Electromagnetic radiation (EMR) is an energy that is copied by a certain electromagnetic process. Visible light belongs to electromagnetic waves, and electromagnetic waves such as radio waves, infrared rays, ultraviolet rays and X-rays are invisible to our eyes. In classical mechanics, electromagnetic radiation consists of electromagnetic waves composed of an oscillating electric field and a magnetic field at the same time. They are also delivered in vacuum at the speed of light. The two vibrations are perpendicular to each other and perpendicular to the direction of travel and transverse waves. Electromagnetic waves form an electromagnetic wave spectrum in the order of increasing or decreasing frequency, including radio waves, microwaves, infrared rays, visible rays, ultraviolet rays, X rays, and gamma rays. Electromagnetic waves occur when charged particles accelerate, which in turn interact with charged particles. In this process, electromagnetic waves can transmit energy, momentum and angular momentum. Both of the electromagnetic waves are photons. Photons have no mass but are affected by gravity. Electromagnetic radiation is a collection of electromagnetic waves that propagate freely into space without constant interaction with the particles (or currents) that create them. Therefore, the electromagnetic radiation is called the far field. Conversely, a near field refers to the particles that create it or the electromagnetic waves around the current. An example is static electricity or electromagnetic induction. Electromagnetic waves in quantum mechanics consist of photons, which are the fundamental particles involved in all electromagnetic interactions.
Quantum effects, such as blackbody radiation or quantum leap from atom to low energy level, provide an explanation for phenomena associated with specific electromagnetic radiation. The energy of individual photons is quantized and the larger the frequency of the photons, the greater the energy. This relationship is given by the Planck equation E = hf. Where E is the energy of the photon and f is the frequency of the photon. And h is Planck’s constant. For example, a gamma-ray photon delivers about 100,000 times more energy than a visible-light photon. The effect of electromagnetic radiation on biological systems (and chemical systems at many other standard temperature pressures) depends on the power and frequency of radiation. In the case of visible radiation or more electromagnetic radiation, the damage to cells or other matter is largely determined by the power, which is the result of the heating of a large number of photons from the summed energy. On the other hand, in the case of ultraviolet radiation or more energy-intensive electromagnetic radiation, chemical substances or living cells suffer more damage than simple heating. In the case of high-energy photons, individual photons directly affect the molecule. Contents 1 Physics 1.1 Theory 1.1.1 Maxwell’s Equation 1.1.2 Near field and far field Physics  The figure above shows the wavelength of the relative electromagnetic waves of three different colors of light (blue, green, red). The unit of x-axis is micrometer. Theory  Maxwell equation  Maxwell has introduced the wave equation of the electric field and the magnetic field to reveal the fluctuating nature of the electric field and the magnetic field, and also found their symmetry. Because the velocity of the electromagnetic wave predicted by the wave equation matched the velocity of the light measured, Maxwell concluded that the light was electromagnetic. The Maxwell equation was verified by experiments on Hertz’s radio waves. According to Maxwell’s equations, a spatially varying electric field always relates to a magnetic field that varies with time, and similarly, a temporally changing magnetic field is associated with an electric field that varies with space. The change in electric field in electromagnetic waves is accompanied by a magnetic field in one direction and vice versa. This relationship between the two is not one that induces another, but the changes of both, such as time and space, occur simultaneously and are deeply related to the theory of special relativity. In fact, the magnetic field can be regarded as a relativistic distortion of the electric field, and the relationship between them can be more than a metaphor for the change of time and space. The two together form an electromagnetic wave that extends into space and does not affect its origin. The electromagnetic field generated by the accelerating charge is transmitted through the space. Near-field and far-field  Maxwell’s equations show that charges and currents generate a certain type of electromagnetic field near them. It also behaves differently than electromagnetic radiation. The current directly forms a magnetic field, which is a magnetic dipole-like form in which the intensity decreases as the distance from the current increases. In a similar way, the electric charge moving by the voltage difference in the conductor forms an electric dipole shaped electric field, which also decreases with distance. They will form a near field. None of them make electromagnetic radiation. Instead, it is related to the behavior of a particular electromagnetic field within the transformer that transfers power near its source (moving charge or current), such as the electromagnetic induction or phenomenon that occurs near the coil of a metal detector. Usually the near field has a tremendous impact on their source. Each time energy is transferred from the electromagnetic field to the receiver, the electrical load on the source or transmitter increases (reactance decreases). However, if they do not extend into the outer space, but instead have no receptors, they will vibrate by returning energy back to the carrier. On the other hand, the far field is a copy that is transmitted without a transmission medium, ie, energy is needed to bring this field away from space at the source to create this far field. In such an electromagnetic field, the part far from the source is called electromagnetic radiation. This far field stretches without interaction with its source. They are independent in that there is an inherent energy independent of the carrier (source) or receptor. Generally, these waves extend in all directions from the source to the sphere in the absence of any obstacles. Thus, the energy of electromagnetic radiation reaching one point in the sphere follows the inverse square law. This is contrary to the near field near to the source. The near field is transmitted energy according to the inverse cubic law, and as the distance increases, the energy is not preserved and delivered. In other words, the farther the distance is, the less energy is transmitted, and the lost energy is returned to the source or delivered to a nearby receptor (such as the second coil of the transformer). The far field (electromagnetic radiation) and the near field have different mechanisms of occurrence and satisfy the different terms of Maxwell’s equations. The magnetic field portion of the near field is due to the source current, whereas the magnetic field of the electromagnetic radiation is due only to the local variation of the electric field. In a similar way, the electric field portion of the near field is due to the charge distribution of the source, whereas the electric field portion of the electromagnetic radiation is due to a local magnetic field change. The process of generating the electromagnetic field of electromagnetic radiation and the process of generating the near field electromagnetic field are different depending on the distance. This is why electromagnetic radiation can deliver a greater amount of energy than a near field at far distance from the source. Here, a sufficiently long distance means that the electromagnetic field that has already elapsed before the elapsed time elapses until the electric potential at the source changes and the electric field changes and the electromagnetic field of another phase extending outward is generated,