A hollow sphere of inner radius r1 = 30 cm and outer radius r2 = 50 cm is heated at the inner surface. The temperature a

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A hollow sphere of inner radius r1 = 30 cm and outer radius r2 =
50 cm is heated at the inner surface. The temperature at the inside
and outside surfaces of the sphere is T1 and T2. The thermal
conductivity of the material is k = 170 W.(m.K)-1 . (a) Demonstrate
that the rate of heat conduction is computed by the formula: 1 2 1
2 2 1 4 T T P kr r r r     . (b) The difference of temperature
between two surfaces of the sphere is 7.0oC. Find the rate of heat
flow out of the sphere.