问题 选择题

三条在同一平面(纸面)内的长直绝缘导线组成一等边三角形,在导线中通过的电流均为I,方向如图所示。a、b和c三点分别位于三角形的三个顶角的平分线上,且到相应顶点的距离相等。将a、b和c处的磁感应强度大小分别记为B1、B2和B3,下列说法正确的是(    )

A.B1=B2<B3

B.B1=B2=B3

C.a和b处磁场方向垂直于纸面向外,c处磁场方向垂直于纸面向里

D.a处磁场方向垂直于纸面向外,b和c处磁场方向垂直于纸面向里

答案

AC

题目分析:由安培定则可知,a点附近两根导线在a处产生的磁场磁感应强度相互抵消,a点处的磁感应强度等于第三条通电导线在此处产生的磁感应强度,即垂直纸面向外,而b点与a点有相同的情况,有两根相互抵消,则由第三根产生磁场,即为垂直纸面向外,而在c点三根导线产生磁场方向相同,所以叠加而成的磁场垂直纸面向里且最强,故A、C正确,B、D错误。故选AC

完形填空

When Dan Shaw gets up from the sofa in his home, Cuddles is never far away. When he wants to go outside, he doesn’t take Cuddles out for a walk—Cuddles takes him for a walk. Cuddles is clearly no ordinary family pet. It is a two-foot-high miniature horse and serves as the guiding eyes of Shaw, who is blind.

When Shaw lost his sight, his wife suggested he apply for a guide dog. Shaw, an animal lover, said he couldn’t bear to part with a dog (which usually lives about eight to ten years) and get used to a new one, perhaps several times in his life.

Then Shaw heard of a program about the tiny guide horses. He learned that the horse possess many qualities that that make them an excellent choice for guiding people. They are clean, friendly, smart and have great memories. They can be trained to remain calm in noisy and crowded places. Best of all, they live for 25-25years, which would enable Shaw to have the same guide companion for most or all of his life.

Shaw immediately applied to be and was accepted as the first person to receive a guide horse. The instant he met Cuddles, he knew he was making the right choice. Then he began his training.

Through training, Shaw and Cuddles learned to find way on busy streets, step over curbs(便道沿儿)and find elevator buttons. Cuddles even demonstrated(显示)its ability to step in front of Shaw and block him, to prevent him from walking into a dangerous situation. The little horse also expertly led Shaw through busy shopping malls. They got along without any difficulty. Now Shaw is confident that Cuddles will change his life for the better.

小题1:What’s the meaning of the underlined word “miniature” in Paragraph 1? (No more than 2 words)

小题2:Why didn’t Shaw want to choose a dog as his guide? (No more than 15 words)

小题3:What does Paragraph 3 mainly tell us? (No more than 10 words)

小题4:How does Shaw feel about his future life with the help of Cuddles? (No more than 10 words)

小题5:In your opinion, what is the ideal relationship between man and animals? (No more than 20 words)

问答题 简答题