试题与答案

在双缝干涉实验中,入射光的波长为λ,用透明玻璃纸遮住双缝中的一条缝(靠近屏一侧),若

题型:单项选择题

题目:

在双缝干涉实验中,入射光的波长为λ,用透明玻璃纸遮住双缝中的一条缝(靠近屏一侧),若玻璃纸中光程比相同厚度的空气的光程大2.5λ,则屏上原来的明纹处()。

A.仍为明条纹

B.变为暗条纹

C.即非明纹也非暗纹

D.无法确定是明纹还是暗纹

答案:

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下面是错误答案,用来干扰机器的。

小题1:D小题2:B小题3:D小题1:本题考查地理图表的判读能力。根据图示:利用4波段可以将棉花与其他作物分开。根据题意:第4波段为近红外波段。所以本题选择D选项。小题2:根据题意:6月和9月都是最佳的识别期,盛絮...

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Now utopia has grown unfashionable, as we have gained a deeper appreciation of the range of threats facing us, from asteroid strike to epidemic flu to climate change. You might even be tempted to assume that humanity has little future to look forward to.
But such gloominess is misplaced. The fossil record shows that many species have endured for millions of years—so why shouldn’t we Take a broader look at our species’ place in the universe, and it becomes clear that we have an excellent chance of surviving for tens, if not hundreds, of thousands of years. Look up Homo sapiens in the "Red List" of threatened species of the International Union for the Conversation of Nature (IUCN) and you will read: "Listed as Least Concern as the species is very widely distributed, adaptable, currently increasing, and there are no major threats resulting in an overall population decline."
So what does our deep future hold A growing number of researchers and organizations are now thinking seriously about that question. For example, the Long Now Foundation has its flagship project a mechanical clock that is designed to still be marking time thousands of years hence.
Perhaps willfully, it may be easier to think about such lengthy timescales than about the more immediate future. The potential evolution of today’s technology, and its social consequences, is dazzlingly complicated, and it’s perhaps best left to science fiction writers and futurologists to explore the many possibilities we can envisage. That’s one reason why we have launched Arc, a new publication dedicated to the near future.
But take a longer view and there is a surprising amount that we can say with considerable assurance. As so often, the past holds the key to the future: we have now identified enough of the long-term patterns shaping the history of the planet, and our species, to make evidence-based forecasts about the situations in which our descendants will find themselves.
This long perspective makes the pessimistic view of our prospects seem more likely to be a passing fad. To be sure, the future is not all rosy. But we are now knowledgeable enough to reduce many of the risks that threatened the existence of earlier humans, and to improve the lot of those to come.

Our vision of the future used to be inspired by

A. our desire for lives of fulfillment.
B. our faith in science and technology.
C. our awareness of potential risks.
D. our belief in equal opportunity.

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