高中《物理》（必修）第二册第１６面静电除尘器示意图如图１所示，高中《物理》（选修）第三册第２０６面插图如图２所示，由这两幅图我们可以看到，除尘器的金属管Ａ、平行板电容器的一个极板和静电计，它们都接了地，为什么呢？这个问题，老师常常忽略，学生也不清楚．图１ The schematic diagram of the electrostatic precipitator of the 16th surface of High School “Physics” (required) Book 2 is shown in Figure 1. The 206th illustration of the third volume of the “Physics” (optional) in high school is shown in Figure 2. From these two figures we can See that the metal pipe A of the dust collector, a plate of the parallel plate capacitor, and the electrometer are all connected to the ground. Why? This question is often overlooked by the teacher and it is not clear to the students. Figure 1