A hollow pure copper sphere with an electrical heater in the center is used in tests at steady-state conditions to determine the thermal conductivity of insulating materials. The inner diameter of the sphere is 0.250m; the outer diameter is 0.300m. For this test, the inner temperature of the pure copper sphere is held at a constant temperature of 225.0°C. The pure copper sphere is uniformly covered with an insulating material, 0.0800m thick. The outside of the insulating material is exposed to convection ; Too 25.0°C, h = 22.0 W/ (m2-K). The powe r required to keep the inner surface of the sphere at 2250°C is 75.0W (this is then equal to the heat transfer rate, g). Ignoring contact resistance, determine the thermal conductivity of the insulating material, k.