Because electromagnetic waves are transmitted in the wire is a mode of electromagnetic waves Spreading in a vacuum is also a pattern They are solutions of Maxwell's equation under certain boundary conditions The frequency of electromagnetic wave propagation is the characteristic value of the equation The distribution of magnetic field in an electromagnetic field is the characteristic vector of the equation All this can not escape the wisdom of Maxwell ~ Multitasking: The wire is to bind electromagnetic waves, not to bind electrons. For electromagnetic waves of different frequencies, waveguides of different materials are required. Electromagnetic wave propagation does not depend on the medium, and the role of the wire is to control the direction of propagation. Loki: Take a pit first and wait a few days to return to electrodynamics Briefly answer the question: 1. Why can the wire confine the electromagnetic wave? First of all, not all wires can bind electromagnetic waves. After the electromagnetic wave frequency comes, the general wire cannot hold at all. From the derivation of the waveguide equation, the relationship between dissipation and electromagnetic frequency can be found (see the figure below). To understand it briefly, it is because of the existence of boundary conditions that the electromagnetic waves are reflected back and forth between the walls of the pipe (hence the restriction) and then propagated. 2. No medium is needed for electromagnetic wave propagation. Why is the wire? It is true that the propagation of electromagnetic waves is different from that of mechanical waves and does not require any medium (the mere ether hypothesis does not hold). However, the presence of media can affect the transmission of electromagnetic waves! It is precisely because of this characteristic that by using a reasonable choice of materials (both metals and insulators) to make the wire, high-frequency electromagnetic wave signals can be transmitted with controlled dissipation. In other words, the presence of transmission lines can help with high-frequency signal propagation. Secondly, when considering the transmission of signals on the transmission line, especially in the optical fiber, we must especially consider the refractive index of the medium. If the subject is studying excessive sub mechanics, it should be known that the refractive index is related to the density of states (DOS). Therefore, the transmission line is not only needed but also necessary. After all, compared to the five slags of vacuum or air, the density of states contained in the optical fiber (mainly composed of SiO2) is high. To put it aside, this is also the principle that solar cells generally use Silicon to absorb photons. Temporarily think of these, and then make up for formula derivation. Spirit Sword: Electromagnetic wave propagation does not require media ç”µç£ Electromagnetic waves cannot propagate in media Electromagnetic wave propagation does not require media ≠Medium does not affect electromagnetic wave propagation Strictly speaking, for the distribution parameter circuit, the medium that propagates electromagnetic waves includes both the wires and the space between the wires. For example, inserting a core in an inductor can affect the circuit parameters, indicating that the iron core is also part of the medium through which electromagnetic waves propagate. ================================================== === Looking at the other answers, I think whether or not there is a reply, that is, what is the role of the wire? A: The wire can restrain the electric current, which also confines the electric field generated by the electromotive force to a certain extent, but it can not bind the magnetic field, nor can it restrain the induced electric field generated by the magnetic field. The principle of the electric wire that constricts the electric field generated by the electromotive force is that it can conduct electricity, that is to say, by the effect of the bound current. The conductor generates electric current in the presence of electromotive force. The current can only flow along the conductor. The current flowing through the conductor with resistance generates a potential difference, so that the potential is fixed along the conductor. In the steady field, the electric field is the gradient of potential. Followed by the electric potential is tied up. However, the magnetic field is not controlled by the conductor. The magnetic field generated by the current will spread out in the vertical direction. If it is a changing magnetic field generated by an alternating current, this magnetic field will continue to excite the electromagnetic wave, and the electromagnetic wave will propagate outside the conductor. This leakage will change the impedance characteristics of the conductor and reduce the transmission efficiency. In order to prevent such leakage, the common practice is to offset each other with an opposite field, so that the electromagnetic waves cannot run outside. For example, twisted pairs, the currents on the two lines are opposite, and the magnetic fields cancel each other, and the electromagnetic waves radiate. Do not go out, but this is not the conductor