题目

April 22,2010 will be the 18th celebration of the annual Take Our Daugluers to Work Day （TOD）, a project the National Ms．Foundation for Women of America （NFW） developed to expose girls to expanding opportunities for women in the workplace．        The program offers, millions of girls a first - hand view of the many career opportunities available in their futures．Now that women make up 46 peroent of the U．S．workforce, girls can find role models in every occupational field-from politics to molecular biology to professional athletics, to name just a few．TOD encourages gi用折射率为的透明物质做成内、外径分别为、的球壳，球壳的内表面涂有能完全吸收光的物质，如图所示，当一束平行光从左侧射向该球壳时，被吸收掉的光束在射进球壳左侧外表面前的横截面积有多大？