Let us try to define what conductivity of a material is
Whenever we apply voltage across a conductor, there will be current flowing through that
But for the same voltage, this current will not be same for all conductors of same dimension
That means, if you use an aluminum conductor and measure the current through it, and then
you use a copper conductor of same dimension, that is of same length and cross section
and measure the current through it, you will find the current in copper conductor is more
than that of aluminum conductor for same applied voltage. This is because current carrying capability of copper is more than that of aluminum
Again, if we do the same observation by using same dimensional conductors of different materials
we will find different currents flowing through them for same applied voltage
From these observations, we can conclude that current carrying capability of different materials
are different. This current carrying capability of a particular material is measured in terms of conductivity
of that material. And conductivity is defined as the inducement offered by the conductor to the flow of current
and is measured in Siemens per meter. By this explanation, it is quite clear that, conductivity of material is opposite property
of resistivity. We know that, by resistivity, we measure how a material resists the flow of current through it
Hence, mathematically conductivity is the reciprocal of resistivity. Conductivity of a material is denoted as rho, and conductivity of the material is generally
denoted as lambda, and it is equal to 1 by rho. This was all about conductivity of a material
Now we will try to understand what is conductance of a conductor
The reciprocal of resistance, that is 1 by R is called conductance, and is denoted by
English letter G. The unit of conductance is mho
Now in modern engineering, the unit is denoted as Siemens, although mho and Siemens are same
that is 1 Siemens equal to 1 mho. Thank you