导体和绝缘体
当人们脱下合成服装或毛衣时，尤其是在干燥的天气里，他或她经常会看到火花或听到噼啪声。对于像涤纶纱丽这样的女性服装，这基本上是可以观察到的。另一个例子是闪电，一种常见的放电形式，在雷暴期间在天空中看到，打开车门或从座位上滑下后抓住公共汽车的铁条时会产生触电的感觉。
这些感觉的原因是由于摩擦绝缘表面而收集的电荷的放电。这与静电产生有关。任何不随时间移动或变化的东西都称为静态的。对来自静电荷的力、场和电势的研究称为静电学。
导体
手上刷有羊毛的金属棒不会有任何带电的迹象。另一方面，带有木柄或塑料柄的金属棒在不接触其金属部分的情况下用羊毛摩擦时会出现带电症状。假设铜线的一端连接到中性髓球，另一端连接到带负电的塑料棒。观察到髓球将获得负电荷。当用尼龙线或橡皮筋进行类似的实验时，没有电荷从塑料棒转移到髓球。
Some materials readily enable electricity to pass through them, whereas others do not. Conductors are materials that allow electricity to flow freely through them. They have comparatively free-moving electric charges (electrons) inside the material. Conductors include metals, human and animal bodies, and the ground itself.
电路和设备受益于作为安全措施的接地。一块大金属板深深地埋在土里，从中拖出粗大的电线；这些电缆用于靠近电源的建筑物接地。我们家的电线由三根电线组成：火线、零线和地线。前两个承载来自发电厂的电流，而第三个通过连接到埋地金属板而接地。地线连接到电熨斗、冰箱和电视机等电气设备的金属体上。当发生故障或火线与金属体接触时，电荷流向大地，不会损坏电器或伤害人体；否则这将是不可避免的，因为人体是电导体。
导体的应用
导体在各种情况下都非常方便。它们在各种情况下都很有用。举个例子，
- 汞是用于测量体温的温度计的常见成分。
- 铝用于制造食品储存箔。它还用于制作可以长时间保温的煎锅。
- 铁是汽车发动机生产中使用的典型导热材料。
- 铁板由钢制成，可快速吸收热量。
- 汽车散热器中使用导体将热量从发动机中转移出去。
导体示例
- 银是最有效的电导体。然而，由于银价格昂贵，它不用于工业或能源传输。
- 铜、黄铜、钢、金和铝是优良的电导体。我们以电线的形式在电路和系统中使用它们。
- 水星是液体的良导体。因此，这种材料被用于各种仪器中。
- 由于原子相距甚远，气体是电的不良导体。结果，它们不能传导电子。
绝缘子
Most non-metals, such as glass, porcelain, plastic, nylon, and wood, have a high resistance to the transmission of electricity. They are called insulators. Insulators are materials that prevent electrons from freely flowing from one element’s particle to another. If a charge is applied to such an element at any point on the surface, the charge remains in the same place and does not spread throughout the surface. Charging by rubbing (for some elements, with the help of suitable materials) and charging by induction are two typical methods for charging such components.
