Aluminium wire has radius 0.25 mm and length or 75 m. If the resistance of the wire is 10Ω, calculate the resistivity of aluminium.
The formula of resistance is: 
Where, 
resistivity
Length of the conductor
A = Area of the conductor
Here:
R = 10
r = 0.25mm
l = 75m
We know that the area of the wire will be: 
Putting the given values in the above formula,
11