black; text-align: center;">Glass</td>
			<td style="color: black; border: 1px solid black; text-align: center;">10−9 − 10−14</td>
			<td style="color: black; border: 1px solid black; text-align: center;">109 − 1014</td>
			<td style="color: black; border: 1px solid black; text-align: center;"></td>
		</tr>
		<tr>
			<td style="color: black; border: 1px solid black; text-align: center;">Lucite</td>
			<td style="color: black; border: 1px solid black; text-align: center;"><10−13 </td>
			<td style="color: black; border: 1px solid black; text-align: center;">>1013</td>
			<td style="color: black; border: 1px solid black; text-align: center;"></td>
		</tr>
	</tbody>
</table>

Resistività

Quando viene applicata una tensione a un conduttore, viene generato un campo elettrico e le cariche nel conduttore sentono la forza dovuta al campo elettrico. Le...

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resistivity in conductors and insulators

Resistivity describes how much a material opposes electric current. When a voltage is applied to a conductor, an electric field forms. The charges in the conductor feel that force, and a current density develops. In some materials, including metals at a given temperature, the current density is approximately proportional to the electric field.

In those cases, current density can be modeled with conductivity, written as sigma. Electrical conductivity is measured in (ohm·m)^−1. It tells how well a material can conduct electricity. This idea is similar to thermal conductivity, which describes how well a material carries heat. Conductors have higher electrical conductivity than insulators, and conductivity is an intrinsic property of the material.

Resistivity, written as rho, is another intrinsic property. It is the reciprocal of electrical conductivity. In SI units, resistivity is measured in ohm-meter. It can also be defined as the ratio of electric field to current density. A higher resistivity means a larger electric field is needed to produce a given current density. A lower resistivity means the same electric field produces a larger current density.

The transcript also compares common materials. Good conductors have high conductivity and low resistivity. Good insulators have low conductivity and high resistivity. Examples of good conductors include silver, copper, gold, aluminum, and tungsten. Pure carbon has much lower conductivity than these metals. Silicon falls between conductor and insulator values, while amber, glass, and Lucite show very high resistivity and very low conductivity.

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Resistivity in Conductors and Insulators

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