bound electromagnetic waves, electromagnetic waves will still spread in the gap between the two lines. This should be divided into two situations to discuss: DC and AC For DC power, voltage is established across the wire, an electric field is generated inside the wire, and the electrons move to cause a current, which is no problem. For the current I, its definition is also In this case, there is no electromagnetic wave, and the electric field established in the conductor plays a major role in transmission. Otherwise, with the slow movement of free electrons, assuming that the wire is a few hundred kilometers long, it takes a long time to stimulate the signal at one end and receive the signal at the other, which is obviously impossible. -------------------------------------------------- ------------------------------ For alternating current, the electric field inside the wire is a changing electric field, and the changing electric field produces a changing magnetic field, which generates electromagnetic waves. In fact, the wire does not confine the electromagnetic wave. The reason why the wire is able to trap electromagnetic waves at low frequencies is because the frequency of the electromagnetic wave is too low at low frequencies. The wavelength of the electromagnetic wave is too long, and energy cannot be effectively radiated. (Of course, it is not impossible. Radiation is simply because the proportion is too small and can be ignored in the case of low energy.) Take AC 50Hz as an example, the wavelength is It is about 6000km. Obviously for most domestic wires, the length and the wavelength of the alternating current are not at an order of magnitude at all, so there is basically no energy to radiate. Even for FM broadcasting (around 100MHz), the wavelength is about 3m. According to the antenna theory, an antenna of at least 30cm in length is required to radiate electromagnetic waves effectively, so you can see that there are generally huge antennas for broadcasting stations. Yufa signal (although it is mainly the size of the pot, but the antenna itself is not small) When the frequency reaches the GHz level (wavelength is only tens of centimeters), the electromagnetic wave radiation is actually very easy. The RF circuit is difficult to do because the circuit has a wide pass band, and the external high-frequency signal is easily coupled to the circuit. , is very susceptible to interference. In the RF circuit design, in order to effectively transmit electromagnetic waves, a waveguide such as a metal waveguide/coaxial line/microstrip line is required to conduct electromagnetic waves, and electromagnetic radiation is avoided by a specially designed electric field structure, and a non-main mode is made as possible as possible. Cut-off, to maximize the guidance of the main mode of electromagnetic wave propagation, the other reason is that the skin effect of the wire is also very serious at high frequencies, electromagnetic waves are difficult to conduct along the wire (all become heat loss). In the example of a coaxial cable, this is the electric field and magnetic field distribution of the coaxial line (from Baidu Encyclopedia It can be clearly seen that the electric and magnetic fields are mainly distributed between the two conductors instead of the inside of the conductor. In fact, in the case of relatively high frequencies, there is almost no electric field inside the conductor. The specially designed electric field structure of the coaxial line can also ensure that electromagnetic waves transmitted within it will hardly radiate as long as the cutoff frequency is not reached. So, here the electromagnetic wave is mainly transmitted through the medium between two layers of conductors (a vacuum is not impossible). From a certain point of view, the significance of the wire/waveguide is to provide the boundary conditions. Although the boundary condition is a mathematical concept, intuitively, for example, why does a metal ball act as an electromagnetic shield? In fact, it can be explained that the metal ball provides a boundary condition for the electric field distribution in the space, thus changing the electric field distribution in the space. The example of a coaxial line can also be seen as an electromagnetic wave radiated from an intermediate wire, which is isolated by the outer shield (although this is not the case). The boundary conditions provided by the shield change the individual wires. Electric field distribution. (It's like you insert a stick in the water stream and the natural water flow changes) Electromagnetic waves have a feature of this thing, that is, the higher the frequency, the more easily attenuated, taking the base station as an example. 