电介质和极化
您是否注意到有多少绝缘体是由木头、塑料或玻璃制成的？但这是为什么呢？当我们使用木材或塑料时，为什么我们不会受到电击？为什么你只会受到金属线的严重冲击？我们将在本章中研究电介质、极化、介电常数等。我们还将介绍这些电介质的一些典型应用和示例。
什么是电介质？
Non-conducting materials are known as dielectrics. They are insulating materials and poor electric current conductors. Dielectric materials can maintain an electrostatic charge while losing very little energy as heat. Mica, plastics, glass, porcelain, and other metal oxides are examples of dielectrics. It’s also important to note that even dry air is dielectric.
电介质分类
电介质有两种类型：
- 极性分子：极性分子是那些正负分子碰撞机会为零或零的电介质。这是因为它们在形式上都是不对称的。 H 2 O、CO 2 、NO 2和其他气体是示例。当没有电场时，这些分子的电偶极矩会朝着不可预测的方向移动。因此，平均偶极矩为 0。如果有外部电场，分子将按照与电场相同的方向聚集。
- 非极性分子：与极性分子不同，非极性分子中正负电荷的中心不重合，即为零。分子中不再有任何持久的（或固有的）偶极矩。例子包括O 2 、N 2 、H 2等。
感应电偶极矩
当对非极性分子施加外部电场时，所有质子都沿与电场相同的方向运动，而电子则沿相反方向运动。除非由于电场的存在而使内部压力平衡，否则该过程将继续。这导致形成两个电荷中心。我们将它们命名为感应电偶极子，因为它们是极化的。感应电偶极矩是偶极矩。
极化率
When the matter is exposed to an electric field, it has a propensity to develop an electric dipole moment that is proportional to the applied field. Because matter is made up of fundamental particles with an electric charge, such as protons and electrons, it is a property of all matter.
带负电的电子和带正电的原子核受到相反的力，并在暴露于电场时经历电荷分离。介电常数和在高（光学）频率下，材料的折射率由其极化率决定。
施加的场与感应偶极矩成正比并且与温度无关。对于单个极性原子，感应偶极矩 (x) 的方向平行于电场 E 的方向。束缚系统的极化率影响其对外部场的动态响应。
它还提供有关分子内部结构的信息。极化率是固体的定义为每单位体积晶胞的偶极矩：
P = ε 0 α E
其中α是原子极化率，E是电场。
它的SI单位是m3，它的尺寸和它的体积一样。
电极化
When a dielectric slab is placed in an electric field, the molecule acquires a dipole moment. In such circumstances, the dielectric is said to be polarised. The Electric Polarization of a dielectric substance is the dipole moment per unit volume. P is the symbol for polarisation.
介电常数
介电常数是在平行板之间放置电介质板时施加的电场强度与电场电容器减小值的强度之比。公式如下：
ε r = E 0 / E
其中 E 0是施加的电场，E 是净场，& ε r是介电常数。
介电常数越大，可以保持的电荷量就越大。当极板之间的间隙完全被电介质填充时，电容器的电容会增加一个介电常数因子。 C = ε r C0，其中 C0 是没有电介质的板之间的电容。
Dielectric Strength
The dielectric strength of insulating material is the highest electric field strength that it can tolerate intrinsically without losing its insulating characteristics.
介电极化
Dielectric Polarization occurs when an external electric field is applied to a dielectric substance. When an electric field is applied, it causes charges (both positive and negative) to be displaced. The primary goal of dielectric polarisation is to connect macroscopic and microscopic characteristics.
在压电晶体的情况下，极化是由电场或其他外部变量（如机械应力）的作用引起的。收集电荷的固体材料称为压电晶体。
介电 在热释电晶体中，极化也可以自发发生，尤其是在铁电体中。铁电性是一些材料的一个特征，其中自发电极化可以通过施加电场来逆转。
极化公式如下：
P = ε 0 × e E = ε 0 (ε r - 1) E
其中 P 是极化，χ e是磁化率，& E 是电场。
示例问题
问题 1：电容器内部的电场为 50 V/m，介电常数 = 4.5。什么是极化？
回答：
Given:
Dielectric Constant, εr = 4.5
Electric Field, E = 50 V/m
Susceptibilty, χe = εr − 1 = 4.5 − 1 = 3.5
Polarization, P = χe E
= 3.5 × 50
= 175 C/m2
Hence, the polarization is 175 C/m2.
问题2：什么是介质极化？
回答：
When an external electric field is applied to a material, dielectric polarisation is the term used to describe its behaviour. An externally applied electric field causes a dipole moment to develop in an insulating material, which is known as dielectric polarisation.
When a current interacts with a dielectric (insulating) substance, the dielectric material shifts its charge distribution, with positive charges aligning with the electric field and negative charges aligning with the electric field. Important circuit components like capacitors may be manufactured by taking use of this reaction.
问题3：聚苯乙烯的相对介电常数为3.5。当 1.5 mm 厚的聚苯乙烯片材承受 240 V 电压时会产生什么极化？
回答：
Given that,
Dielectric constant,
εr = 3.5
ε0 = 8.85 × 10−12 C / V m
Thickness, d = 1.5 mm = 1.5 × 10−3 m
Voltage, V = 240 V
Electric Field, E = V/d
= 240 / (1.5 × 10-3) V/m
= 1.6 × 105 V/m
Polarization, P = ε0 (εr − 1) E
= 8.85 × 10−12 × (3.5 – 1) × 1.5 × 105 C/m2
= 3.32 × 10−6 C/m2
Hence, the polarization produced in polysterene is 3.32 × 10−6 C/m2.
问题 4：解释绝缘体及其特性？
回答：
Insulators are materials that make it difficult for electric charges to flow freely. The outer shell electrons are firmly linked to the nucleus in the atoms of such substances. These chemicals have a high impedance to the passage of electricity because they lack free charge carriers. Glass, diamond, porcelain, plastic, nylon, wood, mica, and other non-metals are all insulators.
Properties:
- Insulators have a poor conductivity and a high resistance.
- Their atoms contain electrons that are firmly bonded and do not migrate throughout the substance.
- A current cannot readily flow because the electrons are stagnant and not freely moving.
问题5：什么是介电材料？
回答：
Dielectric materials are insulating materials that are poor conductors of electric current. When a dielectric is put in an electric field, it shows an electric dipole, which means that positive and negative electrically charged entities are separated on a molecular or atomic level. Capacitors, power lines and electric insulation switch bases, and light receptacles all employ them.