In 1865, the famous English physicist J. Maxwell, based on the results of the work of Faraday on the study of the electromagnetic field, was able to theoretically justify the possibility of the existence of such fields in the absence of currents and charges that generated them. The field configuration outside the source is a wave. Studying the properties of electromagnetic waves, one cannot fail to notice an interesting fact: the propagation velocity depends on the medium. For example, in a vacuum it is about 300 thousand km / s. Since this value corresponds to the speed of light, this allowed Maxwell to assume that light is one of the varieties of electromagnetic waves. This was further confirmed by the experiments of Hertz. Before the advent of Maxwell's theory, it was believed that visible light, x-rays, ultraviolet, radio are unrelated radiation. In fact, the properties of the waves depend on their length. The whole spectrum was conditionally divided into regions, each of which has its own manifestations.
The properties of electromagnetic waves are unique, since their general interaction with matter is immediately explained by two components - magnetic and electrical. Thus, in an electromagnetic wave, which is not affected externally, both fields oscillate in their directions and planes, moreover, perpendicular to the direction of propagation of the wave itself. The basic properties of electromagnetic waves are represented by many manifestations, regardless of the nature of the source. Let's consider some of them. It is much more convenient to present real experience, so we mentally use two devices - a directional radiation generator and a receiver. As already indicated, the results are applicable to any type of wave. Knowing the properties of electromagnetic waves, they can be controlled in the desired way.
In everyday life, each of us is faced with reflection every day. For example, sometimes, in order for a mobile phone to lose contact with the base station, it is enough to go into a room with thick reinforced concrete walls or even into a regular house elevator. Returning to the experiment: if the generator and the receiver are positioned at an angle to each other, the signal will not be recorded (directional emitter). But it’s worth placing a metal plate at the intersection of two conditional lines (directional vectors), as the receiver will pick up the radiation, that is, there is reflection. Similar properties of electromagnetic waves are formulated in the statement on the equality of the angles of incidence and reflection.
The next property is refraction. When the receiver and the directional emitter are at different heights, the signal will not be picked up. But if you place a paraffin cube between them, then the whole scheme works. This is due to a change in the direction of wave propagation at the boundary of two dielectric media (paraffin and air).
Further, interference is worth mentioning. If two metal plates are placed in close proximity to one another, forming an angle slightly less than 180 degrees, then when a radio wave is emitted on these sheets, the receiver will notice a difference in their intensity depending on its location relative to the sheets. A well-known example is a satellite dish. It is the “plate” that amplifies the signal by collecting scattered waves and concentrating them on the receiver.
Another known property is diffraction. In part, thanks to her, she manages to use radios. The following experience: we place a metal plate between the generator and the receiver, and the distance between them is minimal. As a result, the signal is absent, since it is reflected back from the plate, towards the generator. But if the generator and receiver are spaced apart from the plate, a signal will appear. This happens due to the property of waves to go around obstacles.