A hollow metallic sphere of radius `20cm` surrounds a concentric metallic sphere of radius `5cm`. The space between the two sphere is filled with a nonmetallic material. The inner and outer sphere are maintained at `50^(@)C` and `10^(@)C` respectively and it is found that `100J` of heat passes from the inner sphere to the outer sphere per second. Find the thermal conductivity of the material between the sphere.
