题干

在倾角为θ的光滑斜面上,放置一段通有电流强度I,长度L,质量m的导体棒a(电流方向向里),如图所示.

①若空间中有竖直向上的匀强磁场,则磁场强度B1是多大?

②若磁场方向任意,要使导体棒a静止在斜面上且对斜面无压力,匀强磁场磁感应强度B2的大小和方向如何?

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答案(点此获取答案解析)

解:①若磁场方向竖直向上,由导线受力情况可知由平衡条件得:

在水平方向上:F﹣

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语法填空

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    Papercutting appeared in West Asia in the 16th century. The knowledge of paper making did not reach Europe until the 13th century. In Switzerland and Germany, for example, it was not until the 16th century____ papercut art was established.

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