题干

入射光照射到某金属表面上发生光电效应,若入射光的强度减弱,而频率保持不变,那么(  )

A:从光照至金属表面上到发射出光电子之间的时间间隔将明显增加

B:逸出的光电子的最大初动能将减小

C:单位时间内从金属表面逸出的光电子数目将减少

D:有可能不发生光电效应

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答案(点此获取答案解析)

C

同类题3

阅读理解

    As has been all too apparent in recent days at Balcombe, few issues cause greater concern than energy policy. Many village communities feel their countryside is being ruined by the power-producing machines of wind farms; yet they never take “ direct action”, even though the planning laws put them at a severe disadvantage. And the generous subsidies(财政补贴),which encourage the expansion of wind power, are not favorable to the village communities and set landowners in conflict with other residents.

    Those who disagree with the rapid expansion of wind farms state that the damage they cause is out of proportion to the benefits they bring, because their energy output cannot match that of the carbon-based power stations they are supposed to replace. Supporters insist that wind must be part of a mix of renewables, nuclear and carbon, and that the country is committed to meeting EU(European Union) targets for non-carbon energy generation.

    Against this background, the fact that there is an argument within the Government over whether to publish an official report on wind farms impact on the countryside becomes even more extraordinary. The two parties in the coalition government are in disagreement over what it should say.

    We have some advice for the two parties :publish the report ,and let the country be the judge. Even if it contains evidence that wind farms are harmful, it will hardly be a pleasant surprise to people who do not like them. Equally, supporters must argue their case by acknowledging the concerns and explaining why they are either misplaced or worthy of much attention.

    The suggestion that further negotiations are to take place to produce an “acceptable” report suggests that the politics of coalition government are doing the country harm in a certain way. Given the sensitivities involved ,all the information should be available so that people can reach their own conclusions, rather than being left with the suspicion that facts are being replaced by political beliefs.

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