Question

Define resistivity of a material. Give its unit.

Answer 1

Hint : In order to solve this question, we need to know the resistivity of the material and it is the property of the material which has the ability to oppose the flow of the current. Since it is the material property so this only depends on the type of material we are using, for the same material there are some aspects in which the material depends; these are length and area of cross-section.

Complete Step By Step Answer:
For solving this question, we should know the term resistance in detail:
Resistance is a measure of the opposition to current flow in an electrical circuit. Resistance is measured in ohms, symbolized by the Greek letter omega $\Omega$. Ohms are named after Georg Simon Ohm (1784-1854), a German physicist who studied the relationship between voltage, current and resistance.
Now we will study the resistivity:
Resistivity, electrical resistance of a conductor of unit cross-sectional area and unit length. A characteristic property of each material, resistivity is useful in comparing various materials on the basis of their ability to conduct electric current. High resistivity designates poor conductors.
The resistance of any conductor is directly proportional to the length of the conductor and inversely proportional to the area of cross-section of the conductor. SI unit of resistivity is ohm-meters.
In terms of formula:
$\rho \propto A$
And
$\rho \propto \dfrac{1}{l}$
After combining both of them:
$\rho \propto \dfrac{A}{l}$
After removal of proportionality constant:
$\rho \propto R\dfrac{A}{l}$
where:
A is area of cross section
l is the length
R is resistance of the material.

Note :
The high resistivity of tungsten are described below:
(i) Hard metal.
(ii) Resistivity twice that of aluminium.
(iii) The thinner the tungsten wire, the greater is its tensile strength.
(iv) In the atmosphere or inert gas or in vacuum, tungsten can be readily worked at temperatures like 2000°C and even higher.
(v) Oxidises very quickly in the presence of oxygen even at a temperature of a few hundred degree centigrade.