22.3
导体和绝缘体
有些材料很容易让电荷通过，而另一些材料则阻碍电荷的流动。 前者称为导体，后者称为绝缘体。 材料的原子结构决定了它们是电的导体还是绝缘体。
大多数金属都是导体。 它们的原子结构使得一个或多个电子松散地结合到每个原子的原子核上。 因此，其中有大量的移动电子，称为自由电子。 它们的轻松移动可以中和添加到导…
原子由带正电的原子核和围绕其运动的电子组成，电子形成电子云。带正电的原子核与电子之间通过相互吸引的电作用力结合在一起。
在某些材料中，电子与原子核的结合较为松散。例如，一个铜原子包含29个质子和29个电子。然而，其中一个电子与原子核的结合较弱，可自由移动。
自由电子的总数等于导线中原子的总数，这些电子可以在整个导线中自由移动。因此，当外部电荷源与铜接触时，电子会迅速通过导线移动。大多数金属（如铁、金和银）能够导电，被称为导体。
然而，木材、玻璃、纸张和丝绸等材料没有自由电子。它们的原子结构使得所有电子都牢固地与原子核结合。因此，这些材料无法传导电荷，被称为绝缘体。
因此，当它们相互摩擦而带电时，多余的电荷会保留在其表面，从而产生静电力。
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Q1: Why do some materials conduct electricity while others don't?
A material's ability to conduct electricity depends on its atomic structure. Conductors like copper have loosely bound electrons that move freely throughout the material, forming a sea of mobile electrons. Insulators like glass and wood have all electrons firmly bound to their nuclei, preventing electron movement. This structural difference determines whether charges can flow through the material.
Q2: What are free electrons and how do they relate to conductivity?
Free electrons are electrons loosely bound to atomic nuclei that can move throughout a material. In conductors like copper, one electron per atom is free to move, creating a mobile electron population equal to the total number of atoms. These free electrons enable rapid charge movement when external charge contacts the conductor, making the material an effective conductor of electricity.
Q3: How do insulators behave differently from conductors when charged?
When insulators are charged, excess charges remain stationary on the material because electrons cannot move freely between atoms. This charge accumulation creates electrical forces between insulators or with other charged materials. Conductors, by contrast, neutralize external charge through rapid electron movement, preventing excess charge accumulation and eliminating mutual electrical forces.
Q4: Why does touching a charged doorknob after walking on carpet cause an electrical shock?
Walking on carpet, an insulator, causes excess charges to accumulate on your body because the insulator's electrons cannot move freely. Your body acts as a conductor, holding these charges. When you touch a charged conducting object like a doorknob, the accumulated charges rapidly flow through you to the conductor, creating the shock sensation.
Q5: Which metals are good conductors of electricity and why?
Most metals, including copper, iron, gold, and silver, are excellent conductors because their atomic structures feature loosely bound electrons. Each atom contributes one or more free electrons that form a mobile electron sea throughout the material. This abundance of movable electrons allows charges to flow rapidly through the metal when an external charge is applied.
Q6: What are common examples of insulators and their properties?
Common insulators include wood, glass, paper, silk, plastic, and fur. These materials share a key property: all their electrons are firmly bound to atomic nuclei, preventing free electron movement. Because electrons cannot move between atoms, any excess charge added to insulators remains localized on the material, leading to charge accumulation and electrical forces.
Q7: How does the atomic structure of copper make it an effective conductor?
Copper atoms contain 29 protons and 29 electrons, with one electron loosely bound to the nucleus. This loosely bound electron is free to move throughout the copper wire. The total number of free electrons equals the total number of atoms in the wire, creating an extensive mobile electron population that enables rapid charge movement when external charge contacts the copper.