2G (GSM) is generally 800-900MHz. If you build a high tower, you can cover an area with a radius of 2-3km, and 4G (LTE) is generally 2.xGHz. If you build a tower in the middle of the playground, you will not see it. Can cover the entire playground. PS: If you are interested, you can take a look at the theory of the transmission line, which is extremely interesting and subverts your traditional perception of wires. ------------------------------------------------ Finally, answer these two questions directly, assuming that the wires in the title refer to metal wires: 1. Why can the wire trap electromagnetic waves? Wires cannot trap electromagnetic waves. The reason for this illusion is because: 1.0. No electromagnetic waves exist at the time of direct current; 1.1. At low frequencies, it is difficult to radiate wavelengths that are too long with respect to the length of the line. The main electric and magnetic fields are also distributed inside the conductors and are generally not considered as electromagnetic waves (except for ultra-long transmission lines); 1.2. Do not radiate at high frequencies early → _→ 2. The electromagnetic wave has energy. The electromagnetic wave does not need media. What is the role of the wire? 2.0. In the case of DC, it is necessary for the conductor to provide free electrons to establish the current. 2.1. In the case of low frequencies, it is generally equivalent to a lumped parameter circuit. Nobody regards it as an electromagnetic wave. The meaning of the wire is to pass the current... 2.2. Hello everyone, I am a boundary condition. This problem personally feels we need to start with the sources of electric and magnetic fields. There are two sources of electric field: 1 magnetic field with a change of charge 2 There are two sources of magnetic field: 1 Electric field with 2 changes in electric field 1. When conducting in a conductor, the conductor has a charge and a current. Then it has two sources of electric and magnetic fields, and they are guided by the conductor. 2. In the air, electromagnetic fields can only depend on each other and spread as the source of each other. The first method is conducive to dissemination and preferred. When there is time later quantitative analysis. ___________________________________________ Do a detailed explanation: 1. Two sources of electric field: 1 Charge: This is the basic concept in learning electricity. The electric field starts with a positive charge and ends with a negative charge. Gauss's theorem corresponding to Maxwell's law. Typical applications are electron accelerators in older picture tubes. 2 Changed magnetic field: This is Faraday's law of electromagnetic induction. The changing magnetic field produces a changing electric field that corresponds to Maxwell's law Faraday's law of electromagnetic induction. . The typical application is a generator. 2, two sources of magnetic field: 1 Current: This is what Auster discovered in April 1820 for the magnetic needle, the magnetic effect of current. The Ampere loop law that corresponds to Maxwell's law. The typical application is an electromagnet. 2 Changing Electric Fields: This is Maxwell's greatest contribution to the process of arranging Maxwell's equations. The concept of displacement currents has been introduced so that Ampere's Law of Circuits can be applied. typical application. . . (Not yet thought of, welcome to add.) First, when transmitting through a conductor (only transverse electromagnetic waves are considered here): The source of the electric field is the charge, the relationship between the charge and the electric field (where the electric field does not refer to the strength of the electric field and there is a voltage, there is an electric field): Voltage V = charge Q/(capacitance C) The source of the magnetic field is the current, magnetic field and current (again, where the magnetic field does not specifically refer to magnetic field strength): Magnetic flux φ = inductance L × current i Electric field energy = (1/2)CV^2 (2nd power of V, same below) Magnetic Field Energy = (1/2)Li^2 When propagating in a conductor, the electric field energy and the magnetic field energy are converted into each other. Therefore, there are: Electric field energy = magnetic field energy which is: (1/2)CV^2 = (1/2)Li^2 According to the above formula, we have obtained a very important conclusion: V/i = (L/C)^0.5 V/i is very familiar with right or wrong, this is the resistance in Ohm's law, in this unit is still ohm, but it is no longer the resistance, because transmitting in the ideal lead does not consume energy. Here is the characteristic impedance of the ideal transmission line. Second, when spread in a vacuum Electric field energy = (1/2) × dielectric constant × square of electric field strength = (1/2) * ε0 * E^2 Magnetic field energy = (1/2) × magnetic permeability × square of magnetic field strength = (1/2) *μ0*H^2 When it propagates in a vacuum, the electric field and the magnetic field transform into each other and the energy is equal, that is: Electric field energy = magnetic field energy (1/2)*μ0*H^2 = (1/2)*ε0*E^2 Then tidy up and get: E/H = (μ0/ε0)^0.5 We have another major discovery. This is the electromagnetic characteristic impedance in vacuum, which is about 377 ohms. Third, other stated problems Spreading through conductors and propagating in vacuum are two modes of electromagnetic waves. According to our needs to make a choice, you can also make a conversion: Transmitting through conductors into vacuum (or air) is the transmission antenna From the vacuum (or air) to the transmission through the conductor, is to receive the antenna It is only during normal use that most of us need to