A criterion of zero magnetic field point, which is related with the symmetry of current-carrying system, is derived from a simple problem.

从一个简单问题出发，引出关于磁场零值点的一个判据，该判据与载流系统的几何对称性有关。

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With the structure symmetry, the expressions of the electric-field on the point of a half conductor cylinder are given, and the electric-field characteristics are analyzed.

利用其结构的空间对称性，计算出该理想模型半球壳顶端附近的电场表达式，并对电场特性作简单分析。

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The conservation principle of orbital symmetry may be represented as conservation law of bond symmetry, by means of group theory and the point of view of the localized bonds.

利用群论的方法及定域键的观点可以把轨道对称守恒原理表述为键对称守恒规律。

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