电动力学的研究对象是电磁场的基本属性，电磁场的运动规律以及它和带电物质之间的相互作用.本文通过探究一个电动力学中的常见问题：已知极化强度求解束缚电荷的体密度，使学生在情境中产生疑难，在疑难中发现新问题，激发学生的认知冲突. 在教学过程中，重视知识和方法的应用及迁移，引起学生积极思维，培养学生科学思维和科学探究的能力.

 The research object of electrodynamics is the basic properties of the electromagnetic field, the law of motion of the electromagnetic field and the interaction between it and charged matter. This paper explores a common problem in electrodynamics: solving the bulk density of bound charges with known polarization strength, so that students will have difficulties in the situation, find new problems in the difficulties, and stimulate students^, cognitive conflicts. In the teaching process, emphasis is placed on the application and transfer of knowledge and methods, arousing students^, positive thinking, and cultivating students^, scientific thinking and scientific inquiry abilities.