问题 选择题

如图所示是光电管的原理图,已知当有波长为λ0的光照到阴极K时,电路中有光电流,则(   )

A.若换用波长为λ1(λ1>λ0)的光照射阴极K 时,电路一定没有光电流

B.若换用波长为λ2(λ2<λ0) 的光照射阴极K时,电路中光电流一定增大

C.若将变阻器滑动头P从图示位置向右滑一些,仍用波长λ0的光照射,则电路中光电流一定增大

D.若将变阻器滑动头P从图示位置向左滑过中心O点时,其他条件不变,则电路中仍可能有光电流

答案

AD

题目分析:用波长为λ的光照射阴极K时,电路中有光电流,知波长为λ的光照射阴极K时,发生了光电效应.换用波长为λ1(λ1>λ)的光照射阴极K时,由于频率变小,一定不发生光电效应,电路中一定不有光电流.故A正确.换用波长为λ2(λ2<λ)的光照射阴极K时,频率变大,一定能发生光电效应,电路中一定有光电流.故B错误.滑动变阻器滑头P向右滑动增大,如果滑动前达到饱和电流,那么滑动后电流不再增大,C错误;若滑动头左滑,是反向电压,只要不超过反向遏制电压,就有光电流,故D正确;

故选AD

点评:解决本题的关键掌握光电效应的条件,当入射光的频率大于截止频率,就会发生光电效应.

单项选择题
填空题

For centuries people have been fighting over whether governments should allow trade between countries. There have been, and probably always will be, (1) to the argument. Some people argue that just (2) is best for both the country and the world. Others argue that trade with other countries (3) for some people to make a good living. Both sides are at least (4) .
International trade matters a lot. Its effects on (5) are enormous. Imagine a world in which your country (6) at all with other countries. Imagine what kind of job you would be (7) and what goods you could buy or not buy in such a world.
For the United States, for example, start by imagining that it lived without its (8) a year in imported oil, and cut back on its (9) because the remaining domestic oil and other energy sources were (10) . Producers and consumers in other parts of the economy would (11) if they were suddenly stripped of foreign-made goods like CD players and clothing. On the (12) side, suppose that Boeing could sell airplanes, and farmers could sell their crops, (13) the United States, and that U. S. universities could admit only (14) . In each case there are people who gain and people who lose from (15) international trade. In any case, less or more international trade will have (16) on your career as well as your life.
For years, American companies are often faced with the choice of buying (17) , which are expensive, and foreign-made goods, which are cheap. If the company buys American goods, it may (18) taxpayers by failing to keep prices low. But if it buys foreign goods, it may (19) the jobs of American workers. Recently, Congress has passed a law compelling American companies with government contracts to (20) domestic goods and services.

For centuries people have been fighting over whether governments should allow trade between countries. There have been, and probably always will be, (1) to the argument. Some people argue that just (2) is best for both the country and the world. Others argue that trade with other countries (3) for some people to make a good living. Both sides are at least (4) .
International trade matters a lot. Its effects on (5) are enormous. Imagine a world in which your country (6) at all with other countries. Imagine what kind of job you would be (7) and what goods you could buy or not buy in such a world.
For the United States, for example, start by imagining that it lived without its (8) a year in imported oil, and cut back on its (9) because the remaining domestic oil and other energy sources were (10) . Producers and consumers in other parts of the economy would (11) if they were suddenly stripped of foreign-made goods like CD players and clothing. On the (12) side, suppose that Boeing could sell airplanes, and farmers could sell their crops, (13) the United States, and that U. S. universities could admit only (14) . In each case there are people who gain and people who lose from (15) international trade. In any case, less or more international trade will have (16) on your career as well as your life.
For years, American companies are often faced with the choice of buying (17) , which are expensive, and foreign-made goods, which are cheap. If the company buys American goods, it may (18) taxpayers by failing to keep prices low. But if it buys foreign goods, it may (19) the jobs of American workers. Recently, Congress has passed a law compelling American companies with government contracts to (20) domestic goods and services.