For this course, the secret to truly understand and master is to keep thinking. I think this is the most important point. I take Jiang Jiguang's circuit principle as an example to explain why I can't stop thinking.
Circuit is almost the first book to cultivate your engineer thinking. It is different from mathematical physics, and many of them can be deduced theoretically. And the circuit is more about your thinking and accumulated experience.
In Jiang's book, the first four chapters explain the basic knowledge of resistance circuits, including reference direction, substitution theorem, branch method, node voltage, loop current, Thevenin, Tellegen and reciprocity theorem. These basic contents must be memorized before they can be used flexibly in later chapters. How can I recite it? I always remind myself to keep thinking. The after-class exercises in this textbook are the best treasure house to stimulate your brain's thinking ability. It can be said that every question in it is highly targeted and the topic is not difficult.
A qualified engineer should spend more time thinking about how to solve the problem most reasonably, instead of spending a lot of time calculating. The calculation of the circuit is very large, and a node voltage equation group may be a quartic equation. Obviously, these things should be left to the calculator. In order to learn the circuit well, you should buy a Casio 99 1 to save unnecessary time and think about the problem itself.
The foundation of the first four chapters must be very solid, not only can use, but also can't learn the circuit well. You should carefully study how each theorem comes from, and you'd better prove it yourself. You should know that Thevenin is derived from superposition, and the superposition theorem is unchanged when the resistance circuit is linear, and the reciprocity theorem is derived by Tellegen. This knowledge is accumulated little by little. At first, you will feel confused when you see them, but you have to believe that this is a process, and gradually you will find the circuit wonderful and even fall in love with it. When you find an answer that can be solved on one page, it can be solved in only five or six lines, and then you will feel as if the circuit is flowing out of your body. This is the realm that has been pursued.
Then there is nonlinearity. This chapter is not very demanding in many schools, and it is not difficult to test. If you are most interested, learning is very interesting.
Then first-order and second-order dynamic circuits. Learn high differential equations well, and high school circuit knowledge can be solved. The essence of this part is to solve differential equations.
To put it bluntly, you need circuit knowledge to list differential equations according to circuits, and how to solve the rest depends on your mathematical skills. However, in order to reduce our pressure, the circuit teacher took out the first-order circuit and made a special topic, summarizing everything about the current or voltage of each branch on it with a simple conclusion, that is, the three-factor method.
Learning three-element first-order circuits doesn't even use column equations. As long as we know the initial state, final state and time constant of the circuit, we can get the result. If you are willing to think, in fact, the second-order circuit can also be compared with it. In the second-order circuit, as long as the time constant, initial value and final value are found, the general solution can also be found.
At the end of this part, a good integral-convolution is introduced. Many people will be fooled by his name, and it is very high-tech to mention it. In fact, it is really high-tech, but as long as you master its essence and use it well, it will greatly improve your circuit thinking. There are many good explanations and vivid examples about convolution in Zhihu and Baidu, and I also used them for reference. I can only remind you here, don't ignore convolution because the teacher didn't focus on it, otherwise it would be tantamount to losing a sword. I remember when I was studying Duamel integral (a kind of convolution), I felt that I was a treasure, although there was only one sentence in the book. But for that sentence, I can't be calm for a long time, because it is so easy to use.
Next is the sine circuit, where the transformation of the circuit is mainly understood from the time domain. Here is the first sublimation of the circuit. The great human beings hit a point on the communication head with their own wisdom, and then everything returned to calm, followed by the knowledge of the first four chapters. I think he uses the principle that all quantities are changing at a frequency, and the effect is almost the same at rest, but it has a new influence on capacitance and inductance, because there is a differential and integral relationship between their current and voltage. Under the new idea, you can change the inductance to jwl and the capacitance to 1/jwc, and then you can think about why you can change it like this.
This is the relationship between current and voltage in polar coordinates can be deduced. You have to go back to the source and say, why can you use complex numbers instead of sine? That's because Euler's formula transforms sine into complex expressions. What is Euler's formula? It is derived from mclaughlin formula. You have to keep thinking and asking questions to understand what is going on.
However, this is the foundation. Sinusoidal steady state, the essence here is to draw a vector diagram. Only by drawing the vector diagram correctly can we really understand it. Vector diagram is not graffiti. You can't just find a branch and put it horizontally to get the correct picture. Sometimes you can't get the right answer if you go wrong, but you may fall into the whirlpool of thinking. The vector diagram generally takes the branch with resistance or the branch with resistance as the horizontal vector, and then advances step by step according to its current and voltage. Moreover, many problems hide a lot of information in the picture, and you can't solve them without drawing a good picture. This also needs to be thought out by yourself.
