1. The problem statement, all variables and given/known data Black-body radiation, at temperature Ti fills a volume V. The system expands adiabatically and reversibly to a volume 8V. The final temperature T_f = xT_i, where the factor x is equal to (a) 0.5 (b) 2.8 (c) 0.25 (d) 1 2. Relevant equations 3. The attempt at a solution Correct answer should be (d)1 because, photons do not feel attraction or repulsion potential to each other.So, increasing volume adiabatically should not reduce or increase its temperature. Please check if I am correct.