问题 填空题

面积为0.1m2的120匝矩形线圈放置在与线圈平面垂直的匀强磁场中,线圈总电阻为1.2Ω,磁感应强度随时间变化如图所示,则0.3s内穿过线圈的磁通量的变化量为______Wb,0.2-0.3s内电流所做的功为______J.

答案

0.3s时穿过线圈的磁通量∅=BS=0.2×0.1 Wb=0.02Wb,

则0.3s内穿过线圈的磁通量的变化量为△∅=∅-0=0.02Wb

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
=
0.2-0.1
0.3-0.2
T/s=1T/s
,根据法拉第电磁感应定律得

    E=n

△∅
△t
=n
△B
△t
s=120×1×0.1V=12V

则0.2-0.3s内电流所做的功为W=

E2
R
 t=
122
1.2
×0.1J=12J

故答案为:0.02;12.

阅读理解

Lately, Bolivia has outlawed (宣布……为非法) the use of animals in circus (马戏团) performances, and officials in the South American nation aren’t doing it in a silly way! They say all Bolivian circuses must stop using animals.

Some people welcome the law. They say animals should not be forced to work and that circus creatures are caged in tight spaces when they travel. However, other people say that many of the four legged performers are cared for by animal experts. Plus, they point out, circus animals entertain millions of fans.

Should animals perform in circuses? Student reporters Michael and Emily have done some work on the issue.

Yes, I think animals should be allowed in circus acts. Most circus trainers love and respect the animals they work with and treat them well. Certain rules and regulations also help to ensure that the animals are treated humanely, or with kindness. Millions of people love circus animals. They look forward to seeing elephants and tigers perform. Many of the animals are exotic (奇特的), so people might not get the chance to see them anywhere else. “Circus animals shouldn’t be banned,” says Parker, a sixth grader from Oregon City, “One of the main reasons people go to the circus is to see animals they don’t see every day and to see them do cool tricks.”

Animals should not perform in circuses. When animals are in circuses, they are forced to learn new behaviors in order to entertain humans. Those behaviors may go against their natural instincts (本性). For example, bears  hibernate  in the winter, but bears in a circus have to perform and can’t hibernate as their bodies tell them to. Also, circus animals have to travel all the time in cages. All that traveling may cause them to become confused or upset because their environment keeps changing. “When animals are removed from their habitat and held in cages ... it changes their behaviors,” points out Anne Northam, a teacher from Friendswood, Texas.  “They are no longer selfsufficient (自给自足的).”

小题1:Which of the following can be a reason why people support the law?

A.Animals in circuses are given more respect and care.

B.Animals in circuses bring a lot of fun for people.

C.Animals in circuses can’t live their life naturally.

D.Animals in circuses are protected by many regulations.小题2:What’s Anne’s attitude towards the new law?

A.She welcomes it.

B.She is against it.

C.She thinks it acceptable.

D.She thinks it useless.小题3:Which would be the best title for the text?

A.Enjoy more fun in circuses

B.More respect and kindness to animals

C.Circuses in Bolivia Open or Closed

D.Animals belong in circuses Yes or No小题4:The underlined word “hibernate” in the last paragraph probably means __________.

A.sleep

B.look for food

C.move from one place to another

D.perform

填空题