limit the energy of the electromagnetic field between the conductors (coaxial cable, microstrip line, strip line, etc.). If the design is not good, let the electromagnetic field energy leak out (transmit in vacuum). , electromagnetic compatibility problems arise. I think the real concern is that when we pass through a conductor, if we specifically design it, we can guarantee that most of the electromagnetic field energy is limited between two conductors (such as microstrip lines). why? One frequency domain expression borrowing Maxwell's equation is: ∇×H=J(current source)+jw*ε0*E(variable electric field source)=σE+jw*ε0*E H: magnetic field strength ∇×H: the curl of the magnetic field strength J: current density j: imaginary number, the square of j is equal to -1 w : angular frequency = 2Ï€f (f is frequency) Ε0: vacuum dielectric constant, ε0=8. 85 × 10^(-12)F/m E: electric field strength σ: conductivity Among them: J = σE is the microscopic form of Ohm's law In the case of a certain electric field strength E: When propagated in vacuum, the transformation from electric field strength to magnetic field strength follows (changing the electric field as a magnetic field source): ∇×H = jw*ε0*E When passing through a conductor, the transformation from electric field strength to magnetic field strength follows (current as a magnetic field source): ∇×H = σE We compare the size of σ and w*ε0 For copper (20 degrees): σ = 5.9×10^7 S/m 1KH electromagnetic wave: w*ε0 = 5.56×10^(-8) S/m 1MHz electromagnetic wave: w*ε0 = 5.56 × 10^(-5) S/m 1GHz electromagnetic wave: w*ε0 = 5.56 × 10^(-2) S/m The frequency of the light is 10^15. At this time, w*ε0 = 5.56 × 10^4 S/m. At this time, the conductor has already held the electromagnetic wave. At low frequencies, w*ε0 is much smaller than σ (N is a few orders of magnitude worse), so in the case of a given electric field, the conversion efficiency of the current as a magnetic field source is much greater than that of a changing electric field as a magnetic field source, so the conductor can confine the electromagnetic wave . (At low frequencies, current is too strong as a source of the magnetic field. Changing the electric field as the source of the magnetic field is too frustrating. It is not a number of players.) In fact, to be more intuitive, we can use two propagation modes, analogous to the parallel connection of two resistors. In the case of a certain voltage, we prefer to select the current with small resistance. people who use Zhihu Physics, mathematics | Didn't anyone notice the perfect symmetry of my name? Did you use a drainage stick when doing chemical experiments? And the thing that transmits electromagnetic waves is called the waveguide, not the wire, and the wire is the current. Their principle is completely different. Other answers also confuse the coaxial wires and waveguides. End of the Moon Picking the wrong professional engineering dog: Can comrades not answer well? The so-called wire is a boundary with free electrons. When the electromagnetic field encounters this boundary, it interacts with the electrons in the wire to form a scattered field. After superimposition with the original electromagnetic field, a specific electromagnetic field distribution will be formed to achieve the purpose of transmitting electromagnetic energy. The same is true for the waveguide, and there is no difference between the antennas. I changed it according to the comments. The waveguides and antennas mentioned above are also the same, meaning that these structures are all boundary conditions. There is no difference in nature except that the field distribution is different. Patrick Zhang: There are two questions for the subject: 1) Why can the wire trap electromagnetic waves? 2) The electromagnetic wave has energy. The electromagnetic wave does not need the medium. What is the role of the wire? These two issues are very insightful and are the root cause of why the wires conduct electricity. Let's look at three additional issues: 1) Is the wire passing electrical energy, electric field or electron? 2) The movement speed of the electrons in the wire is only about 1 cm/sec. How is the power transmitted to the load? 3) Why is it not recommended to use water as a metaphor for electrical phenomena? These issues are the favorite of middle school students. Let us discuss some of them for the time being. Po Yinting, people do not pay much attention to his theory. The reason is that his theory is based on Maxwell's electromagnetic theory and it feels a bit tall. However, the application of Poynting's theory is extremely wide, but we do not know it. We know that electromagnetic waves are a physical form that exists objectively. It has a certain amount of energy. In order to illustrate the energy transfer situation, the concept of the energy flow density S is defined: The energy flow density S is equal to the energy per unit time passing through a unit area perpendicular to the energy propagation direction. The direction of S points in the direction of wave propagation. The energy flow S vector is the Poynting vector. In the plane wave: Note that the multiplication sign here refers to the cross product of vectors, ie: We look at