Physics Ideas

# Electromagnetic spectrum: characteristics, bands, applications

The electromagnetic spectrum consists of the ordered arrangement of all wavelengths of electromagnetic waves, which assume any positive value, without any restrictions. It is divided into 7 sections including visible light.

We are familiar with the frequencies of visible light when we see the rainbow, where each color corresponds to a different wavelength: red is the longest and violet is the shortest.

The visible light range barely occupies a very short area of ​​the spectrum. The other regions 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 blurred.

## bands

The boundaries between the different regions of the electromagnetic spectrum are quite confusing. 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 start our description with radio waves, whose wavelengths are longer.

The lower frequencies have a range around 10 4 Hz, which in turn corresponds to the longer wavelengths, usually the size of a building. AM, FM and Citizen Band radios use waves in this band, as well as VHF and UHF television broadcasts.

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For communication purposes, radio waves were first used around 1890, when Guglielmo Marconi invented 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 increase the temperature of objects by increasing the molecules’ vibration.

### microwave

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 degree, 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 electrical dipole.

When microwaves, which are electromagnetic fields, hit a dipole, they produce torques that spin them to align them with the field. The movement translates into energy that spreads through the food and has the effect of heating it up.

### Infra-red

This part of the electromagnetic spectrum was discovered by William Herschel in the early 1800s 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, so it is more energetic radiation than microwaves.

Much of the solar radiation occurs at these frequencies. Any object emits a certain amount of infrared radiation, even more so if it is hot, for example, kitchen stoves and warm-blooded animals. It’s invisible to people, but some predators distinguish their prey’s infrared emission, 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, short nm is 1 × 10 -9 m) in wavelength.

White light contains a mixture of all wavelengths, which we can see separately when passed through a prism. Sometimes the water droplets in the clouds behave like prisms and that’s why we can see the colors of the rainbow.

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, ie, greater than 450 nm.

We can’t see it, but the radiation coming from the sun is very abundant. And, as it has more 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, although they were originally called “chemical rays” because they react with substances like silver chloride.

### X ray

Wilhelm Roentgen discovered them 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 an atom, capable of passing through opaque bodies and producing images as in radiographs.

As they have more energy, they can interact with matter by extracting electrons from molecules, so they are known as ionizing radiation.

### Gamma

This is the most energetic radiation of all, with wavelengths on the order of an atomic nucleus. It often occurs in nature as it is emitted by radioactive elements as they decay into more stable nuclei.

In the universe, there are gamma-ray sources in supernova explosions, as well as mysterious objects, including pulsars, black holes and neutron stars.

The Earth’s atmosphere protects the planet from these highly ionizing radiations which come from the universe and which, due to their great energy, have a detrimental effect on biological tissue.

## Forms

– Radio waves or radio frequencies are used in telecommunications because they are capable of carrying information. Also for therapeutic purposes, to warm tissues and improve skin texture.

-To obtain MRI images, radio frequencies are also required. In astronomy, radio telescopes use them to study the structure of celestial objects.

Cell phones and satellite television are two microwave applications. Radar is another important application. Furthermore, the entire universe is immersed in a background of microwave radiation from the Big Bang, and the detection of such background radiation is the best test in favor of this theory.

Visible light is necessary as it allows us to effectively interact with the environment.

X-rays have multiple applications as a diagnostic tool in medicine as well as 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.