A Ge-Ga crystal is grown by normal freezing. Initial melt composition is 10 ppm Ga. Growth rate is 8 x 10^(-3) cm/s. (a) If convection is completely absent, what thermal gradient is required to maintain a plane front when the ingot is 50 percent solidified? (b) If convection is sufficiently vigorous that K^' ≅ K, what thermal gradient is required to maintain a plane front when the ingot is 50 percent solidified? (c) If 0 = 0.005 cm, what thermal gradient is required to maintain a plane front when the ingot is 50 percent solidified?