本刊 2 0 0 4年第 1期《几何光学中的“玻璃体问题”举隅》一文中的例题 2如下 :图 7例题 .用折射率为n的玻璃做成内外半径分别为a、b的空心球 ,如图 1所示 .球的内表面涂有完全吸收光的物质 .当一束平行光射向此球时 ,球吸收的平行光束的横截面图 1积多大 ?解析 :本题综合考查 The example 2 of the “vitreous glass problem” in Geometry Optics, 2004 is as follows: Fig. 7 Example. Using glass with refractive index n to make inner and outer radii respectively a and b Hollow ball, as shown in Figure 1. The inner surface of the ball is coated with a substance that completely absorbs light. When a beam of parallel light hits the ball, the cross-section of the parallel beam absorbed by the ball shows how big is the product. Analysis: This topic is a comprehensive examination.