A fused-quartz sphere has a thermal diffusivity of 9.5 × 10−7 m2/s, a diameter of 2.5 cm, and a thermal conductivity of 1.52 W/m· ºC. The sphere is initially at a uniform temperature of 25ºC and is suddenly subjected to a convection environment at 200ºC. The convection heat-transfer coefficient is 110 W/m2 · ºC. Calculate the temperatures at the center and at a radius of 6.4 mm after a time of 3 min.