A billet of steel 30.5 cm in diameter,61 cm long, initially at 645 K, is immersed in an oil bath that is maintained at 310 K. if the surface conductance is 34W/m2'K determine the center temperature of the billet after 1 h.

The horizontal blue line through the middle of the lens is called the optical axis. as the lamp is moved above or below the axis, keeping the horizontal distance to the center of the lens constant, how does the horizontal distance from the lens to the image change?