问题 选择题

一正方形闭合导线框abcd,边长为L=0.1m,各边的电阻均为0.1Ω,bc边位于x轴上且b点与坐标原点O重合。在x轴原点O的右侧有宽度0.2m、方向垂直纸面向里的匀强磁场区域,磁场的磁感强度为0.1T,如图2甲所示。当线框以4.0m/s的速度沿x轴匀速运动穿过磁场区域时,图乙中的图象表示的是线框从进入磁场到穿出磁场的过程中,线框的感应电流随位置变化的情况,其中正确的是

答案

答案:A

线框进入磁场还有出磁场时都会产生感应电流,根据楞次定律可知,感应电流的方向是阻碍磁通量的变化,故进入磁场时产生逆时针方向的电流,出磁场时会产生顺时针方向的感应电流,即可排除BC,因为线框做匀速运动,所以产生稳定的电动势(E=BLV)所以电流大小恒定,只是方向发生改变

故选:A

填空题

根据短文内容及首字母提示完成短文。

     Usually, doctors tell some people to go on  diets( 节食).  The doctors hope the diets will make the

people feel b    l    . They hope the diets will make the people healthy.

     Alana was on a diet, but she didn't like it at all. She wasn't a    2    to eat her favorite food by the

doctor. While her brother Frank ate chocolate, she had to eat an apple. Alana was on the diet for two

months. Her doctor was pleased with her. "You have been very good," he said.“You can eat some of

the food you like best but only a little. Don't eat too many sweets. Don't eat too much ice-cream.  If you

do, you will get a lot of weight a    3    . "

     Then the doctor put Frank on a diet. It was a different kind of diet. “You c    4    eat chicken or eggs,

Frank," said the doctor. "They will make you in trouble. "

     "How long will I have to be on the diet?" asked Frank.

     "A long time,” said the doctor.  “Maybe for the r    5    of your life. "

     "But I really  like  chicken,"  said  Frank.

     " You said it is one of the best meat to eat. "

     "It is very good food for most people," said the doctor.  "But when you eat it, it will make you sick. It

is not good food for you. "

          "You're right,"  said Frank.  "Well, I’ll eat more cake instead."

    1.            2.             3.             4.             5.             

单项选择题 B1型题