问题 问答题

有一横截面积为0.2m2 的100 匝圆形闭合线圈,线圈总电阻为0.2Q,线圈处在匀强磁场中,磁场垂直线圈平面向里增强,其磁感应强度 B 随时间 t 的变化规律如图所示.则线圈中感应电流的方向和感应电流的大小如何?

答案

由图看出,磁感应强度增大,则穿过线圈的磁通量增大,根据楞次定律判断则知,线圈中感应电流方向为逆时针;

由图象的斜率求出

△B
△t
=0.02T/s,根据法拉第电磁感应定律得

    E=n

△Φ
△t
=n
△B
△t
s=100×0.02×0.2V=0.4V

则感应电流的大小为  I=

E
R
=2A

答:线圈中感应电流的方向为逆时针,感应电流的大小为2A.

阅读理解

Dear Florence,

We arrived in India last week, and the voyage was the worst experience of my entire life. I’m lucky to be alive!

The first part of the journey was terrible, because the ship hit bad weather almost as soon as we left Liverpool. But much, much worse was to come. Later, we were involved in a collision with another boat and we had to abandon ship!

We had been at sea for about two weeks and we were in the Mediterranean. There is now a canal between the Mediterranean and the Red Sea called the Suez Canal, which opened last year. Our boat stopped at Port Said, the Egyptian port at the entrance to the canal. I remember looking through the porthole of my cabin and wishing that I could go ashore and visit this fascinating place, but mummy had ordered that I was to stay in the cabin because I was feeling ill. “you must stay here for at least another two days.” I remember her saying. How wrong she would turn out to be! The ship left the port and headed towards the canal . I was alone in the cabin and I watched the port disappear into the distance. Suddenly there was a loud bang, followed by the most awful crunching(嘎吱的)sound, and the ship shook and turned slightly on its side.

There was an eerie silence for a moment, then people started shouting. Mummy came running into the cabin and told me that we had collided with another boat. She took my hand and we ran along the deck towards the lifeboats. There was a lot of shouting and people were running everywhere, but the crew were all acting calmly, helping people into the lifeboats and telling people not to panic.

Well, clearly we survived, as did all the passengers and crew of the ship. The other boat wasn’t so lucky. It sank and several lives were lost.

I will write about the rest of the journey soon. Please give my love to Aunt Claire and Uncle Eric.

Your loving cousin,

Jane

56.小题1:When was the letter written?

A.Before the author went to India.

B.In the mid – 19th century.

C.When the author arrived in Egypt.

D.Just after the author arrived in India.57.小题2:Why was the journey to India such a bad experience for the author?

A.She was sick when it started and nearly died in Egypt.

B.Her ship left England in bad weather and crashed into another ship near the Suez Canal.

C.She was seasick when her ship sank.

D.She was alone when her ship hit another boat and she got sick.58.小题3:The author’s mother didn’t allow her to go ashore and visit the port city, Said because      .

A.she was homesick at that time

B.she didn’t feel very well then

C.she could meet some danger ashore

D.she could see the city through the porthole on board59.小题4:The underlined phrase “eerie silence” in the sixth paragraph means         .

A.pleasant calm silence

B.long peaceful silence

C.sudden long silence

D.strange uncomfortable silence

单项选择题