(a) Differentiate between resistance and resistivity (b) the ratio of resistivities of two materials a and b is 1:2, ratio of their length is 3:4 and if the ratio of radii is 2:3 find the ratio of resistance of a and b.

a) Resistance is the obstruction offered to the flow of current by a conductor.
Resistivity is the obstruction offered to the flow of current by UNIT AREA OF the conductor.

So basically, resistance is the property of the object (say a copper wire), whereas resistivity is the property of the substance (copper).

And so resistance depends upon the properties of the object.
Whereas resistivity depends upon the properties of the metal.

So for example take two objects A and B made of aluminium. Both are of a different size.
The resistance of A & B will be different.
But the resistivity will be the same.

 

 

 

So ratio of resitance will be  1 * 3/ (2)² :   2 * 4 / (3)²

 

= 3/4 : 8/9