Figure 1: The wire radius in Figure 1 is r and its length is L. Current I flows through the wire, and the conductivity of the wire is γ. Inside the wire, the electric field strength is: In the electric field strength expression, the first fractional numerator is the current density J, and the second fractional numerator is the current I, so the wire cross-sectional area appears in the second fractional denominator. Inside the wire, the magnetic field strength is: Now that we consider the surface of the wire as the closed surface, the power absorbed by the wire is: Here R0 is the resistance of this section of wire. We see that the conclusion here is consistent with what we are familiar with in the middle school. From this we can see an important fact: the power provided by the power source is used as part of the loss of the wire, and the other part is transmitted to the load at the end of the wire. What about the energy distribution inside and outside the wire? We use the Poynting vector to calculate the result. First look at the Poynting vector form: We divide the wire into two parts: the inside and the outside. The radii of the two parts are R1 and R2 respectively. Then we do the following integration: What does this mean? First: No electronics are involved in the calculation. It can be seen that the main body of the transmission energy of the wire is not the electron but the electric field. Second: Electromagnetic energy is transmitted through the surface of the conductor and the surrounding medium. The conductor plays a guiding and guiding role. Third: The energy passed by any section of the wire is equal. These three articles have in fact answered the question of the title. Look at the side problem again: 1) Is the wire passing electrical energy, electric field or electron? Answer: The transmission of electrical energy by the wires depends on the electric field, not the electrons. 2) The movement speed of the electrons in the wire is only about 1 cm/sec. How is the power transmitted to the load? Answer: As above, combined with the previous deduction, electric energy is transmitted to the load by electric field. 3) Why is it not recommended to use water as a metaphor for electrical phenomena? Reply: Middle school students particularly like to use water to compare electrical phenomena. Through the above explanation, we found that the transmission of electricity is completely different from that of water, and there is no hair relationship between the two. It can be seen that the analogy of electrical phenomena with water is very inappropriate. I remember that when I went to "Ordinary Physics" (we didn't call college physics at the time, it was called general physics), the teacher also talked about the transmission of electricity when Poyntin vector was explained. After the class, everyone had a discussion. The discussion questions are as follows: For a power distribution system, from the transformer to the numerous end users, there are many cables and wires in the middle. The transmission of electric energy is of course carried out through these cables and wires. If there is a short circuit between the phase line and the ground line at some point, leakage occurs. How is this leakage explained by Poynting electric transmission theory? The main points discussed at the time were: First, the leakage point is not necessarily a wire, it may be a wet underground soil, then an underground steel mesh, and other conductive materials. What is the relationship between these materials and the Poyntin vector? How do they bind electromagnetic waves? Second: The effect of resistance can be seen faintly from the Poynting vector and implies that we can get Ohm's law (Ohm's theorem) from Maxwell's theory. Then, what is the resistance of the leakage current through the Poynting electric energy transmission theory? These two questions are given back to our friends for your thoughts. When necessary, I will answer. Seeing the commentary area made many observations about the analogy of electricity with water. I talk about my personal understanding: I remember that in the middle school era, teachers did use water to analogize electricity. However, after entering the university classroom, this analogy has almost disappeared. After entering the workplace, the use of water as a metaphor for electric phenomena can no longer be heard. Because the electricity phenomenon has its own laws, this law cannot be described by water at all. Now, I have a part of my task is to teach. When explaining Maxwell's electromagnetic force, I would ask the students: Do you still use water to analogize electromagnetic phenomena? Everyone said in unison that they would not, because the two are too far apart. Instead, the study of magnetic flux will draw analogy of current, but there are Kirchhoff's first and second laws, and Ohm's law of the magnetic circuit, and so on. I have read German high school physics textbooks. In these textbooks, there is absolutely no text that uses water as a metaphor for electricity. However, other countries can hardly say it. One time in ABB and a bearded man from India to discuss the principle of self-control, he still used water to describe the phenomenon of