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According to Stefan's law, radiation power is proportional to the 4th power of absolute temperature. Then: P1 : T1^4 = P2 : T2^4 P2 = P1 (T2/T1)^4 = 40 x (2400/2050)^4 = 40 x 1.17^4 = 75w Answer D is the correct one
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