试题与答案

老师做了一个物理小实验让学生观察:如图所示,一轻质横杆两侧各固定一金属环,横杆可

题型:选择题

题目:

老师做了一个物理小实验让学生观察:如图所示,一轻质横杆两侧各固定一金属环,横杆可绕中心点自由转动,老师拿一条形磁铁插向其中一个小环,后又取出插向另一个小环,同学们看到的现象是(   )

A.磁铁插向左环,横杆发生转动

B.磁铁插向右环,横杆发生转动

C.无论磁铁插向左环还是右环,横杆都不发生转动

D.无论磁铁插向左环还是右环,横杆都发生转动

答案:

答案:B

题目分析:左环不闭合,磁铁插向左环时,不产生感应电流,环不受力,横杆不转动;右环闭合,磁铁插向右环时,环内产生感应电流,环受到磁场的作用,横杆转动;

故选B.

点评:穿过闭合回路的磁通量发生变化,闭合回路中会产生感应电流,感应电流受到磁场力的作用,横杆转动;如果金属环不闭合,穿过它的磁通量发生变化时,只产生感应电动势,而不产生感应电流,环不受力的作用,杆不转动.

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The bicycle was    8      the next day, and Gayle's dream came true. The following day I received a letter that read:

Dear Bonnie,

Once in a while there is an opportunity to pass on a    9        I lost my parents to cancer six months ago. I cared for both of them but could not have done it without the love and generosity of friends - friends who   10       .

The best to you,

Norma

It was from the owner of the ice cream stand. Enclosed was my uncashed check.

(  ) 1. A. expressed                     B. whispered                 C. told                  D. ordered

(  ) 2. A. realize                         B. appear                      C. happen             D. come true

(  ) 3. A. daily                           B. weekly                     C. monthly            D. yearly

(  ) 4. A. in the charge                B. in charge                  C. in office            D. in public

(  ) 5. A. to say                          B. to tell                       C. to weep             D. to speak

(  ) 6. A. tighten                        B. loosen                      C. dry                   D. wet

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(  ) 10. A. care                           B. treasure                    C. value                D. promise

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