electricity, I deliberately led him to explore in depth, after a few words his water theory can not continue. So he also admitted that using water to compare electrical phenomena is not very appropriate. My approach is: Willingness to use water to compare electrical phenomena, just like replacing the three-phase neutral line with the concept of zero line. Although it is inappropriate, it cannot be corrected. So, if you are willing to use it, use it as long as I don't use it myself. Ah Q is not it? laugh! Kang Rang: The transmission of electromagnetic waves does not require a medium, but it does not mean that the electromagnetic waves do not need media to produce them. The time-varying currents on each wire of the two conductors individually generate a time-varying electromagnetic field, which is then superimposed with the time-varying electromagnetic field generated by the other wire: the field strength is superposed positively between the two wires, and the field strength is reversed outside the two wires. offset. So the electromagnetic wave travels mainly along the two wires and looks like it is bound. In fact, the so-called word of restraint is only a generalized understanding of mathematical language. In other words, we use the word “tethering†to easily understand a lot of complicated mathematical formulas. The word electromagnetic wave is also a popular understanding of mathematical language. There is no electromagnetic wave in the world. Who has seen it? It is merely a popular expression of pure theory. It is only a comprehension of the hard mathematical relationship. It is just that the knowledge is transmitted to the electromagnetic wave as if it were to become an independent, objective fact like a water wave. The purpose of establishing scientific theories is to better fit and understand the world. And any theory, only through natural language can we get a real final understanding. Therefore, we only need natural language such as conduction, restraint, and electromagnetic waves to understand theories, and indirectly understand the world. There is a saying that is good: People sometimes go too far and forget why. . . LoserWu: simply put. . Most of the electromagnetic fields in the circuit do not have the conditions for propagation in space. (Forgive me directly from the Baidu Encyclopedia to find maps) can be seen, the electromagnetic field to spread, the electric field of the magnetic field must be infinitely time-directed. (Specifically spread in space, at this time there is no current density j. However, most of the circuit is a DC circuit, this time the current size direction does not change. Then please allow me to come up with the physics version of Ohm's law j = γE (do not care Details, in short, directly think that the current is proportional to the strength of the electric field, in fact, the high school version of Ohm's law can also be introduced?) Then find the electric field is constant, naturally no way to spread. So what is the electric field in the circuit in the end? ? Referring to this picture, the resistance is not considered first. Let's think about how the electric field is set up by connecting the leads on both sides of the battery. First, the positive and negative levels of the power supply have a large number of positive and negative charges, respectively, and then an electric field is generated in space. Probably like this It can be found that at this time the electrons in the wire, the electric field is all in one direction. . Then we look at the right bend place. Both the upper and lower electrons are far away from the rightbend, apparently leaving a static charge at the right bend. Then the electrons in each part of the wire are redistributed in a similar manner and eventually reach an equilibrium state. When can we balance it? To achieve the same current everywhere, that is (if you do not consider resistance) electric field only along the wire, and everywhere the same. If it is not the same or not along the wire, there will be static charge accumulation, and the current and output current of this node will be different. After balancing, it becomes like this. At this time, there is only a net charge on the surface of the wire. . Then the electric field is perpendicular to the surface of the wire, and the electric field inside the wire is zero (if the wire is considered to have no resistance.) Let's look at the previous figure again: Where there is a resistance, because the current is the same as elsewhere (otherwise there will be charge accumulation at the node and it cannot be balanced). The electrical conductivity γ of the resistor is a finite value, so there is an electric field in the resistor that is parallel to the wire. . Of course, at this time, the electric field on the surface of the resistor will not be perpendicular to the surface, but there will be a tangential component. Now to answer the question, energy is indeed transmitted through electromagnetic waves. why? If the energy is directly transmitted by the kinetic energy of the electrons, the electron speed before and after the resistance will change. However, as we said before, the current in the circuit must be the same, and the current