If you ask "Have you heard the word capacitor ", I believe everyone's answers are "heard", but if you ask "what is a capacitor", I think there should not be many people who can really answer it. For those who can’t answer or can only answer one or two, this article will allow you to submit a perfect answer!
Capacitor meaning
capacitor, simply put, it has two meanings, one refers to capacitor , that is, the actual circuit device; on the other hand, it refers to a certain parameter or effect, that is, capacitance parameters or capacitance effect.
From the name point of view, "capacitor" can also be interpreted as "the storage of charge (storage)" or "the storage of electric field energy (storage)". Therefore, in order to facilitate understanding of capacitors, it is necessary to know some knowledge about charges and electric fields.
, charge and electric field
Charge and electric field are accompanied by electric field. Charge, that is, particles with positive or negative charge, such as free electron , copper ion , etc. point charge (without a point of size and shape, only its charge amount is considered) is a typical charge model. As shown in Figure 1-1-1 below, these charges will excite the corresponding electric field around due to the existence of the charge. The more charges, the larger the electric field will be. This electric field will produce a force on other charges "placed in it", that is, homosexual charges repel each other and opposite charges attract each other. This force is electric field force .
Figure 1-1-1
The so-called "place it in it" means that other charges are placed within the range of the electric field. This is like the gravity field of the earth will have gravity effects on people on the surface of the earth. However, if people are far away from the earth, that is, they will float in the air due to the loss of the earth's gravity force. As shown in Figure 1-1-1, if the charge q2 approaches q1 until it contacts the electric field of q1, it will be subjected to the repulsive force of q1.
Similarly, if there is a copper metal plate, as shown in Figure 1-1-2 below, the positively charged copper ions inside it are leaning against the same side of the metal surface. At this time, these copper ions will stimulate an electric field on the surface of the copper metal, which is the synthetic electric field generated by these copper ions. If another piece of metal is close to the copper plate, then the free electrons inside the other piece of metal will gather on the surface close to the copper side under the attraction of the electric field force of the copper plate. In fact, this is the storage of charge, or in other words, this is the storage of electric field energy.
Figure 1-1-2
Imagine that if the copper ions on the surface of the copper metal plate in Figure 1-1-2 decrease, then the electric field excited on its surface will become smaller. At this time, the force of this electric field on the free electrons inside another piece of metal will also decrease accordingly. Therefore, the free electrons on the surface of another metal plate will also be reduced accordingly!
In addition, according to the nature of the electric field, the charge placed in the electric field will be affected by force. In other words, the electric field can do work on the electric charge, that is, the electric field has energy! The work done when the electric field force moves the unit positive charge from point A to point B is called the voltage of points A and B. This is also the potential difference of at points A and B. , as shown in Figure 1-1-3 below. This shows that voltage is a physical quantity that reflects the magnitude of the electric field between two points, and is also a reflection of energy.
Figure 1-1-3
According to the meaning of the capacitor: "the storage of charge (storage)" or "the storage of electric field energy" and combined with the above voltage definition, it is obvious that as long as the potential of is not equal, that is, there is a voltage, it indicates that there is an electric field. Then, the charge placed in the electric field will gather under the force of the electric field and have electric field energy. This phenomenon of generating charge accumulation and having electric field energy is called capacitance effect .
capacitance effect exists in many cases, such as between conductors of different phases, between phase lines and neutral lines, between phase lines and ground, between electrodes of diode , etc., because there is voltage between them, a capacitance effect will be generated.
See this, I believe everyone has a certain understanding of capacitors, but this is not the perfect answer! To master capacitor knowledge at a deeper level, "capacitors" are also an indispensable part.
capacitor
capacitor is a circuit device made based on the capacitance effect. It maximizes the capacitance effect and collects charges as much as possible, thus forming a large enough electric field and storing the corresponding electric field energy.
capacitors are widely used in engineering technology. They have a wide variety of types, models and specifications, but the structural principles are the same. Simply put, two metal plates close to each other have a layer of non-conductive insulating medium (such as insulating paper , mica, air, etc.), which forms a capacitor, as shown in Figure 1-1-4 below.
