Electric Fields | 电场

📚 Electric Fields | 电场

An electric field is a region around a charged object where another charged object experiences an electric force. This force can be attractive or repulsive and acts without direct contact. Understanding electric fields helps explain many phenomena, from static shocks to lightning and how photocopiers work. In GCSE Physics, you will learn how to draw field lines, describe the behaviour of charges, and link electric fields to potential difference.

电场是带电物体周围的一个区域，在这个区域中的其他带电物体会受到电场力的作用。这种力可以是吸引力或排斥力，并且不需要直接接触就能产生。理解电场有助于解释许多现象，从静电火花到闪电，再到复印机的工作原理。在 GCSE 物理中，你将学习如何绘制电场线、描述电荷的行为，并将电场与电势差联系起来。

1. What is an Electric Field? | 什么是电场？

An electric field exists in the space around any electrically charged object. If a second charged particle is placed within this field, it will experience an electrostatic force. The direction of the field is defined as the direction of the force on a small positive test charge placed at that point.

任何带电物体的周围空间中都存在电场。如果将另一个带电粒子放入这个电场中，它就会受到静电力的作用。电场的方向定义为放入该点的一个小的正检验电荷所受力的方向。

Electric fields are vector fields – they have both magnitude and direction. The stronger the field, the greater the force on a given charge. Fields are invisible, but we can represent them using field lines (also called lines of force).

电场是矢量场，既有大小也有方向。场越强，对给定电荷的作用力就越大。电场是看不见的，但我们可以用场线（也叫电力线）来表示它。

2. Electric Field Lines | 电场线

Electric field lines show the direction and strength of an electric field. The lines always point away from positive charges and towards negative charges. The closer the lines are together, the stronger the electric field in that region.

电场线表示了电场的方向和强度。这些线总是从正电荷出发，指向负电荷。线越密集的地方，该区域的电场就越强。

Key rules for drawing field lines: they never cross each other, they are perpendicular to the surface of a charged conductor, and they start on positive charges and end on negative charges. For a single isolated positive point charge, lines radiate outwards symmetrically. For a negative point charge, lines point radially inwards.

绘制场线的关键规则：它们绝不相交，垂直于带电导体的表面，并且从正电荷出发终止于负电荷。对于单独的正点电荷，场线呈球形对称向外辐射。对于负点电荷，场线则径向指向内。

3. Static Electricity and Charging | 静电与起电

Static electricity is the build-up of electric charge on the surface of an insulator. Charging occurs when certain materials are rubbed together, transferring electrons from one material to the other. The material that gains electrons becomes negatively charged; the one that loses electrons becomes positively charged.

静电是绝缘体表面电荷的积累。当某些材料相互摩擦时，电子会从一种材料转移到另一种材料，从而产生电荷。获得电子的材料带负电，失去电子的材料带正电。

This transfer happens because some materials hold onto their electrons more tightly than others. For example, rubbing a polythene rod with a cloth transfers electrons to the rod, making it negative, while the cloth becomes positive. This is called charging by friction.

这种转移的发生是因为有些物质相比其他物质对电子的束缚能力更强。例如，用布摩擦聚乙烯棒，电子会转移到棒上，使其带负电，而布则带正电。这称为摩擦起电。

4. Attraction and Repulsion | 吸引与排斥

Like charges repel each other, and unlike charges attract. This fundamental rule governs the behaviour of charged objects in an electric field. The force between two point charges can be felt even when they are not touching, which is evidence of the electric field.

同种电荷相互排斥，异种电荷相互吸引。这条基本规则支配着带电物体在电场中的行为。即使两个点电荷没有接触，它们之间也能感受到力的作用，这就是电场存在的证据。

The strength of the force depends on the amount of charge on each object and the distance between them. A greater charge produces a stronger force; increasing the separation reduces the force. This relationship is explored further with Coulomb’s law, but at GCSE you simply need to describe the trend.

