两个同心带电球壳体系电磁场角动量的研究

摘要

Electromagnetic momentum and angular momentum are interesting and basic topics of classical electromagnetism.According to the basic electromagnetic theory,the angular momentumLem =ε0∫vr × (E×B)dV.For static case,it can also be expressed asLem =∫r×ρAdV,which is analyzed simply in this paper.Through a simple electromagnetic system,which contains two concentric insulated charged spherical shells with the bigger one is rotating,change of the angular momentum of the total system is discussed.We conclude that in the process of establishing a static electromagnetic field,part of the impulse moment provided by the external force is converted into the electromagnetic angular momentum which is stored in the field,and part of it is converted into the rotatingmechanical momentum of the system.When the field is removed,the electromagnetic angular momentum converts into the mechanical angular momentum,and the total angular momentum of the system is conserved.%电磁场的动量和角动量是经典电磁学有趣而又基本的问题.根据标准电磁理论,电磁场角动量可表示为Lem=ε0∫vr×(E×B)dV,对恒定电磁场,角动量还可以用Lem=∫r×ρA dV来计算,文章对此进行了分析.通过一个简单的模型,即一个固定的绝缘带电球壳处在另一个旋转的绝缘带电球壳中心,分析了该体系电磁场从建立到稳定,再到撤去的过程中,整个系统角动量的变化情况.验证了在建立稳定电磁场的过程中,外力提供的冲量矩一部分转化为电磁场角动量储存在电磁场中,一部分提供体系的转动机械角动量,当撤掉磁场后,电磁场角动量转换成机械角动量,整个过程角动量守恒.