Two thin metallic spherical shells of radii r₁ and r₂ (r₁ < r₂) are placed with their centres coinciding. A material of thermal conductivity K is filled in the space between the shells. The inner shell is maintained at temperature 0₁ and the outer shell at temperature 0₂(0₁<0₂). The rate at which heat flows radially through the material is :-

Two thin metallic spherical shells of radii r₁ and r₂ (r₁ < r₂) are placed with their centres coinciding. A material of thermal conductivity K is filled in the space between the shells. The inner shell is maintained at temperature 0₁ and the outer shell at temperature 0₂(0₁<0₂). The rate at which heat flows radially through the material is :-