问题 问答题

如图所示是探究电磁感应现象的装置.

(1)闭合开关.让导体AB沿水平方向左右运动.观察到灵敏电流计的指针偏转;若让导体AB由图示位置沿竖直方向上下运动.则灵敏电流计的指针______ (选填“偏转”或”不偏转”).

(2)利用此装置.探究感应电流方向与磁场方向和切割磁感线方向之间的关系,观察到的实验现象记录如下:

实验序号磁场方向导体切割磁感线方向灵敏电流计指针偏转方向
向下向右向左
向上向右向右
向下向左向右
向上向左向左
在上述四次实验中.比较______两次实验,可知感应电流方向与磁场方向有关;比较______两次实验,可知同时改变磁场方向和切割磁感线方向则感应电流方向不变.

(3)在探究中还发观.导体AB水平同左(或向右)缓慢运动时.灵敏电流汁的指针偏转角度较小;导体AB水平向左(或向右)快速运动时,灵敏电流计的指针偏转角度较大.说明感应电流的大小与______有关.

(4)有同学还想探究感应电流的大小是否与磁场强  弱有关.请写出简要做法:______;如何判断:______.

(5)如图所示是实验室用到的手摇发电机模型,将小电灯换成灵敏电流汁.慢慢摇动手柄,观察到灵敏电流计的指针______(选填“左右摆动”或“向一侧摆动”).这表明该发电机模型发出的电是______(选填“交流电”或“直流电”).

答案

(1)导体沿竖直方向运动,运动方向与磁场平行,故不切割磁感线,不会产生感应电流,指针不发生偏转.

(2)比较实验1和2(或3和4)可知:在导体切割磁感线运动方向一定时,改变磁场方向,感应电流的方向发生改变;比较实验1和4(或2和3)可知:在导体切割磁感线运动方向(或导体运动方向)不变时,磁场方向改变,感应电流的方向就改变.

(3)导体AB水平同左(或向右)缓慢运动时.灵敏电流汁的指针偏转角度较小;导体AB水平向左(或向右)快速运动时,灵敏电流计的指针偏转角度较大,这说明电路中的电流变大,所以可以看出感应电流的大小与导体的运动快慢有关.

(4)因为导体是否运动、磁场的有无都影响了感应电流的大小;所以设计实验步骤时采用控制变量法;即:保持切割磁感线运动的速度不变,改变磁场的强弱,利用电流表指针的偏转幅度表示感应电流的大小.

(5)发电机中的线圈在磁场中转动,在转动一周的过程中,线圈中的一段导体先从最上端到最下端后又从最下端到最上端.利用右手定则可知,感应电流的方向与导体运动方向和磁场方向有关,在磁场方向不变的情况下,导体运动方向改变,感应电流的方向也随之改变,所以,灵敏电流计的指针是左右摆动,并说明发电机发出的电流的大小是不断变化的,发出的是交流电;

答:(1)不偏转;(2)1和2(或3和4);1和4(或2和3);(3)导体的运动快慢;

(4)保持切割磁感线运动的速度不变,改变磁场的强弱;电流表指针的偏转幅度;(5)左右摆动;交流电.

阅读理解

B

  More and more young people enjoy having pets,but they don't like to keep them.At present in Changchun,people prefer to rent pets and play with them during weekends,regarding this as a fashionablelifestyle.

  Mr.Feng,from Jilin Province,likes pet dogs.Last weekend he rented a Scottish shepherd dog from a localpet shop.He bathed the dog,and went walking with it.He said he could not keep pets in his spare time because he was busy everday except weekends.To rent pets during weekends seemsto be the most practical and economical way to relax himself.

  A manager from a pet shop says his customers(主顾) are all like Mr.Feng,usually too busy to keeppets,and some of them have never kept any pets before. But they hope torent pets and learn to keep pets so that they can know whether they can be good pet masters or not.

  It's reported that all pets for rent need to beimmunized(免疫).Before they are rented out,pet shops will teach their customers the ABCs of pet keeping and preparing pet food based on each pet's taste.

  Shop assistants will also provide(提供)different konds of services for pets like health checkup if their customers want to rent pets for a longer period.

  Dogs for rent are often not ordinary ones,so their rent is high,usually 200 - 500 yuan(US$ 25-63) per day.Sometimes,you have to leave thousands of yuan with the owner before you can take a dog away.

  60.Mr.Feng rents pets instead of keeping them mainly because _______.

  A.it's cheaper                  B.it is more fun

  C.he has little spare time         D.he wants a new pet for each week

  61.What do we know about those who rent pets?

  A.None of them ever kept a pet before.

  B.They'll become pet owners later.

  C.They enjoy having pets.

  D.They want to help protect animals.

  62.The underlined phrase "the ABCs(of…)"in the 4th paragraph refers to "______(of…)".

  A.the possible dangers           B.the basic knowledge

  C.the communicative language    D.the rules set by the shops

  63.The dogs' rent is high because___________.

  A.the customers are rich           B.there are few dogs to rent

  C.their owners hate to leave them    D.they are top - class dogs

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