力的大小取决于每个物体所带电荷量的多少以及它们之间的距离。电荷量越大，产生的力越大；增大距离会减小力。这种关系库仑定律会进一步探讨，但在 GCSE 阶段你只需要描述这个趋势。

5. Conductors and Insulators | 导体与绝缘体

Conductors, such as metals, allow electric charge to flow through them easily because they contain free electrons that can move. In an electric field, these free electrons rapidly redistribute themselves, cancelling the field inside the conductor. This is why the interior of a metal object has zero electric field in electrostatic equilibrium.

导体（如金属）很容易让电荷通过，因为它们含有能够自由移动的电子。在电场中，这些自由电子会迅速重新分布，从而抵消导体内部的电场。这就是为什么在静电平衡下，金属物体的内部电场为零。

Insulators, on the other hand, do not have free charge carriers. Charges remain fixed where they are deposited, so insulating materials can hold a static charge and produce an external electric field. Examples include plastic, glass, and rubber. The build-up of static charge on insulators leads to common effects like sticking a balloon to a wall.

另一方面，绝缘体没有自由的电荷载流子。电荷会固定在沉积的位置，因此绝缘材料能够保持静电荷并产生外部电场。例子包括塑料、玻璃和橡胶。绝缘体上静电的积累会导致常见效果，比如气球贴在墙上。

6. Electric Field Around a Point Charge | 点电荷周围的电场

For a single positive point charge, the electric field pattern is radial and the lines point outward. For a single negative point charge, the field is also radial but the lines point inward. The field strength decreases with distance from the charge, which is shown by the lines spreading further apart.

对于单个正的点电荷，电场图样是辐射状的，并且场线指向外。对于单个负的点电荷，电场也是辐射状的，但场线指向内。场强随着离电荷距离的增大而减小，这表现为场线之间的距离越来越远。

The equation for electric field strength near a point charge is not required at GCSE, but you should recognise that the force on a test charge gets weaker as you move away from the source charge. This is similar to how light from a bulb appears dimmer further away.

点电荷附近电场强度的计算公式在 GCSE 阶段不作要求，但你应该认识到，检验电荷所受的力会随着远离源电荷而减弱。这类似于灯泡的光远处看起来更暗。

7. Electric Field Between Parallel Plates | 平行板间的电场

When two parallel metal plates are connected to a direct voltage supply, a uniform electric field is created between them. The field lines are straight, equally spaced, and point from the positive plate to the negative plate. This uniform field means the force on a charge placed anywhere between the plates is constant in magnitude and direction.

当两块平行金属板连接到直流电源上时，它们之间会产生一个匀强电场。电场线是等距的直线，方向从正极板指向负极板。这种匀强场意味着，放入两板之间任何位置的电荷所受的力大小和方向都是恒定的。

This arrangement is important in particle accelerators and in the old cathode ray tubes. A charged particle entering the region between the plates will accelerate towards the plate of opposite charge. The speed gained depends on the potential difference and the charge on the particle.

这种装置在粒子加速器和老式阴极射线管中非常重要。带电粒子进入两极板之间的区域后，会朝向异种电荷的极板加速。获得的速度取决于电势差和粒子所带的电荷。

8. Electric Field Strength | 电场强度

Electric field strength (E) is defined as the force per unit charge experienced by a small positive test charge placed at that point. It is a vector quantity measured in newtons per coulomb (N/C). The direction of the field strength is the same as the direction of the force on a positive charge.

电场强度（E）定义为放入电场中某点的微小正检验电荷所受的力与其电荷量的比值。它是一个矢量，单位为牛顿每库仑（N/C）。电场强度的方向与正电荷在该点受力的方向相同。

E = F / q

其中 E 是电场强度，F 是力，q 是电荷量。

where E is electric field strength, F is the force in newtons, and q is the charge in coulombs.

In a uniform field between parallel plates, the field strength is also related to the potential difference (V) and the plate separation (d) by the equation E = V/d. This gives an alternative unit of volts per metre (V/m), which is equivalent to N/C.

在平行板间的匀强电场中，电场强度也与电势差（V）和板间距（d）有关，公式为 E = V/d。这就给出了另一个单位伏特每米（V/m），它等同于 N/C。

9. Potential Difference and Electric Field | 电势差与电场

Potential difference (voltage) between two points is the work done per unit charge to move a charge between those points. In an electric field, moving a charge against the field direction requires work, which increases its electric potential energy. The stronger the electric field, the greater the potential difference over a given distance.

