LEARNATHON
III

Competition for grade 6 to 10 students! Learn, solve tests and earn prizes!

Theory:

The property of a material that helps the movement of charges and thus the current flow in the circuit is known as Conductance. It is denoted as $$G$$.
Mathematically, it is defined as the reciprocal of its resistance ($$R$$).

The formula of conductance '$$G$$' is given by

The SI unit of conductance of a material is $$ohm^{–1}$$ (or) $$mho$$ (or) $$siemen$$.

Conductivity:
Electrical conductivity is the reciprocal of the electrical resistivity of a material. The SI unit is $$ohm^{–1}\ metre{–1}$$ (or) $$mho\ metre{–1}$$ (or) $$siemen\ metre{–1}$$.
The formula of conductivity is given by

$\mathrm{\sigma } =\phantom{\rule{0.147em}{0ex}}\frac{1}{\mathrm{\rho }}$
Electrical conductivity is a material's ability to pass the current through it.
The conductivity of conductors is higher than that of insulators. However, the resistivity of conductors is lesser than that of insulators.

Like resistivity, conductivity is also constant for a material. The resistivity of some common materials at $$20\ °C$$ are shown in the table below.

 Material's nature Material Resistivity of material ($$\Omega\ m$$) Conductors Silver  Copper Aluminium Tungsten Nickel Iron Chromium  Mercury  Manganese $$1.60\times{10^{-8}}$$ $$1.62\times{10^{-8}}$$ $$2.63\times{10^{-8}}$$ $$5.20\times{10^{-8}}$$ $$6.84\times{10^{-8}}$$ $$10.0\times{10^{-8}}$$ $$12.9\times{10^{-8}}$$ $$94.0\times{10^{-8}}$$ $$1.84\times{10^{-6}}$$ Alloys Constantan  Manganin  Nichrome $$49\times{10^{-6}}$$ $$44\times{10^{-6}}$$ $$100\times{10^{-6}}$$ Insulators Glass Hard rubber  Ebonite  Diamond Dry paper $$10^{10}$$ to $$10^{14}$$ $$10^{13}$$ to $$10^{16}$$ $$10^{15}$$ to $$10^{17}$$ $$10^{12}$$ to $$10^{13}$$ $$10^{12}$$

What is an alloy?
An alloy is a mixture of two or more metals or elements.
Example:
Constantan is an alloy of copper (Cu) and nickel (Ni).
Manganin is an alloy of copper (Cu), manganese (Mn) and nickel (Ni).
Nichrome is an alloy of nickel (Ni), chromium (Cr), manganese (Mn) and iron (Fe).
From the above table, it is clear that the resistivity of an alloy is higher than that of metals. At higher temperatures, alloys do not oxidise or burn easily. Hence, alloys are used in electrical heating devices, like electric iron, toasters, heaters, etc.

Alloys inside electric iron box

Tungsten, an alloy of nickel and copper or nickel and iron, is commonly used as a filament in electric bulbs. Whereas, the metals like copper and aluminium are used for electrical transmission lines.

Tungsten in light bulb