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问题 计算题

如图所示，一段横截面为正方形的玻璃棒，中间部分弯成四分之一圆弧形状，一细束单色光由MN端面的中点垂直射入，恰好能在弧面EF上发生全反射，然后垂直PQ端面射出。

（1）求该玻璃棒的折射率，

（2）若将入射光向N端平移，当第一次射到弧面EF上时____（填“能”“不 能”或“无法确定能否”）发生全反射。

答案

解：（1）如图所示单色光照射到EF弧面上时刚好发生全反射，

由全反射的条件得C=450①

由折射定律得②

联立①②得

（2）能。

单项选择题 A1型题

关于IUD取出的时间选择，下列哪项正确（）

A.月经干净后3～7日无性生活取器为宜

B.子宫出血者必须完全止血后取器

C.带器妊娠必须先取器再流产

D.带器异位妊娠者术后3次月经后取器

E.以上均正确
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单项选择题

The development of e-commerce may well bring the world into a brand new era of "electronic currency". At the moment, (51) areas in Europe, the United States and Asia have already started studying the possibility of an electronic currency. Electronic currency is not only about currency. It (52) to an entire finance system on the Net. It includes a virtual numeric currency, an electronic system of withdrawals, transfers and loans, and (53) cards of all shapes and sizes. The (54) of an electronic currency system implies the emergence of "virtual banks" and "virtual enterprises". Actually, the first virtual bank appeared in the US in 1995. (55) it is a small and insignificant bank, it represents the trend of the future. In time to come, we may even have to (56) the familiar paper currency.

As the Net pushes the economy (57) rapidly, the economy is also bringing the Net market forward, resulting in the Internet itself becoming the world’s largest emerging market. Of course, this is just the beginning. Although there are many companies which made huge profits (58) in the Internet market, they tend to be small companies. To date, most companies are making losses. The competition in the knowledge-based economy will also be more (59) This will definitely promote (60) and more efficient cooperation.

51().

A.developing 

B.building 

C.built 

D.developed
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