电路中C是平行板电容器，S先触1后又扳到2，若这时将平行板的板间距拉大一点，下列说法正确的是 ( )
A．平行板电容器两板的电势差不变
B．平行扳电容器带电量不变
C．平行板电容器两板的电势差增大
D．平行板电容器两板间的的电场强度不变
BCD
题目分析：本题S先触1后又扳到2，电容器所带电荷量不变
AC、由
可知，板间距离增大，C减小，Q不变则U增大；A错误,C正确
B、扳到2后，电容与电路断开，极板上的电荷就不会移到别处；正确
D、
，式中各量均不变，则电场强度不变，与板间距离无关；正确
故选BCD
点评：中等难度。影响电容的因素有很多，实验中采用控制变量法，即使一个物理量发生改变时，控制其他变量不变，这样容易发现规律．(这种方法在物理研究中经常用到)
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| Yesterday evening I was watching the evening news on TV. The news was about a prize for scientific discoveries. The 1 said something that caught my 2 . "All great discoveries," he said, "are made by people between the ages of 25 and 30." Being a little over 30 myself, I wanted to 3 with him. Nobody wants to think that he has passed the age of making any 4 . The next day I went to the public library, spending several hours, and 5 to find the ages of famous people and their discoveries. The announcer was right! First, I looked at some of the 6 discoveries. One of the earliest, the famous one that 7 that bodies of different weights 8 at the same speed, was made by Galileo when he was 26. Madam Curie started her research that led to a Nobel Prize when she was 28. Einstein was 26 when he 9 his world-changing Theory of Relativity. Well, 10 of that. Yet I wondered if those "best years" were true in other 11 . Then how about this in 12 ? Surely it needs the wisdom of 13 to make a good leader. Perhaps it does, but look when these people 14 their careers. Winston Churchill was elected to the House of Commons at the age of 26. Abraham Lincoln 15 the life of a country lawyer and was elected to the government at what age? Twenty-six! But why don't best years come after 30? After 30, I 16 , most people don't want to take risks or try new ways. Then I thought of people 17 Shakespeare and Picasso. The 18 was writing wonderful 19 at the late age of 50, 20 the latter was still trying new ways of painting when he was 90! Perhaps there is still hope for me. | ||||
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