CBSE Class 10 Answered

In this type of problem, we must divide the object whose resistance we are calculating into concentric elements of infinitesimal thickness dr. We start by using the differential form of replacing r for the distance variable: , where dR is the resistance of the element of thicknessdr and surface area A.In this example, we take as our representative concentric elements a hollow cylinder of pipe of length L=1m.Any current passes from inner conductor to outer one must past radially through the concentric elements, and the area  through which the current passes as A=2L (This is the curved surface area -circumference multiplied by length of our hollow cylinder of thickness dr). Hence the required resistance is