为什么把大地规定为零电位？

电位是描述电荷在空间中分布的物理量。在讨论电位时，我们常常将大地定义为零电位。那么，为什么选择大地作为电位的参考点呢？这个问题涉及到电势的定义和基准点的选择。

首先，电势是一个相对值。在物理学中，电势被定义为单位正电荷所具有的势能。而势能是一个相对概念，它与参考点的选择有关。在电位的计算中，我们需要选择一个作为基准的点，其他点的电势值就是相对于这个基准点的。

在选择基准点时，我们希望选取一个易于获得且稳定可靠的参考点。而大地恰好符合这个条件。大地是我们所处的地球表面，它与我们相互接触，并且质量庞大、稳定可靠。因此，将大地作为电位的基准点是一种方便而实用的选择。

此外，将大地定义为零电位也有利于测量和比较电势。当我们使用电位差计（电压表）进行测量时，它的一个引线通常会与大地相连，以确保测量的精度和准确性。这种设置使得我们可以方便地将电位与大地的电位进行比较。在电力系统、电子设备和通信系统中，很多电路都是相对于大地进行设计和连接的，因此选择大地作为零电位也有助于简化电路分析和设计。

总之，将大地规定为零电位是出于实用和方便的考虑。作为一个易于获得且稳定可靠的参考点，大地为电势提供了一个基准值，便于测量和比较电位。这种规定为电路设计和分析提供了便利，并促进了电力系统、电子设备和通信系统的发展。

Why is the Earth defined as zero potential?

Potential is a physical quantity that describes the distribution of charges in space. When discussing potential, we often define the Earth as zero potential. So, why choose the Earth as the reference point for potential? This question involves the definition of potential and the choice of reference point.

Firstly, potential is a relative value. In physics, potential is defined as the potential energy per unit positive charge. Potential energy is a relative concept, and it is related to the choice of reference point. In calculating potential, we need to choose a point as the reference, and the potential values of other points are relative to this reference point.

When choosing a reference point, we want to select a point that is easy to obtain and stable. The Earth fits these criteria perfectly. The Earth is the surface we live on, it is in contact with us, and it has a massive and stable mass. Therefore, choosing the Earth as the reference point for potential is a convenient and practical choice.

Furthermore, defining the Earth as zero potential is also beneficial for measuring and comparing potentials. When using a voltmeter for measurement, one of its leads is usually connected to the Earth to ensure accuracy and precision. This setup allows us to conveniently compare the potential with the potential of the Earth. In power systems, electronic devices, and communication systems, many circuits are designed and connected with respect to the Earth. Therefore, choosing the Earth as zero potential also simplifies circuit analysis and design.

In conclusion, defining the Earth as zero potential is based on practical and convenience considerations. As an easily obtainable and stable reference point, the Earth provides a benchmark for potentials, facilitating their measurement and comparison. This convention also benefits circuit design and analysis, promoting the development of power systems, electronic devices, and communication systems.