In a tempering process, glass plate, which is initially at a uniform temperature Ti, is cooled by suddenly reducing the temperature of both surfaces to Ts. The plate is 20 mm thick, and the glass has a thermal diffusivity of 6 x 10-7 m2/s.
(a) How long will it take for the mid plane temperature to achieve 50% of its maximum possible temperature reduction?
(b) If (Ti - Ts) = 300°e, what is the maximum temperature gradient in the glass at the above time?