题目

28.      ----Thomas didn't come to school for the meeting, did he?   ----No. He__ . The meeting had been cancelled. A. shouldn't have come           B. should not come C. didn't need to come           D. wouldn' t have come   答案：C如图所示,真空中有一下表面镀反射膜的平行玻璃砖,其折射率n=．一束单色光与界面成θ=45°角斜射到玻璃砖表面上,最后在玻璃砖的右侧面竖直光屏上出现了两个光点A和B,A和B相距h=2.0 cm．已知光在真空中的传播速度c=3.0×108m/s. 试求:?  ①该单色光在玻璃砖中的传播速度.?  ②玻璃砖的厚度d.