A hollow cylinder of specific resistance `rho`, inner radius R, outer radius 2R and length l is as shown in figure. What is the net resistance between the inner and outer surface?

Explanation

Consider a ring of width .dr. and radius .r..
Resistance across
the ring is `dR=(rhodr)/(dA)=(rhodr)/(2pi rl)`

Net resistance `=int_(R)^(2R)(rho(dr))/((2pirl))=((rho)/(2pil))ln(2)`