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When a collection of two-level systems is in equilibrium at temperature T, , the ratio of
the population in the lower and upper levels is 2:1. When the temperature is changed to
T, the ratio is 8:1. Then
(a) T = 2T,
(b) Т, — 27
(с) Т, %3 3Т
(d) T, = 4T

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