The electromagnetic spectrum consists of the ordered arrangement of all wavelengths of electromagnetic waves, which assume any positive value, without any restriction. It is divided into 7 sections, including visible light.
We are familiar with the frequencies of visible light when we see the rainbow, in which each color corresponds to a different wavelength: red is the longest and violet the shortest.
Electromagnetic spectrum. Note that the frequency (and with it the energy) increases from left to right in this scheme. André Oliva / Public domain
The visible light range only occupies a very short area of the spectrum. The other regions, which we cannot see, are radio waves, microwaves, infrared, ultraviolet, X-rays, and gamma rays.
The regions were not discovered at the same time, but at different times. For example, the existence of radio waves was predicted in 1867 by James Clerk Maxwell and years later, in 1887, Heinrich Hertz produced them for the first time in his laboratory, which is why they are called Hertzian waves.
All are capable of interacting with matter, but in different ways, depending on the energy they carry. On the other hand, the different regions of the electromagnetic spectrum are not sharply defined, because in fact the boundaries are fuzzy.
Bands
Bands of the electromagnetic spectrum. Tatoute and Phrood / CC BY-SA (http://creativecommons.org/licenses/by-sa/3.0/)
The boundaries between the different regions of the electromagnetic spectrum are rather fuzzy. These are not natural divisions, in fact the spectrum is a continuum.
However, the separation into bands or zones serves to conveniently characterize the spectrum according to its properties. We will begin our description with radio waves, whose wavelengths are longer.
Radio waves
The lowest frequencies have a range around 10 4 Hz, which in turn correspond to the longest wavelengths, typically the size of a building. AM, FM and the citizens band radio use waves in this range, as well as VHF and UHF television broadcasts.
For communication purposes, radio waves were used for the first time around 1890, when Guglielmo Marconi invented the radio.
As the frequency of radio waves is lower, they have no ionizing effects on matter. This means that radio waves lack enough energy to eject electrons from molecules, but they do increase the temperature of objects by raising the vibration of the molecules.
Microwave oven
The wavelength of microwaves is on the order of centimeters and they were also first detected by Heinrich Hertz.
They have enough energy to heat food, which to a greater or lesser extent contains water. Water is a polar molecule, which means that although it is electrically neutral, the negative and positive charges are slightly separated, forming an electric dipole.
When microwaves, which are electromagnetic fields, strike a dipole, they produce torques that make them rotate to align them with the field. The movement translates into energy that spreads through the food and has the effect of heating it.
Infrared
This part of the electromagnetic spectrum was discovered by William Herschel in the early 19th century and has a lower frequency than visible light, but higher than microwaves.
The wavelength of the infrared spectrum (below red) is comparable to the tip of a needle, therefore it is a more energetic radiation than microwaves.
Much of the solar radiation comes at these frequencies. Any object emits a certain amount of infrared radiation, especially if they are hot, such as kitchen burners and warm-blooded animals. It is invisible to people, but some predators distinguish the infrared emission from their prey, giving them an advantage in hunting.
Visible
It is the part of the spectrum that we can detect with our eyes, between 400 and 700 nanometers (1 nanometer, abbreviated nm is 1 × 10 -9 m) of wavelength.
White light contains a mixture of all wavelengths, which we can see separately when passed through a prism. Raindrops in clouds sometimes behave like prisms, so we can see the colors of the rainbow.
The colors of the rainbow represent different wavelengths of visible light. Source: Pixabay.
The wavelengths of the colors we see, in nanometers, are:
-Red: 700–620
-Orange: 620–600
-Yellow: 600–580
-Green: 580–490
-Blue: 490–450
-Violet: 450–400
Ultraviolet
It is a more energetic region than visible light, with wavelengths beyond violet, that is, greater than 450 nm.
We cannot see it, but the radiation that comes from the Sun is very abundant. And as it has higher energy than the visible part, this radiation interacts much more with matter, causing damage to many molecules of biological importance.
Ultraviolet rays were discovered shortly after infrared rays, although at first they were called "chemical rays", because they react with substances such as silver chloride.
X-rays
They were discovered by Wilhelm Roentgen in 1895 while experimenting with accelerating electrons (cathode rays) directed at a target. Unable to explain where they came from, he called them X-rays.
It is a highly energetic radiation with a wavelength comparable to the size of the atom, capable of passing through opaque bodies and producing images as in X-rays.
Radiographs are obtained using X-rays: Source: Pixabay.
As they have more energy, they can interact with matter by extracting electrons from molecules, hence they are known by the name of ionizing radiation.
Gamma rays
This is the most energetic radiation of all, with wavelengths on the order of an atomic nucleus. It occurs frequently in nature, as it is emitted by radioactive elements as they decay to more stable nuclei.
In the universe there are sources of gamma rays in supernova explosions, as well as mysterious objects among which are pulsars, black holes and neutron stars.
The Earth's atmosphere protects the planet from these highly ionizing radiations that come from the universe, and due to their high energy, they have a harmful effect on biological tissue.
Applications
-Radio waves or radio frequencies are used in telecommunications, because they are capable of transporting information. Also for therapeutic purposes to warm tissues and improve skin texture.
-To obtain magnetic resonance images, radiofrequencies are also required. In astronomy, radio telescopes use them to study the structure of celestial objects.
-Cell phones and satellite television are two applications of microwaves. Radar is another important application. In addition, the entire universe is immersed in a microwave radiation background, coming from the Big Bang, being the detection of said background radiation the best proof in favor of this theory.
The radar emits a pulse towards an object, which disperses the energy in all directions, but part of it is reflected, bringing information about the object's location. Source: Wikimedia Commons.
-Visible light is necessary as it allows us to interact effectively with our environment.
-X-rays have multiple applications as a diagnostic tool in medicine and also at the level of materials science, to determine the characteristics of many substances.
-Gamma radiation from different sources is used as a treatment for cancer, as well as to sterilize food.
References
- Giambattista, A. 2010. Physics. Second Edition. McGraw Hill.
- Giancoli, D. 2006. Physics: Principles with Applications. 6th. Ed Prentice Hall.
- Rex, A. 2011. Fundamentals of Physics. Pearson.
- Serway, R. 2019. Physics for Science and Engineering. 10th. Edition. Volume 2. Cengage.
- Shipman, J. 2009. An Introduction to Physical Science. Twelfth edition. Brooks / Cole, Cengage Editions.