Hardness is indirectly related to: specific gravity surface roughness strength of chemical bonds weight
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Let's begin by explaining that the <u>electromagnetic spectrum</u> is the set of electromagnetic radiations distributed in their different frequencies or wavelengths. So, if we go from the smallest wavelengths known up to now (because according to physics the electromagnetic spectrum is infinite and continuous) to the longest, the electromagnetic spectrum covers the following radiations:
Gamma rays, X-rays, ultraviolet, visible light, infrared, radio waves and microwaves:
-Gamma rays: With a wavelength in the order of , is a type of ionizing radiation capable of penetrating matter quite deeply and is able to cause serious damage to the nucleus of the cells.
-X rays: With a wavelength between and
. It is invisible to the human eye, capable of crossing opaque bodies and is also an ionizing radiation.
-Ultraviolet light (UV): Whose wavelength is approximately between 100 nm and 380 nm; is a type of electromagnetic radiation that is not visible to the human eye.
-Visible light: This part of the spectrum is located between ultraviolet light and infrared light (400 nm - 800 nm). It should be noted, the fact the only part of the whole electromagnetic spectrum is visible to humans is because the receptors in our eyes are only sensitive to these wavelengths.
-Infrared: This type of radiation is not visible to the human eye, since its wavelengths are outside the visible spectrum (between 700 nm and 1 mm).
These waves can be divided into:
- Near infrared or long wave infrared: it is the least sensitive to color and is easily absorbed by water.
- Medium or medium wave infrared: it is also insensitive to color and easily absorbed by water and many types of plastics and paints.
- Far infrared or short wave infrared: it is more penetrating than the long wave and is good for heating metals, these waves also can pass through clear materials.
This light has many uses, including heating lamps in physiotherapy and medical treatments, heat sensing devices, among others.
-Radio waves: This is a type of electromagnetic radiation with wavelengths between 10 m to 10,000 m. This type of electromagnetic waves is very well reflected in the ionosphere, the layer of the atmosphere through which they travel directly or using repeaters. In addition, this radiation is important in telecommunications.