What Is Electromagnetic Theory?

Since people discovered electrical phenomena, magnetic phenomena, and electromagnetic induction phenomena, they have conducted in-depth and extensive research on electrical, magnetic, and electromagnetic induction phenomena, discovered the relationship between electromagnetics and their laws, and formed a complete and systematic electromagnetic theory. Electromagnetic theory has promoted the development of science and technology and has strongly promoted the progress of society. Electromagnetic theory holds that a changing electric field is accompanied by a changing magnetic field, and a changing magnetic field is also accompanied by a changing electric field.

Electromagnetic theory

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

Maxwell's equations are composed of four differential equations:

(1) · E = / _0, describing the nature of the electric field. In general, the electric field can be a Coulomb electric field or an induced electric field excited by a changing magnetic field, and the induced electric field is a vortex field. Its electric displacement line is closed and does not contribute to the flux of the closed surface.

(2) · B = 0, describing the nature of the magnetic field. Magnetic fields can be excited by conduction currents or by displacement currents with varying electric fields. Their magnetic fields are all vortex fields, and their magnetic induction lines are closed lines, which do not contribute to the flux of the closed surface.

(3) × E = -B / t, which describes the law of the electric field excited by the changing magnetic field.

(4) × B = ₀ J + 1 / c ² * E / t (c ² = 1 / _{0 0} ), which describes the law of the changing electric field excitation magnetic field.

Maxwell's equations are all expressed using calculus. The equations involved include:

1. Gauss's theorem, the electric displacement flux through any closed surface is equal to the total amount of charge inside the closed surface. Maxwell: The divergence of the electrical displacement is equal to the charge density.

2. The magnetic flux continuity theorem, that is, the magnetic lines of force are always closed, and the magnetic field has no scalar source. Maxwell's formulation is: find the divergence of the magnetic induction intensity to zero.

3. Faraday's law of electromagnetic induction, that is, the electromagnetic fields are transformed into each other, and the rotation of the electric field strength is equal to the negative partial derivative of the magnetic induction strength with respect to time.

4. The Ampere Loop Theorem is that the loop strength of the magnetic field along any loop is equal to the algebraic sum of the currents enclosed by the loop.