问题 实验题

用伏安法测电池的电动势和内电阻,由于电路存在问题,当电键S闭合后,移动变阻器的滑片P时,出现下列异常现象:

(1)电流表示数可变,电压表示数始终为零

(2)电流表示数为零,电压表示数不变

(3)电流表烧坏

(4)电流表示数不变,电压表示数可变

以上四种情况与下面电路图对应的情况分别是:(1)对应     ,(2)对应     

(3)对应      ,(4)对应       .

答案

(1)丁;(2)乙;(3)甲;(4)丙。

试题解析:在甲电路中,由于电流表与电源直接连接,故闭合开关时,电流表将被烧坏,故它对应的是(3);乙电路中电压表串联在了电路中,而其电阻较大,故当移动变阻器的滑片P时,电压表的示数一直约等于电源电压,而电路中的电流约为零,故它对应于(2);丙电路中变阻器的最大电阻接在了电路中,故电路中的电流始终不变,电压表的示数是可变的,故它对应于(4);丁电路中电压表并联在了电流表的两端,故电压表的示数始终为零,电流表的示数是可变的;故它对应于(1)。

单项选择题
阅读理解

TS said that everyone has a changing circle of friends. However, no matter how frequently we renew our phone books, some names always remain. These names remind us of the good times we spent together with our friends. Though we may not see them every  day, they will always stay in our hearts.

Tom was often called "Big Head" at school because of his extraordinarily large head. He was one of my close friends at primary school. But since graduation, we have been studying in different cities and haven't seen each other for a long time.

Several days ago, I received an e-mail saying that my former classmates from primary school were holding a party to get together and chat about past memories. I was so excited because [ would get to see Tom again. What would he look like now? Would we still feel as close to each other as we had done back then? I was a little frightened about what I would find.

When I arrived at the party, I did manage to recognize Tom. However, he was much taller than he had been before. What's more, his head was no longer big.

"Hi, Buddy. Do you recognize me?" Tom walked towards me.

"Of course. How could I ever forget our ' Big Head' ," I said jokingly, "But where has your big head gone?"

"Haha, maybe it didn't keep up with the steps of time and stayed in the past," Tom patted his own head and answered with a laugh.

All my misgivings suddenly disappeared. I realized that time had changed us outwardly, but our friendship hadn't changed at all. I chatted happily with Tom about our shared experiences in primary school.

Then I looked around the small room and saw different faces, both familiar and unfamiliar, but none of them the faces of strangers. The whole party was filled with a warm atmosphere. Everyone was lost in the sweet memories of childhood. They forgot all their present-day stresses and pressures.

"Hey, what are you thinking about? Come and get some pizza!" A call from a friend woke me up from my thoughts. I hurried towards the table. "Wait! That biggest piece is mine!"

小题1:Why are some names always in our phone books?

A.Because everyone has a changing circle of friends.

B.Because we sometimes forget to renew phone books.

C.Because we'll never forget some of our friends.

D.Because our circle of friends will not change.小题2:According to the passage, which of the following statements is TRUE?

A.Tom has changed a lot since primary school.

B.Tom invited the author to the get-together party by email.

C.The author recognized Tom immediately because of his big head.

D.Tom couldn't recognize the author at the first sight.小题3:What does the underlined word "misgiving" mean (in para. 8 )?

A.expectation and excitement

B.worries and doubts

C.stresses and pressures

D.shyness and nervousness小题4:The author writes the last paragraph to show

A.others can't understand what the author is thinking about

B.The pizzas are not adequate for everyone in the party

C.the author wants to have a big pizza very much

D.the author enjoys the warm atmosphere of the party greatly小题5:Which of the following proverbs can be used to conclude this passage.'?

A.A friend in need is a friend indeed.

B.Time reveals a person's heart.

C.Friends are like wine; the older, the better.

D.A faithful friend is hard to find.