两点之间的电势差（电压）是将单位电荷从一点移到另一点时所做的功。在电场中，逆着电场方向移动电荷需要做功，这会增加电荷的电势能。电场越强，在给定距离内产生的电势差就越大。

In the uniform field between two parallel plates, the potential difference is directly proportional to the plate separation if the field strength is constant. This is why high voltages can cause sparks to jump across air gaps: the strong field can ionise the air and make it conductive.

在两块平行板间的匀强电场中，如果场强不变，电势差与板间距成正比。这就是为什么高电压能使火花击穿空气间隙：强电场可以使空气电离并使其导电。

10. Applications: Electrostatic Spraying | 应用：静电喷涂

Electrostatic spraying is used in painting cars and in crop spraying. The spray nozzle charges the paint droplets or pesticide particles as they leave. The object to be coated is given the opposite charge or is earthed. This ensures droplets are attracted to the surface, reducing waste and giving an even coating.

静电喷涂用于汽车喷漆和农作物喷洒。喷嘴在油漆雾滴或农药粒子离开时使其带上电荷。被喷涂的物体则带有相反的电荷或是接地的。这样可以确保雾滴被吸附到物体表面，减少浪费并使涂层均匀。

Since the charged droplets repel each other, they spread out into a fine mist before reaching the surface. This avoids large drops and helps cover awkward shapes. The same principle is used in inkjet printers to direct charged ink droplets onto paper using electric fields.

由于带电雾滴相互排斥，它们在到达表面前会散开成为细雾。这避免了形成大液滴，并有助于覆盖复杂形状。同样的原理用于喷墨打印机，利用电场将带电墨滴引导到纸上。

11. Applications: Electrostatic Precipitators | 应用：静电除尘

An electrostatic precipitator is a device that removes harmful particles from industrial flue gases before they are released into the atmosphere. As smoke flows up a chimney, it passes a strong negative electrode that charges the dust and soot particles. These charged particles are then attracted to positively charged collecting plates and stick to them.

静电除尘器是一种在工业废气排放到大气中之前去除有害颗粒的装置。当烟雾沿烟囱上升时，会经过一个强负电极，使灰尘和碳烟颗粒带上电荷。这些带电粒子随后被带正电的收集板吸引并粘附在其上。

The collecting plates are shaken periodically so that the accumulated dust falls into a hopper. This process cleans over 99% of the solid particles from the smoke, making a huge reduction in air pollution. The electric field is used to separate the particles without any physical filters that would clog up.

收集板定期受到振动，使积聚的灰尘落入料斗中。这个过程能清除烟气中超过 99% 的固体颗粒，大大减少了空气污染。电场被用来分离颗粒，无需任何会堵塞的物理过滤器。

12. Lightning and Safety | 雷电与安全

Lightning is a dramatic natural discharge of static electricity. During storms, ice particles in clouds collide and transfer charge. The top of the cloud becomes positive and the bottom negative. The negative charge on the cloud base induces a positive charge on the ground. When the electric field strength becomes great enough, it ionises the air, and a huge spark – lightning – travels between the cloud and the ground.

闪电是一种戏剧性的自然静电放电现象。暴风雨期间，云中的冰晶相互碰撞并转移电荷。云顶带正电，云底带负电。云底的负电荷在地面感应出正电荷。当电场强度足够大时，会使空气电离，一股巨大的火花——闪电——便在云与地之间传播。

To protect tall buildings, lightning conductors are installed. A metal spike at the top safely attracts the lightning strike and provides a low-resistance path to the ground, preventing damage. In everyday life, earthing straps allow static charges to flow safely away, for example when refuelling aircraft or vehicles.

为了保护高层建筑，安装了避雷针。顶部的金属尖端安全地吸引雷击，并提供一个通往大地的低电阻通路，防止损坏。在日常生活中，接地导线能让静电荷安全地流走，例如在为飞机或车辆加油时。

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Electric Fields | 电场