Maxwell s theory of electromagnetism does not say that a non uniformly varying electric field produc

Pay attention to the difference between electrostatic and constant electric fields.

Electrostatic fields (e.g., single or multiple stable charged bodies) do not produce magnetic fields.

The constant electric field is formed by the joint excitation of the charge on the two poles of the power supply and the charge accumulated on the conductor or other electrical elements, and its characteristic is that the electric field lines are everywhere along the direction of the conductor, which is similar to the electrostatic field, but there are also differences, the difference is that it has an additional conduction current.

Maxwell's equations have an equation that is.

j is the conduction current density, d is the electric displacement vector, e is the electric field strength, and the following relationship exists in isotropic media).

For the electrostatic field the first term does not exist, while a constant electric field exists,; For the second term, neither exists, so the result is that there is a constant magnetic field for a constant electric field and no magnetic field for an electrostatic field.

When the power is just turned on, the current in the circuit is from nothing, and when the switch is disconnected, the current is from there to nothing, so DC can also produce a changing magnetic field, understand?

Doesn't direct current produce a changing magnetic field, unless the system that generates the magnetic field is moving regularly?

Remember: a magnetic field can be generated by direct current, a constant magnetic field in a constant power plant, and a changing electric field in a variable magnetic field. As long as the energized solenoid is energized, it will produce magnetism, which can be used as a magnet, and the closure of the switch on the energized solenoid is used to control the presence or absence of the magnetic field of the solenoid, which is the changing magnetic field!

If you still have questions, send them back!!

—Mr. Lin.

An electric current or a changing electric field produces a magnetic field.

There is an electric current in the energized wire The current is constant, producing a constant magnetic field.

Maxwell's two major hypotheses about electromagnetic field theory are the hypothesis of "induced electric field" and "displacement current".

1. Induced electric field.

The effect of the induced electric field on the free charge is only an equivalent conjecture, so the vortex electric field is a virtual electric field. This eddy electric field is not present around the changing magnetic field and is attached to the changing magnetic field.

2. Displacement current.

The displacement current is the integral of the rate of change of the electrical displacement vector over time to the surface. However, the displacement current only indicates the rate of change of the electric field, and unlike the conduction current, it does not produce thermal effects, chemical effects, etc.

Extended Information: After 1861 he worked in electromagnetism.

In the same year he published "On the Lines of Force in Physics", designed a mechanical model of electromagnetic action, and introduced the concept of displacement current.

In 1864, he read the "Kinetic Theory of Electromagnetic Fields" at the Royal Society, which further summarized the theory of electromagnetic fields and proposed the basic differential equations of electromagnetic fields, that is, the famous Maxwell's equations.

He foresaw electromagnetic waves on the basis of his study of electromagnetic fields.

exists, in Huygens.

On the basis of Gram's wave theory, he put forward the electromagnetic theory of light, which believes that light is an electromagnetic wave with a certain frequency range, and the measured speed of electromagnetic waves is very close to the speed of light. The electromagnetism of light is a leap forward in human understanding of the nature of light.

Vortex current assumptions.

Displacement current assumptions.

The core idea of Maxwell's electromagnetic field theory is that a changing magnetic field can excite a vortex electric field, and a changing electric field can excite a vortex magnetic field; The electric field and the magnetic field are not isolated from each other, they are interconnected and excite each other to form a unified electromagnetic field. Maxwell further synthesized all the laws of electric and magnetic fields to establish a complete theoretical system of electromagnetic fields.

At the heart of this system of electromagnetic field theory is Maxwell's equations.

Maxwell's equations are made up of four differential equations, :

1) The properties of the electric field are described. In general, the electric field can be either a Coulomb electric field or an induced electric field excited by a varying magnetic field, while the induced electric field is a vortex field whose electrical displacement lines are closed and do not contribute to the flux of the closed surface.

2) describes the properties of the magnetic field. The magnetic field can be excited by a conduction current or a displacement current that changes the electric field, their magnetic fields are eddy fields, and the magnetic induction lines are closed lines that do not contribute to the flux of the closed surface.

3) The law of the excitation of the electric field by a changing magnetic field is described.

4) The law of excitation of the magnetic field by a changing electric field is described.

Maxwell's equations are expressed in calculus, and calculus is used for specific derivation, and it is difficult to understand if you don't study high school, I will write out the equations involved for you, and make an explanation, if you don't understand it, don't worry, and you can understand calculus when you go to college:

1.Ampere's loop theorem, which states that the amount of the magnetic field strength along any loop is equal to the algebraic sum of the currents enclosed by the loop.

2.Faraday's law of electromagnetic induction, that is, electromagnetic fields convert each other, and the chorus of the electric field strength is equal to the negative bias of the magnetic induction intensity to time.

