The sun is 1.5 X 1011 m from earth. Light produced by the sun travels toward the earth a constant speed of 3 X 108 m/s. If the sun suddenly vanished from the sky, how long would it take for people on earth to see that the sun had disappeared?

Consider the growth of a 20-nm-diameter silicon nanowire onto a silicon wafer. the temperature of the wafer surface is maintained at 2400 k. assume the thermal conductivity of the silicon nanowire is 20 wm-1k-1 and all its surfaces including the tip are subjected to convection heat transfer with the coefficient h = 1×105 wm-2k-1 and t∞ = 8000 k. when the nanowire grows to l = 300 nm, what is the temperature of the nanowire tip (t (x =