[b]The discovery of electromagnetic waves[/b]
Due to historical reasons (the first, the magnetic and electric independence was considered to be unrelated phenomena), but also because their development and magnetic applications, such as modern magnetic materials and magnetic technologies, new magnetic effects and magnetic phenomena discovery and application, etc., making the content of expanding magnetic, and magnetism in practice and also as a parallel to the electrical discipline to study. Electromagnetism from the original two mutually independent science (electrical, magnetic) to become a full branch of physics subjects, is mainly based on two important experimental findings that the flow of electricity generated magnetic effect, and changes in the magnetic field the resulting electric effect. These two experimental results, coupled with changes in JC Maxwell electric magnetic field on the assumption that laid the whole theory of electromagnetic system, the development of a significant impact on modern civilization from the electrical and electronic technology.
Maxwell's electromagnetic theory, the significance lies not only in the macroscopic theory of electromagnetic phenomena dominate everything (including static, stable magnetic field, electromagnetic induction, circuits, electromagnetic waves, etc.), but is it unified in the theory of optical phenomena within the framework of a profound impact on people's understanding of the material world of ideas. Electronic discovery, the electromagnetism and the theory of atomic structure and material are combined, HA Lorentz's electron theory of the macroscopic electromagnetic properties of the material attributed to the effects of atomic electrons, unified explanation of electric, magnetic, optical phenomena.
And electromagnetism is closely related to classical electrodynamics, both in content and there is no difference in principle. In general, electromagnetic emphasis on experimental studies of electromagnetic phenomena from a wide range of electromagnetic phenomena in the study summarized the basic laws of electromagnetism; classical electrodynamics the emphasis on theory, it Maxwell's equations and the Lorentz force based to study the electromagnetic field distribution, electromagnetic excitation, radiation and propagation and interaction of charged particles and electromagnetic fields and other electromagnetic problems, it can be said, contains a broad electromagnetics classic electrodynamics. Theory of relativity and quantum effects on the development of electromagnetism, see the electrodynamics theory of relativity, quantum electrodynamics.
Maxwell "Electromagnetic Theory" was published, because the theory difficult to understand, no experimental verification, for a long period of time has not been valued and widely recognized. In 1879, the Berlin Academy of Sciences set up a prize essay, required to prove the following three assumptions: ? If the displacement current exists, it will definitely produce a magnetic effect; ? changes in magnetic media will make the insulation displacement currents; ? in air or vacuum, The same is true of these two hypotheses. Hertz for the essay as a leader in electromagnetic experiments.
1885 Hz using a primary and two secondary windings of the coil oscillation experiment, accidentally discovered: When inputting one pulse on the primary coil current, the secondary winding ends of the slit will spark the middle,, Hz immediately think of This may be an electric magnetic resonance phenomenon. Since the primary coil of the oscillating current to provoke secondary spark, then it can produce oscillations in the adjacent medium displacement current, the displacement current in turn affect the occurrence of the secondary winding of the spark changes in the strength.
1886, Hertz has designed a linear open space of the ring oscillator is left as a sensor wire C, on a straight line near the oscillator AB, AB When the pulse current input and when the spark gap, the gap in C also produced sparks. This is the actual generation of electromagnetic waves, transmission and reception.
Prove the consistency of electromagnetic waves and light waves: March 1888 Hz the speed of electromagnetic waves were measured, and in the paper "On the air waves and their reflection," describes the determination of: Hertz measured the electromagnetic standing wave formed by the adjacent the distance between two wave section (half wavelength), and then calculated the frequency of the vibrator with the speed of electromagnetic waves. He in a large room wall nail a piece of lead sheet, used to reflect electromagnetic waves to form standing waves. A distance of 13 meters where a tributary of the vibrator as a wave source. With an induction coil as the test device, move back and forth along the direction of the standing wave in the wave section at the test does not produce sparks, the sparks wave of belly at the most. Measured using this method the length between the two waves of sections to determine the speed of electromagnetic waves is equal to the speed of light. In 1887 they designed the "induction balancer": about 1886 place a piece of equipment side of the metal plate D, and then the key of C so far there are no spark gap, then the metal plate D to move AB and C, C's spark gap has emerged. This is because the D out of the oscillating current induced in an additional electromagnetic field generated in C, close to the time when the D, C balance was destroyed. This experiment shows: Oscillator AB alternating the nearby medium changes the polarization and displacement current form, the displacement current will affect the "induction balancer C" of the balance. C appeared to spark. When D is close to C, the equilibrium is destroyed again, C spark again. Thus proved that the "displacement current" exists.
Hertz has to do with the metal surface to 45 ° angle of electromagnetic wave reflection; metal concave mirror to focus electromagnetic waves; metal gate so that the polarization of electromagnetic waves occur; and non-metallic materials with a large prism refraction of electromagnetic waves, etc. To prove that Maxwell's electromagnetic theory of light correctness. Thus Maxwell's electromagnetic theory was only the recognition. Been recognized as "self-Newton after the world's greatest mathematical physicist." Thus created by the Faraday, Maxwell established, proven Hertz electromagnetic theory to the world declared it a victory.