3.The magnetic flux continuity theorem, that is, the magnetic field lines are always closed, and the magnetic field has no scalar source, Maxwell stated that the divergence of the magnetic induction intensity is zero.

4.According to Gauss's theorem, the flux of electrical displacement through an arbitrary closed surface is equal to the total amount of charge inside that closed surface. Maxwell: The divergence of the electrical displacement is equal to the charge density.

ps: I majored in physics, just ask me if you have questions about physics, Maxwell's equations are the essence and soul of the electromagnetic field part, not a sentence or two can be made clear, I can only explain these.

by Maxwell.

Theory of electromagnetic fields.

It can be seen that a changing magnetic field must be generated around a changing electric field - wrong;

From Maxwell's theory of electromagnetic fields, it is clear that a magnetic field must be generated around a changing electric field – correct.

Not necessarily, the changing magnetic field can be around a constant electric field, provided that the rate of change of the magnetic field does not change.

He predicted the existence of electromagnetic waves. This theoretical foresight was later fully experimentally verified. He erected a monument to physics.

Radio technology, which benefits mankind, was developed on the basis of the theory of electromagnetic fields. Maxwell began to study electromagnetism around 1855, and after studying Faraday's new theories and ideas on electromagnetism, he was convinced that Faraday's new theory contained truth. Therefore, he had the desire to "provide a mathematical basis for Faraday's theory" and was determined to express Faraday's genius in a clear and accurate mathematical form.

On the basis of the achievements of his predecessors, he made a systematic and comprehensive study of the entire electromagnetic phenomenon, and with his profound mathematical attainments and rich imagination, he successively published three articles on the theory of electromagnetic fields**: "On Faraday's Line of Force" (December 1855-February 1856); On the Lines of Force in Physics (1861-1862);

Kinetic Theory of the Electromagnetic Field (December 8, 1864). The work of his predecessors and himself was comprehensively summarized, and the electromagnetic field theory was expressed in a concise, symmetrical and perfect mathematical form, which was sorted out and rewritten by later generations and became the main basis of classical electrodynamics. Based on this, in 1865 he predicted the existence of electromagnetic waves, which could only be transverse waves, and deduced that the propagation speed of electromagnetic waves was equal to the speed of light, while concluding:

Light is a form of electromagnetic wave that reveals the connection between light phenomena and electromagnetic phenomena. In 1888, the German physicist Hertz experimentally verified the existence of electromagnetic waves.

Your understanding is correct.

A uniformly varying electric field is generated around a constant current, and a uniformly varying electric field produces a constant magnetic field; A uniformly varying magnetic field produces a constant electric field.

Electromagnetic waves cannot be generated around a uniformly varying magnetic field and a uniformly varying electric field.

Electromagnetic waves can only be generated around a periodically changing magnetic field and a periodically changing electric field.

Judging by Lenz's law, according to the direction of the electric field (equivalent to the direction of the induced current), the direction of the induced magnetic field is judged to be downward, which is opposite to the direction of the original magnetic field, and the magnetic field in the upward direction is being strengthened by Lenz's law, and a is selected

e=-(b*ds) dt, as can be seen from the figure, can produce an electric field in the direction of the figure, and the direction of the changing magnetic field is opposite to the direction of the original magnetic field b. From this formula, it can be seen (there is a negative sign in front), so the original magnetic field b must be strengthened, and the direction is upward. Therefore, choose A, the magnetic field cannot change in the opposite direction, otherwise, the direction of E will change.

Therefore, CD is excluded.

Answer: A or C

Analysis: The electric field is an induced electric field, which can be judged according to Lenz's law.

Maxwell proposed that a changing electric field is equivalent to an electric current, which also produces a magnetic field, and this current is called (displacement current).The electromagnetic field has (periodic obligate genus).

1. Induced electric field hypothesis: The changing magnetic field produces an electric field, which is called the induced electric field.

2. Displacement current hypothesis: The changing electric field can be regarded as a kind of electric current, which is called displacement current, which excites the magnetic field. So it can also be thought that it is the changing magnetic field that produces the electric field.

Analysis] From Maxwell's electromagnetic field theory, it can be seen that with a balance, a changing electric field can produce a magnetic field, and a uniformly changing electric field has a constant chain of change to produce a constant magnetic field, and option A is correct and option B is wrong. An oscillating electric field is capable of generating an oscillating magnetic field; The oscillating magnetic field can produce an oscillating electric field, and options c and d are correct. To sum up, the answer is B.

Comments] This question tests the understanding of Maxwell's electromagnetic field theory, the meaning of Maxwell's electromagnetic field theory is that a changing electric field can produce a magnetic field, and a changing magnetic field can produce an electric field, and the nature of the generated field is determined by the rate of change of the original field, which can be determined by the tangent slope of the original field over time.