Time-changing electromagnetic field

Time-change electromagnetic field is an electromagnetic field that varies over time. There is a significant difference between the current electromagnetic field and the static electric field and the magnetic field, and some effects generated due to time changes. These effects have important applications and promote the development of electrician technology.

If the two pass into the parallel wire of the same-to-direction current, the wire right is bent to the right, and the planar coil is the simplest magnet, then according to the interaction of the parallel current. The conclusion of the extension force is generated. At this time, the power-on-plane coil on the right is generated between the winding wires on the left.

Similarly, if the right-to-right power conductor is curved into a planar coil, the coil is repulsive between the winding wire on the left, if the right power coil can rotate around the central axis, right The fluid coil will generate the flipping motion of the axis under the action of the repulsive force, and until it is flipped to the position where the maximum gravitational force can be generated with the energization wire on the left, at this time, the current direction of the left curved coil will be turned over. The motion of the movement will consistent with the current direction of the right curved coil, and no longer generate the flipping movement of the axis.

According to this, if all the wires around this fluid wire bend into a fluid coil, the power-of-electric coil can be generated with the center of this power supply wire, which will be circulated under the role of repulsiveness. The flipping movement of the axis.

If these power coils are placed around the power-on wire, at the small magnetic needle on the same plane, at which time all small magnetic needles around the wire wire will form a circle NS around the power transfer wire. The circular distribution of small magnetic needles connected to the extremely tail. This is the reason why the small magnetic needle around the fluid wire can generate a rotation of the axis, and can form a small magnetic needle circle distribution of the NS diode around the energized wire.


m. Farase proposed electromagnetic induction law indicates that the change in the magnetic field should generate an electric field. This electric field is different from the electric field derived from Corlomb's law. It can drive current flow in the closed conductor circuit, that is, its loop points may not be zero, becoming an inductive electromotive force. Modern large applications of power equipment and generators, transformers, etc. have a close relationship with electromagnetic induction. Due to this role. The vortex and skin effect will be generated in the bulk conductor in the event. In the electrical industry, the sensing heating, surface quenching, electromagnetic shielding, etc. are the direct application of these phenomena.

After the finalization of the electromagnetic induction law, J.c. Maxwell proposed a displacement current concept. The electrode movement is derived from the electrical particles in the dielectric to the electric field force in the electric field. Although these charged particles cannot flow freely, the tiny displacement at an atomic scale occurs. Maxwell generally promotes this noun to the electric field in the vacuum; the potential shift is also generated by the magnetic field, so that the time change rate of the electric flux is called a displacement current, and the time derivative of the electrode shift vector D (ie дD / дT) is a displacement current density. In the law of ampere loop, in addition to the conductive current, it has completed the function of the displacement current, thereby summarizing the complete electromagnetic equation group, that is, the famous Maxwell equation, describes the distribution of electromagnetic fields.

The field of electric field is accompanied by a magnetic field while changing with time, and the field of magnetic field is accompanied by electric fields when changing over time. The electric field and the magnetic field are interdependent, mutual causal, and form a unified electromagnetic field. The electrostatic field or a static magnetic field can be independent, which is an important difference between static field and time-bearing field. Once the electric field or magnetic field at a certain change, the wave is propagated in the form of the wave to form an electromagnetic wave. The basic equation of the time-variable electromagnetic field is the Maxwell equation group and the constituent equation.

, like substances in nature, the electromagnetic field has energy, momentum and quality, which is a special form of substances.

Energy in electromagnetic field

Linear medium energy density WE and magnetic field energy density W M is

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typically D is the electrical displacement vector; E is the electric field strength; b is the magnetic induction strength; H is the magnetic field strength. In the time-shifting electromagnetic field, they all change over time, according to the energy conservation principle, natural accompanying the flow of energy.

Slope Release Vector

is represented by s, S = E × H, the area of ​​the closed face A is divided into the closed surface A

represents the closure within the unit time Energy spread outward in the face A, that is, energy flow. The vectors of the slope represents the energy of the unit area in the unit area, which can flow density. It is often used in radio engineering to analyze the radiant energy of the antenna or radiation power.

Momentity of electromagnetic field

In linear isotropic medium, the electromagodyne or electromagum amount of electromagnetic amount G is

Case and Application

When the electromagnetic field is excited by a single frequency as a sinusoidal change, according to the sinusoidal change.

Electromagnetic radiation

Maxwell equation shows that not only changes in the magnetic field to generate electric fields, and the change in electric fields also generates a magnetic field. At this interaction, electromagnetic radiation is generated in this interaction, that is, electromagnetic waves. This electromagnetic wave is propagated from the field source to the surrounding, and in the space in which the space is far from the far source, there is a corresponding time hysteresis. There is an important feature of electromagnetic waves that there is a relatively similar component in the field vectors to the distance between the field to the observation point. These components are attenuated at the time of space propagation. According to the slope, the electromagnetic wave is in propagating energy, which can be used as a carrier of information. This has broadening the road for radio communication, broadcast, television, remote sensing.

Similar to stable electromagnetic field

Different from the above phenomenon of static field, the significance is closely related to the frequency of the frequency and the size of the device. According to actual needs, in the allowable approximation, the partial process of time change can be treated as a constant field, referred to as a stable electromagnetic field or quasi-static field. This method makes analysis work greatly, and it has been widely adopted for people in electrical technology.

The alternating electromagnetic field when the alternating electromagnetic field and the transient electromagnetic field may further be divided into a transient electromagnetic field for a cycle change electromagnetic field and a non-periodic change. There are some features of their own research on their research and methods.

The alternating electromagnetic field can be used under the sinusoidal variation of a single frequency, and there is a lot of application in power technology and continuous wave analysis. The transient electromagnetic field is also known as pulse electromagnetic fields, and the frequency of coverage is wide, and the medium or transmission system exhibits dispersion characteristics, often requires a frequency domain, or timing deployment, and the like.

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