Two long coaxial and conducting cylinders of radius a and b are separated by a material of conductivity σ and a constant potential difference V is maintained between them, by a battery. Then the current, per unit length of the cylinder following from one cylinder the other is:
I=I/A=σE.
E=I2πσL1s^r.
V=∫baE⋅ds=∫ba(I2πσL)1sds.
=I2πσLln(b/a)
I=(2πσL)Vln(b/a)