reflects the speed of the electron (I=nAvQ), so the electron speed does not change before and after the resistance. The correct process of energy transfer is that the electromagnetic field around the wire transports the energy to the vicinity of the resistor, creating an electric field along the wire inside the resistor. This electric field accelerates the electron and the electron acquires kinetic energy and transmits it to the resistor. Before and after the electronic kinetic energy is unchanged, it is only a medium that transmits energy as an electromagnetic field. At this time, what is the role of the wire? The electromagnetic field at this time does not have the space propagation condition, so the electromagnetic field wants to propagate, must make the current density j in Maxwell's equations not zero. There is current in the wire, and the electromagnetic field can rely on the current transmission. By the way, in fact, for some special circuits, it is possible to create a spatially propagated electromagnetic field. Such as LC oscillation circuit. Why can the wire bind the electromagnetic wave? The wire is electronically bound. Because the electrons escaping require very high energy, the voltage of the wires is not usually high enough. If the voltage is high enough, electrons will be emitted (think of the photoelectric effect, which is actually an auxiliary emission). Electromagnetic waves have energy. Electromagnetic waves do not need media. What is the role of the wire? The role of the wire is to bind the electrons. ************************************************** *********** The energy transmitted by the wire depends on the electromagnetic field, but it is not the electromagnetic field or electron that is transmitted. It is only driven by the repulsion of the electromagnetic field between the electrons. Statistically speaking, we can see the net flow of electrons in a certain direction. Water pipes also rely on electromagnetic fields to transmit energy, but instead of electromagnetic fields, water molecules are transported by the electromagnetic field repulsion between water molecules. Statistically speaking, they see the net flow of water molecules in a certain direction. So I think Teacher Zhang's answer is incorrect. Junior of HNU: Wang Yang According to Feynman, the electromagnetic wave tried all the paths and found that the “effect path integral†along the wire was the smallest, and this path was chosen. Xie Yankee RF Engineers Focus on Base Station Amplifiers and DPD Whether it is a DC transmission line or a microwave transmission structure, they can be collectively referred to as waveguides. As the name implies, it is guided by electromagnetic waves. To clarify a concept, that is, regardless of the frequency, electromagnetic energy is transmitted in the medium in the waveguide, this medium can be air, other materials or vacuum. Therefore, the electromagnetic energy in the DC circuit also propagates in the medium between the wire and the reference plane. Shengeleven Add my opinion. Almost any electromagnetic problem can be attributed to solving Maxwell's equations under given conditions. Therefore, the role of the wire is to provide boundary conditions for Maxwell's equations, that is, to provide an application scenario for this set of equations. Above (taken from Wikipedia): In the figure, red is the electric field, green is the magnetic field, and blue is the Poynting vector, which is the direction of energy flow. Power: Poynting vectors outward, so the energy travels outward, not along the current direction. Wire: The wire connecting the two ends of the power source has a potential difference, and the energy of ExH is transmitted between the two wires. So the wire is equivalent to a waveguide. Resistance: Inward energy flow occurs around the surface, and energy is absorbed by the resistor to generate heat. to sum up, 1. Electromagnetic energy is not propagated through the wire, but is propagated through the electromagnetic field in the space around the circuit; the wire provides the boundary conditions of Maxwell's equations, and the wire acts as a waveguide. 2. The Poynting Theorem is not applicable to dynamic electromagnetic fields. Static fields are also applicable. It feels clearer than what I said. Mu Xia: Hey, magic, not called the waveguide, do you mean that the optical name has not changed in half a year. Why the waveguide can bind light because of total reflection. Why use a waveguide, because it is impossible to launch a completely parallel beam, if not constrained, it will not be dispersed for a while. And it doesn't turn around without giving restraint, and it spreads the signal. snake melon The conductor only plays the role of the conductor in the transmission of electromagnetic energy. The electromagnetic energy that travels along the conductor is actually flowing through the space around the conductor rather than flowing inside the conductor to the load. The energy flow forward of the conductor is concentrated in a limited cross section near the wire. Excerpts from 44 pages of electromagnetic field and electromagnetic wave teaching materials (edited by Lei Hongyu and Liu Liguo) Yang Yang Wires that can bind