GATE 2021 MT – Question 65
A solid sphere of radius 0.5 m is enclosed by a hollow sphere of radius 1 m. Radiation exchanges between the small sphere’s outer surface (1) and large sphere’s inner surface (2). View factor $F_{ij}$ is the fraction of radiation leaving i intercepted by j. The value of $F_{22}$ is ______ (two decimal places).
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Correct answer: 0.74 to 0.76
Explanation
The inner convex sphere sees only the outer sphere, so F12=1. Reciprocity gives F21=A1/A2=(0.5/1)²=0.25. The outer surface enclosure sum is F21+F22=1, yielding **F22=0.75**.