Chapter 12, Problem 12.60P

Radiation leaves a furnace of inside surface temperature 1500 K through an aperture 20 mm in diameter. A portion of the radiation is intercepted by a detector that is 1 m from the aperture, has a surface area of ${10}^{-5}{m}^2$ , and is oriented as shown.

If the aperture is open, what is the rate at which radiation leaving the furnace is intercepted by the detector? If the aperture is covered with a diffuse, semitransparent material of spectral transmissivity ${\tau }_{\lambda }=0.8\text{ for}\lambda \le 2\mu m\text{ and }{\tau }_{\lambda }=0\text{ for }\lambda \text{>2}\mu \text{m}$ , what is the rateat which radiation leaving the furnace is intercepted by the detector?