TELECOMMUNICATIONS

If we go back to the times when mail was the only method to transmit information, we will realize the importance of telecommunications: staying together in the distance is something that goes beyond the sentimental. The development of science and society depends on the dialogue of many people and the transmission of ideas.

source

The artificial communications satellites capture the electromagnetic waves of the transmitters and transmit them to huge areas of the planet

If the information is not transmitted fluently, the development is delayed and the evolution stagnates. This is already sufficient justification for the property that in our society is given to telecommunications and the efforts that are devoted to its development. Its start we owe to a physicist named Hertz. He was the first to experiment with a new concept that led to the development of modern communication at a distance and then we discover: electromagnetic waves.

Electromagnetic waves

We must remember that charged particles create an electric field around them and, depending on the circumstances, a magnetic field. From now on to the union of both we will call it electromagnetic field.

The next thing we will do is to consider how qualitatively affects the movement of charges to the field. We saw that the field took in each point of the space a value that depended on the distance of the load to the point. If the load moves, the distance of the load to any point will be affected and, therefore, the value of the field will vary.
How will the field vary? The possibilities that we have are two: the change of position of the load could cause the value of the field in all the space automatically, or the change could take a certain time to take effect. Experimentally it is verified that the correct option is the second one. The change is transmitted at a given speed that turns out to be that of light (300.00 km / s). Thus, a point located 300,000 km from the load will take 1 s to perceive the movement of the load; another located at 600,000 km will take 2 s, and so it can be easily calculated for any distance. This is an observable effect for long distances since, for 300 km, the delay will be just one thousandth of a second, and we can practically disregard it. It can be verified that the variation in the electromagnetic field is transmitted just like a wave that moves at the speed of light. We will call, then, electromagnetic waves to the transmission of the variation of the field, and we will say that the movement of the charges causes electromagnetic waves that move at the speed of light.
The fact that the speed of these waves is that of light is not a coincidence; in fact, light is nothing more than an electromagnetic wave. The microwaves, the X-rays, the ultraviolet, they are all electromagnetic waves. The only difference between them is the wavelength, already explained in the topic dedicated to waves, which gives them different properties according to their value. To study the way these waves are used in telecommunications, we focus on the use that is given to them in the two most widespread media: radio and television.

Radio

If we grab a stretched paper and talk in front of it we can see that it vibrates. The microphone uses this same principle: when we speak in front of one, we vibrate a membrane that transforms its vibrations into an electric current. The current thus generated, in some way, encoded the information of our voice along with what we said. This current causes in the antenna of the transmitter a movement of charges that produces electromagnetic waves, as we discussed previously.

source

Radio devices capture electromagnetic waves and transform them into sound.
The generated waves are transmitted through space to the antenna of our receivers, which convert the waves back into a new electric current. This, like the first, contains the information of the voice that originated it. To recover, we pass the current through a coil inside which is a metal piece. The induced intensity will not be constant, but will vary and will cause changes in the magnetic field inside the coil. As a result, the metal piece will move to one side and another hitting a small membrane that will reproduce the sound that initially caught the microphone of the station. We just need to amplify it and enjoy our favorite station.

Television

source

The transmission of information is basically the same for radio as for television; The essential difference lies in the way it is transformed into images.
Inside the televisions is a device called electron gun, which emits these particles with more or less energy as necessary. The electrons are emitted in a straight line, but some magnets deflect them and make them reach all the points of the screen, giving them a color that depends on the energy with which the cannon emitted them. A multitude of images are thus formed one behind the other that our eyes capture as a continuous movement, and the electromagnetic waves of the transmitters are those that "tell" the device the energies with which the electrons must emit at each moment.
We see in this way how, with a little imagination, applications can be designed that make communication possible over long distances from simple principles such as electromagnetic waves.