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

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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 rate of heat flow out
of the sphere is 11.30 kW. 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) Find the difference of temperature between two surfaces of
the sphere.