问题 选择题

用显微镜观察玻片时,下列哪一个叙述是错误的?(  )

A.先使用低倍物镜找到要观察的物体

B.由低倍镜换成高倍镜时,视野内的物像变大

C.由低倍镜换成高倍镜时,视野内的亮度变暗

D.若其他条件不变,则物镜越长,放大倍数越低

答案

显微镜呈放大的像,放大倍数=目镜倍数×物镜倍数,显微镜的放大倍数越大,视野越暗,所看到的物像越大;放大倍数越低,视野越亮,所看到的物像越小.物镜倍数越高,镜头越长;目镜倍数越高,镜头越短.

A、低倍镜,放大倍数小,看到的物像范围大,容易找到物像,因此先使用低倍物镜找到要观察的物体.故该选项不符合题意;

B、由低倍镜换成高倍镜时,显微镜的放大倍数变大,看到的物像越大.故该选项不符合题意;

C、由低倍镜换成高倍镜时,高倍镜的透光率较小,显微镜的放大倍数变大,视野内的亮度变暗.故该选项不符合题意;

D、物镜越长,物镜倍数越高,显微镜的放大倍数变大.故该选项不符合题意.

故选:D.

阅读理解

Read and choose.(阅读短文,回答问题)  

     Mr Jones and Mr Brown worked in the same office. One day Mr Jones said to Mr Brown,

"I am going to have a small party at my home next Wednesday evening. Would you and your

wife like to join us?"

     Mr Brown said, "Thank you very much. It is very kind of you. We will be free that evening,

I think. But I will t.elephone my wife and ask her. Maybe she wants to go somewhere else that

evening." So Mr Brown went to the other room and telephoned.

     When he came back, he looked very sorry.

     "What is the matter?" said Mr Jones. "Did you speak to your wife?"

     "No," answered Mr Brown, "She wasn't there. My small son answered the telephone. I said

to him, 'Is your mother there, David?' And he answered, 'No, she is not in the house,' 'Where

is she  then?' I asked. ' She is somewhere outside.' 'What is she doing?'  'She is looking for me.'"

1. A small party will be held _____.      

A. at David's house                      

B. at Mr Brown's house

C. in the office                          

D. at Mr Jones' house

2. The small party will be held _____.       

A. next Wednesday even.ing                

B. next Monday evening

C. next Friday evening                    

D. next Wednesday morning

3. Mr Jones asked _____ to the party.       

A. Mr Brown                            

B. Mrs Brown

C. Mr and Mrs Brown                    

D. all his friends

4. The telephone was _____.                

A. in the same office                      

B. in a room next to the office

C. in the post office                      

D. near Mr Jones' house

5. Mr Brown spoke to _____ on the phone.       

A. Mrs Brown                          

B. Mrs Jones

C. David                                

D. David's friend

单项选择题