There are two concentric spheres of radius (a) and (b) respectively. If the space between them is filled with medium of resistivity `rho`, then the resistance of the intergap between the two spheres will be

Explanation

Consider a cocentric spherical shell of radius x and thickness dx, its resistance is dR,
`dR=(rho dx)/(4pix^(2))`
Total resistance `R=int_(a)^(b)dR=R=((rho)/(4pi))int_(a)^(b)(dx)/(x^(2))=(rho)/(4pi)[(1)/(a)-(1)/(b)]`