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Chapter 19 - 19.8

8. From ∆ T =∆ T 0 e − At ,wehave∆ T/ ∆ T 0 = e − A 1 t 1

(before insulation) and ∆ T/ ∆ T 0 = e − A 2 t 2

(after

insulation). Thus the ratio is given by A 2 /A 1 = t 1 /t 2 =1 / 2.