题目

通过一个透镜观察印有字母的纸的情形如图所示.由图可知该透镜属于________透镜,所成像的性质是倒立、缩小的________像.纸到透镜的距离是________(填“大于二倍焦距”“大于一倍焦距小于二倍焦距”“等于焦距”或“小于焦距”).此透镜对光线起________(填“会聚”或“发散”)作用. 答案：【答案】凸 实 大于二倍焦距 会聚 【解析】（1）凸透镜对光线有会聚作用，凹透镜对光线有发散作用；（2）凸透镜成像的三种情况：①u＞2f，成倒立、缩小的实像；②2f＞u＞f，成倒立、放大的实像；③u＜f，成正立、放大的虚像。图中透镜成倒立缩小的像，应该是凸透镜的成像情况，u＞2f，成倒立、“Indeed,” George Washington wrote in his diary in 1785, “some kind of fly, or bug, had begun to eat the leaves before I left home.” But the father of America was not the father of bug. When Washington wrote that, Englishmen had been referring to insects as bugs for more than a century, and Americans had already created lightning-bug(萤火虫). But the English were soon to stop using the bugs in their language, leaving it to the Americans to call a bug a bug in the nineteenth and twentieth centuries.        The American bug could also be a person, referring to someone who was crazy about a particular activity. Although fan became the usual term, sports fans used to be called racing bugs, baseball bugs, and the like.        Or the bug could be a small machine or object, for example, a bug-shaped car. The bug could also be a burglar alarm, from which comes the expression to bug, that is, “to install (安装) an alarm”. Now it means a small piece of equipment that people use for listening secretly to others’ conversation. Since the 1840s, to bug has long meant “to cheat”, and since the 1940s it has been annoying.        We also know the bug as a flaw in a computer program or other design. That meaning dates back to the time of Thomas Edison. In 1878 he explained bugs as “little problems and difficulties” that required months of study and labor to overcome in developing a successful product. In 1889 it was recorded that Edison “had been up the two previous nights discovering ‘a bug’ in his invented record player.” 68. We learn from Paragraph 1 that ___________. A.     Americans had difficulty in learning to use the word bug B.      George Washington was the first person to call an insect a bug C.     the word bug was still popularly used in English in the nineteenth century D.     both Englishmen and Americans used the word bug in the eighteenth century 69. What does the word “flaw” in the last paragraph probably mean?        A. Explanation.           B. Finding.           C. Origin.             D. Fault. 70. The passage is mainly concerned with__________. A. the misunderstanding of the word bug  B. the development of the word bug  C. the public views of the word bug          D. the special characteristics of the word bug