Learn from teacher Zhang Fei.
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Behind it is mutual feelings. I believe many people were tortured to death by the same name. In fact, inductance is a quantity that describes the ability of a coil to establish a magnetic field. The greater the inductance, the greater the magnetic field. Therefore, the terminal with the same name means that the current flowing in from the terminal with the same name is added with the magnetic field, which is expressed as inductance addition in the equation. As long as you keep this in mind, it is not wrong to list equations with mutual inductance. Don't be paranoid, sometimes you will be confused by the direction of the current. Leave it alone. The picture shows the reference direction. Even if your hypothetical direction is opposite to the actual direction, it still has no effect on the real result. This is actually to examine your understanding of the reference direction.
Then there is resonance, which is a very interesting and useful plate, which is indispensable for electricity, communication, analog electricity and high voltage. This is the perfect alternation of power plant energy and station energy in a wonderful state. Through resonance, practical circuits such as filtering and boosting can be realized. But as far as the circuit content is concerned, it is not difficult here. To sum up, zero imaginary part of impedance means series resonance, and zero imaginary part of admittance means parallel resonance. Sometimes it is more convenient to solve the resonance frequency with admittance, because it is more convenient to do more problems and broaden your mind.
Next is the three-phase circuit. For me, the three-phase circuit is the simplest part. Many people find it difficult (of course, I felt dizzy at first) simply because we are always afraid of fear itself. Actually, you see, it has three places, but it's not difficult at all. This requires you to be clear-headed and don't be scared by his appearance. Three-phase circuit is no different from ordinary circuit. You won't be afraid to realize five or six power supplies, because you know that a circuit in which all components are informed can definitely be found by node voltage or loop current. Why are you frightened out of my wits at the third stage? Do you not understand the relationship between line voltage and phase current, or the influence of one-phase disconnection on neutral current? What do you care about this? What pictures, lines, etc. It's just a code name You think of it as an ordinary circuit solution, it is just an ordinary circuit. Many students always like to struggle with the relationship between online and phase. In fact, it can be summarized in one sentence: the line quantity is three times the square root of the vector. In fact, you don't need to remember all this. Just draw a picture when necessary. The most important thing is to understand that three-phase electricity is just an ordinary circuit with three power supplies. As long as you know the node voltage method, you can solve it well without learning the knowledge of three phases. When you look at it with a normal circuit, you already know three stages. The only difficulty of three-phase is calculation. As long as you are a careful person, it is difficult to find more problems to calculate in the future.
Followed by Laplace transform. This is another leap in circuit thinking. It is found that high-order circuits are really difficult to solve. If the power supply changes, there is no better way than convolution. Therefore, in order to facilitate the use of convolution, the predecessors introduced Laplace transform into the circuit. If Taylor formula is used to deduce sine steady-state time domain to frequency domain step by step. Then this is the last chapter of high numbers-Fourier transform. There are also many wonderful explanations about Fourier branch Hu. Find it yourself. Fourier transform has two forms, one in time domain and the other in frequency domain. Laplace transform extends Fourier transform from frequency domain morphology to complex frequency domain morphology. Its basic transformation formula is also extended from Fourier transform formula. In this chapter, you should start with the transformation formula and deduce several basic transformations yourself. It is also necessary to understand the final value theorem and the initial value theorem, which is strong evidence to test whether the results are correct or not. It's one thing to learn the circuit and only know the way of thinking, but it's another thing to do it right. Only by constantly cultivating their broad horizons and strong computing ability can we learn this course well. Learning circuit depends on hard work. Watching the teacher solve the problem, you feel comfortable, but you are puzzled. That's not enough kung fu. I read the circuit of 100 days during the postgraduate entrance examination, and all the new books were rotten. My old books are falling apart, at least I did the exercise of 1500, and there is no repetition. When I do the circuit, I feel that time has stopped and I don't feel that there are others in the study room. The happiness that you finally solved a problem after thinking hard is enough to make you laugh. It is the best medicine to accompany me. Walking in the moonlight every day, I think, if you can't be a scientist, then do something else.
Therefore, if you want to learn the circuit well, you still have to fall in love with it from the heart.
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