问题 选择题

对于理想变压器来说,下列说法中不正确的是(   )

A.变压器是利用互感现象制成的

B.变压器可以改变各种电源的额定功率

C.变压器不仅能改变电压,还同时改变电流

D.变压器的初级电流随次级电流的增大而增大

答案

答案:B

题目分析:变压器的原线圈中的电流变化,在副线圈中感应出电流,这种现象叫互感,故A正确;输入功率等于输出功率,故B错误;变压器的匝数与电压成正比,与电流成反比,故C正确;因为电流与匝数成反比,所以原副线圈电流同时变化,故D正确;

让选错误的,故选B

点评:变压器的原理是电磁感应,输入功率等于输出功率,电压与匝数成正比,电流与匝数成反比.

阅读理解

阅读下文,判断下列句子是否符合短文内容,符合的用“A”,不符合的用“B”。    

     A man named Nick went on a fishing holiday. Fishing was his favorite sport, and he had many prizes for

  fish he had caught.

    One summer, the weather was nice and the fishing was supposed to be good, so he decided to travel

 around the country, spending a few days fishing in the river.

    Unfortunately, he wasn't so lucky that he caught only a few small fish.  Later, he heard of a large river

 that was full of fish nearby.

    He found the river quite easily and it flowed through a farm. He decided to ask the farmer's permission

 (许可)to fish in the river.

    "You have my permission," the farmer said, "but you should be careful. For years I stopped my kids

 from going near that river."

    "Is the river dangerous?" Nick asked.

   "It's not the river," the farmer said, "It's the fish. They're so big that my kids couldn't hold them."

    Nick was very excited. All fishermen wanted to catch really big fish.

    "How big are they?" he asked.

    "Well," the farmer told him.  "Last week I lost one over three feet long, and yesterday I lost one just

 over four feet long.”

     "What bad luck!" Nick said. "I hate losing a big fish once I've hooked him."

    "Who's talking about fish?" the farmer said angrily. "It's two of my kids that I lost!"

( ) 1. Nick's favorite sport is fishing.

( ) 2. When Nick was traveling around the country, the weather was rainy.

( ) 3. The farmer didn't let Nick fish in the river.

( ) 4. There are real big fishes in the river that is through the farm.

(     ) 5. The farm's two sons had lost their lives.

填空题 案例分析题