electromagnetic waves are generally called optical fibers. You haven't figured out the difference between electric fields and electromagnetic waves. If you want to say an electric field, the speed of the current is not the speed of the electrons in the wire, but the electric field. The speed of transmission is also not binding. Sheng Xun Why can the wire bind the electromagnetic wave? wrong. Wires cannot bind electromagnetic waves. The electromagnetic wave has energy. The electromagnetic wave does not need media. What is the role of the wire? First, wires can increase transmission efficiency! The cable TV effect is better than the antenna. This is evidence. Second, the wires can conduct direct current! David De 2015 Teacher Zhang is very professional, but personally feels less intuitive. I think there is no problem understanding the electromagnetic field with water. As we all know, electromagnetic waves are the performance of electromagnetic fields in space propagation, and they are essentially waves. This is the same as the propagation of water waves caused by throwing stones at the pond. Waves propagate in space, but water molecules only make vibrations up and down. In the same way, the electromagnetic field in the wire is propagated at the speed of light. The electrons caused by it do not propagate with the electromagnetic field at the speed of light, but move at a low speed, resulting in losses. The problem with the subject is that the electromagnetic field does not require the propagation of the medium, but the movement of the electron requires the medium. If there is no wire, and only the vacuum is used as the propagation path, the electrons cannot move. Therefore, the role of the wire is to provide a path for electrons to move with the electromagnetic field. Intuitively, it can be understood from the pond wave, although it is different but it helps to understand. people who use Zhihu No media is a means of transmission Wires with different cross-sectional shapes are also the means of transmission Even insulators (such as fiber optics) are a form of transmission Just like you can walk, you can still use different modes of transportation. And most of the time you will tend to use more energy-efficient transportation. The situation of the wire is like you are thrown on a highway, not allowed to walk, can only leave by car (wire), but the car has a different model (different wire mode). Sudden braking, acceleration, turning or uneven roads can throw you out of the car. Become radiation. Rylc: I was shocked to see so many answers given by many professionals. If the subject is talking about the fiber, then it is because of the principle of total reflection that it can be transmitted all the time without losing energy. If ordinary cables are mentioned, then electric fields are generated between the power sources, but only the electrons in the wires can be free and automatic in the electric field (not because of the electromagnetic field), so electric currents are generated. The surrounding air insulation is very high, it is difficult to have free electrons, so there is no current. The essence of the current is the directional movement of the electrons, not the electromagnetic field, and more not the electromagnetic wave, although it can generate electromagnetic fields. The electric field generates a magnetic field, and the magnetic field also generates an electric field, so it is called an electromagnetic field. A changing electric field causes a changing magnetic field, and a changing magnetic field can generate a changing electric field, and so on. If the change is appropriate (such as a sinusoidal change), then electromagnetic waves can propagate continuously. However, this has nothing to do with the things in the wire. Electromagnetic fields, electromagnetic waves, one is a field, and one is a wave, and changes in the field will produce waves. Cao Yuyuan Because the electromagnetic wave will rapidly decay into the metal, there is no way to penetrate the metal. Of course, the conductor can be like water and soil, and there are many kinds of attenuation of the electromagnetic wave. It does not have to be metal. The wire, as its name suggests, is to guide the propagation of electromagnetic waves, such as waveguides and coaxial lines, and you can understand the distribution of internal fields. Small plug male engineer The role of the transmission line is to act as a boundary condition, so that the electromagnetic wave forms a series of (stationary) modes along the cross section of the transmission line. There are fundamental modes and high order modes. Of course, the energy is concentrated in the fundamental mode. It has spread along the transmission line LX2017 Who says that wires can bind electromagnetic waves? Is this crap? Electromagnetic wave leakage occurs when current is conducted in the wire. The higher the frequency of transmission, the more severe the leakage. Electromagnetic waves can be transmitted in a vacuum, but wires are essential. Because it provides a low resistance path for electromagnetic waves.电ç£æ³¢é¢‘率越低这个通é“就越é‡è¦ã€‚ Solid-state Capacitors / Motor Starting Capacitors
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