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The thermal conductivity of a material is to be determined by fabricating the material into the shape of a hollow sphere, placing an electric heater at the centre and measuring the surface temperatures with thermocouples when steady state conditions have been attained. The sphere has internal radius 3cm, external radius 8cm and the corresponding temperatures are 95C and 85C when an electrical input to heater is 10W. Determine the experimental value of thermal conductivity and the temperature at a point halfway through the wall