Heat flow across a hollow sphere of inner radius ‘r1’ and outer radius ‘r2’ is directly proportional to__________________? October 19, 2020 by Admin A. (r2 – r1)/r1. r2B. r1. r2/(r2 – r1) C. (r2 + r1)/r1. r2 D. r1. r2/(r2 + r1)
