Two thin metallic spherical shells of radii `r_(1)` and `r_(2)` `(r_(1)lt r_(2))` are placed with their centres coinciding. A material of thermal conductivity `K` is filled in the space between the shells. The inner shells is maintained at temperature `theta_(1)` and the outer shell at temperature `theta_(2)` `(theta_(1)lttheta_(2))`. Calculate the rate at which heat flows radially through the material.

Options

A. `(R_(1)+R_(2))/(2)`
B. `(R_(1)R_(2))/(R_(1)+R_(2))`
C. `(2R_(1)R_(2))/(R_(1)+R_(2))`
D. `R_(2)-R_(1)`

Answer

C