Figure 1-1-4
When a voltage is applied between the two metal plates of the capacitor, that is, an external electric field is applied. Under the force of this external electric field, the charge of the metal plate gathers, for example, the metal plate connected to the external voltage positive electrode (power supply positive electrode), and its positive charge gathers in the direction between the two plates due to the repulsive force. Similarly, the negative charge of the other metal plate also gathers in the direction between the two plates.
With charge aggregation, an electric field is established between the two metal plates of the capacitor, that is, a certain electric field energy is stored, which is the energy storage property of the capacitor. In a word, the energy absorbed by the capacitor is stored in the electric field between the plates in the form of electric field energy.
capacitors are widely used and play different roles in different circuits, such as coupling , filtering, rectifying, reactive compensation , etc. To understand the different functions of capacitors, we have to understand the relevant characteristics of capacitors, that is, its circuit analysis .
capacitor components and their parameters
capacitor components and capacitors have two words: capacitor. So is there any difference between them? Are capacitor components capacitors? Let's take a look together.
, capacitor element
capacitor modeling in circuit analysis is capacitor element. capacitor element is an ideal component. It only reflects the physical phenomenon that the capacitor can store charge (storage electric field energy). Its circuit symbol is two short vertical lines, as shown in Figure 1-1-5 below. These two short vertical lines are like two metal plates, which can be said to be very vivid.
Figure 1-1-5
The above mentioned "ideal component". What does "ideal" mean here? In fact, it refers to ignoring other factors of the actual capacitor. For example, in addition to the role of energy storage in the circuit, actual capacitors will also generate certain electrical energy losses. The loss of this electrical energy is equivalent to the role of resistance, that is, actual capacitors also have the characteristics of partial resistance. However, the capacitor element obviously does not have a resistor and cannot reflect the energy loss, so this is the difference between a capacitor element and a capacitor.
But in fact, we often call actual capacitors capacitance components. Based on this, everyone must understand the specific problems of to analyze in detail. For example, if the power loss of the capacitor cannot be ignored, then its modeling in circuit analysis should be a parallel combination of capacitor elements and resistive elements, as shown in Figure 1-1-6 below. However, if its power loss is ignored, the modeling of the capacitor can be directly represented by capacitor elements.
Figure 1-1-6
Since the capacitor element reflects the energy storage properties of the capacitor, it must express the stored energy in some way. This is the origin of "capacitor C ".
Charge stored in capacitor component q and voltage u has a certain algebraic relationship, that is, the charge stored on the plate of the capacitor element q is proportional to the voltage across it. This is the component characteristics of the capacitor element. The proportional coefficient of the is with the letter "C ” represents, as shown in Figure 1-1-7 below.
Figure 1-1-7
Figure 1-1-7 shows that q =C " in C is the parameter of the capacitor element, called capacitor, and is a positive real constant. That is to say, a specific capacitor component has a capacitance C is a constant greater than zero (the number whose value remains unchanged) that does not change with the change of external conditions.
Obviously, the capacitor C is the ratio coefficient of charge to voltage. Using the voltage u as the horizontal coordinate and the charge q as the vertical coordinate, the characteristic curve of the capacitor element can be drawn. As shown in Figure 1-1-7, this curve is called the Kuvol curve, and the slope is the capacitor C .
As for why it is called a Kuvol curve, it is very simple, because the unit of charge q is Coulomb , and the unit of voltage u is volts, so this curve is called a Kuvol curve.
When the unit of charge q is coulomb and the unit of voltage u is volts, the unit of capacitor C is Farah, denoted by the letter "F", referred to as method. 1F is actually a very large number. In many cases, its units appear in the form of "μF (micromethod)" and "pF ( picomethod )". Their relationship is shown in Figure 1-1-8.
Figure 1-1-8
capacitor element parameters are called capacitors, but generally, for convenience, we also call capacitor elements capacitors. In other words, the word "capacitor" and the symbol "C " represent the capacitor element on the one hand and the parameters of the capacitor element on the other hand.
More about capacitors, such as the difference between capacitor components in AC circuit and DC circuit , what is capacitance resistance related to capacitors, etc. We will explain it in the next article, please continue to pay attention!
(Source: Original from Qicheng Training Network, author: Yang Sihui, reprinting is not allowed without authorization, violators will be prosecuted!)
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