问题 选择题

在竖直方向的匀强磁场中,水平放置一个面积不变的单匝金属圆线圈,规定线圈中感应电流的正方向如图甲所示,取线圈中磁场B的方向向上为正,当磁场中的磁感应强度B随时间t如图乙变化时,以下四图中正确表示线圈中感应电流变化的是

答案

答案:A

解答:解:在0-内,根据法拉第电磁感应定律,E===.根据楞次定律,感应电动势的方向与图示箭头方向相反,为负值;在-T内,根据法拉第电磁感应定律,

E′===.根据楞次定律,感应电动势的方向与图示方向相反,为负值.且电流为0-内的2倍,故A正确

故选A

点评:解决本题的关键掌握法拉第电磁感应定律E=n=n,会根据楞次定律判断感应电动势的方向.

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       Tom   1   a very good student, and he   2   doing homework, because he liked   3   other things in his
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