当电荷传输到导体时，它会迅速带电。分散在导体的整个表面上 如果另一方面，一些电荷施加到绝缘体上时，它会保持静止。这种材料特性解释了为什么首选尼龙或塑料梳子。梳理干燥的头发或抚摸它时，它会带电，而金属片则不会。金属上的电荷通过我们的身体到达地面。地面和身体都是电导体。
绝缘子的应用
- 世界各地都在使用绝缘体，因为它们可以防止电子流动。最常见的应用包括：
- 热绝缘体可防止热量从一个位置移动到另一个位置。因此，他们习惯于制造热塑性塑料瓶。它们还用于防火墙壁和天花板。
- 隔音材料可用于控制噪音水平，因为它们可以很好地吸收声音。因此，我们使用它们使建筑物和会议空间无噪音。
- 电绝缘体阻碍通过它们的电子流动和电流流动。因此，我们经常在电路板和高压系统中使用它们。电线和电缆也涂有它们。
绝缘子的例子
- 由于其高电阻率，玻璃是最好的绝缘体。
- 塑料是一种很好的绝缘体，用于制造各种物品。
- 橡胶通常用于制造轮胎、防火服装和鞋子。这是因为它是一种极好的绝缘体。
导体和绝缘体之间的区别。
Conductor | Insulators |
|---|---|
A conductor is a material that permits current to flow freely through it. | Insulators prevent current from flowing through them. |
Electric charge exists on the surface of conductors. | Electric charges are absent in the insulator. |
Conductors don’t store energy when kept in a magnetic field. | Insulators store energy when kept in a magnetic field. |
The thermal conductivity ( heat allowance) of a conductor is very high. | Insulators store energy when kept in a magnetic field. |
Conductors don’t store energy when kept in a magnetic field. | Insulators store energy when kept in a magnetic field. |
The thermal conductivity ( heat allowance) of a conductor is very high. | The thermal conductivity of an insulator is very low. |
The resistance of a conductor is very low. | The resistance of the insulator is very high. |
示例问题
问题 1：摩擦充电是什么意思？
解决方案：
The charging by friction method includes rubbing one particle against another, causing electrons to move from one surface to the next. This procedure can be used to charge insulators.
Different types of atoms and atom combinations make up material objects. Various items have different electrical characteristics due to the existence of different atoms in them. Electron affinity is one of these properties. Simply described, electron affinity is a feature that describes how much a substance cares about electrons. If a substance’s atoms have a high electron affinity, the material will have a strong affection for electrons as well. As one of the most prevalent types of charging, turboelectric charging, commonly known as charging by friction or rubbing, this property of electron affinity will be crucial.
问题 2：如果每秒有 10 9 个电子从一个物体移动到另一个物体，那么需要多少时间才能在另一个物体上获得 1 C 的总电荷？
解决方案：
In one second 109 electrons move out of the body. Therefore, the charge given out in one second is
1.6 × 10–19 × 109 C = 1.6 × 10–10 C.
The time required to accumulate a charge of 1 C can then be estimated to be
1 C / (1.6 × 10–10 C/s)
= 6.25 × 109 s = 6.25 × 109 / (365 × 24 × 3600) years
= 198 years.
Thus, to collect a charge of one coulomb, from a body from which 109 electrons move out every second, we will need approximately 200 years. One coulomb is, therefore, a very large unit for many practical purposes. It is, however, also important to know what is roughly the number of electrons contained in a piece of one cubic centimeter of material. A cubic piece of copper of side 1 cm contains about 2.5 × 1024 electrons.
问题3：纯净水会导电吗？如果没有，我们能做些什么来让它导电？
解决方案：
No, pure water doesn’t conduct electricity. When salt is dissolved in pure water, it conducts electricity as it provide it with ions needed to conduct electricity.
问题4：一杯水有多少正负电荷？
解决方案：
Let us assume that the mass of one cup of water is 250 g. The molecular mass of water is 18 g. Thus, one mole (= 6.02 × 1023 molecules) of water is 18 g. Therefore, the number of molecules in one cup of water is (250/18) × 6.02 × 1023. Each molecule of water contains two hydrogen atoms and one oxygen atom, i.e., 10 electrons and 10 protons. Hence, the total positive and total negative charge has the same magnitude. It is equal to
(250/18) × 6.02 × 1023 × 10 × 1.6 × 10–19 C
= 1.34 × 107 C.
问题 5：什么是库仑定律？
解决方案：
According to Coulomb’s law, the force of attraction or repulsion between two charged things is directly proportional to the product of their charges and inversely proportional to the square of the distance between them. It acts along the line that connects the two charges that are regarded to be point charges.
Coulomb studied the force between two point charges and found that it is inversely proportional to the square of the distance between them, directly proportional to the product of their magnitudes, and acting in a line that connects them.