问题 问答题 简答题

为什么直流不能通过电容器而交流电能通过电容器?

答案

参考答案:

因为电容器的电流与电容器两端电压的变化率成正比。直流电路中,当电路充电过程结束后,电容两端的电压与电源的直流电压相等,不再变化,即电压的变化率为零,则电流也为零。交流电路中,由于电压的变化率不为零,则电流也不为零。所以说电容器能隔直通交。

阅读理解

For a long time, humans have used technology (科技) to study the world around us, and Mars is the latest place we’re using machines to explore. Besides the earth, the “red planet” is seen, as the one place in our solar system most likely to have life.

Early last month, the first American robot, Spirit, landed on Mars without any problem. Opportunity, the second robot, landed on the planet more than a week ago. Scientists are very excited about these machines’ safe landing on Mars. It means that now we have an excellent chance to look for water and other signs of life. So far, the robots have found some stones that could show Mars was once a wet and warm planet.

But the trips made by Spirit and Opportunity were dangerous. Mars is often called the “death planet”, because in the past its environment has been unfriendly to the robot explorers. Before Spirit and Opportunity, nearly forty spaceships had been sent to Mars since the 1960s. Two-thirds of them failed. The first spaceship, Korabl, sent in 1962 by Russia was among them. It broke apart (分裂) near the earth.

小题1:For a long time humans think ________.

A.they can surely find life on Mars

B.there may be life on Mars

C.it’s too late for them to explore Mars now

D.Mars is the only planet that has life on it小题2:The two robots ________.

A.have found out that it is warm and wet on Mars

B.were sent to Mars to find some stones

C.were the first two American robots that landed on Mars

D.are the only machines that have landed on Mars so far小题3:The third paragraph mainly tell us ________.

A.it’s a very hard and dangerous trip for spaceships to Mars

B.two-thirds of the spaceships sent to Mars have failed

C.Spirit and Opportunity landed on Mars successful

D.Mars is called the “death planet”小题4:From this passage we learn that ________.

A.the two robots have found water on Mars

B.Opportunity touched on Mars a week later than Spirit

C.it’s exciting to have the chance to look for signs of life on Mars

D.Korabl was the first Russian machine to land on Mars

问答题 简答题