如图所示为一磁流体发电机示意图,A、B是平行正对的金属板,等离子体(电离的气体,

题型:选择题

问题:

如图所示为一磁流体发电机示意图,A、B是平行正对的金属板,等离子体(电离的气体,由自由电子和阳离子构成,整体呈电中性)从左侧进入,在t时间内有n个自由电子落在B板上,则关于R中的电流大小及方向判断正确的是(  )

A.I= ,从上向下

B.I= ,从上向下

C.I= ,从下向上

D.I= ,从下向上

考点:电流路端电压
题型:选择题

阅读理解。

     Two men were sitting together in a plane.  They were on a long journey (旅行).One of them was a

teacher. The other was a farmer. They sat without talking for a while, then the farmer said, Let's do

something to pass the time."

     "What do you want to do?" the teacher asked.

     "We can ask each other riddles," said.the farmer.

     "Let's make the rules first," the teacher said. "And let's make the game moreinteresting.  Let's play it

for money.  If we don't know the answer to a riddle,  we have to pay $ 50. "

     The farmer thought about this for a while, then he said. "That's not fair. You are a teacher,  an

educated man. You know more things than I do. I am just a farmer." "That's true, " the teacher said, 

"What do you think we should do?" "If you do not know the answer to a riddle,  you pay me $ 100. If I

do not know the answer to a riddLe,  I will pay you $ 50. " the farmer said.

     The teacher thought about this, then he said, "OK, that's fair. Who will go first?" "I will," the farmer

said, "Here's my riddle. What has three legs when it walks, but only two legs when it flies?"

     The teacher repeated the riddle, "What has three legs when it walks, but only two legs when it flies?

Mm, that's a good one. I'm afraid I don't know the answer." He gave the farmer $ 100, then said,

"Tell me the answer. What has three legs when it walks, but only two legs when it flies?" "I don't know."

the farmer said,  and gave the  teacher $ 50.

1. Two men were sitting in an airplane     __     .

A. on their journey home          

B. on their way to a farm

C. on a long journey              

D. on their way to school

2. They decided to pass the time by   ____   .

A. reading the newspaper        

B. asking each other riddles

C. playing cards                

D. talking about their families

3. If the farmer didn't know the answer to a riddle, he had to pay the teacher     ___  .

A. $50      

B. $100      

C. $200      

D. $l

4. A teacher is    ___   than a farmer.

A. well-educated            

B. poor-educated

C. better-educated              

D. worse-educated

5. In the end, the teacher paid the farmer     __     .

A. $50      

B. $150    

C. nothing    

D. $200

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