ULTRAVIOLET RAYS

ultraviolet rays

INDEX

3) INTERESTING ASPECTS

1) WHAT ARE ULTRAVIOLET RAYS?

5) SITOGRAPHY

BANDS

In physics

human eye

SOLAR ULTRAVIOLET

biological effects

UV CHEMISTRY

ASTRONOMY

2) THE STORY

4) APPLICATIONS

DISCOVERY

ELECTRONICS

PHOTOGRAPHY

GERMICIDAL ULTRAVIOLET RADIATION

WHAT ARE ULTRAVIOLET RAYS?

IN PHYSICS

Ultraviolet radiation is a range of electromagnetic radiation, belonging to the electromagnetic spectrum, with a wavelength immediately shorter than the light visible to the human eye and immediately higher than that of X-rays.

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human eye

Ultraviolet rays are invisible to humans. The human eye normally does not perceive light with a wavelength lower than 390 nm. However, there are exceptions: under certain conditions, children and teenagers can perceive ultraviolet up to 310 nm. The lens, in general, filters UVB or higher frequencies, but people suffering from pathologies such as aphakia (absence of the lens) can also see in the UV band.

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biological effects

The biological effects of UV, due to their interaction with organic molecules, are responsible for phenomena such as:

-tanning; -freckles; -sunburn;

They also represent the main cause of skin cancer. Any living organism would be seriously damaged by UV rays coming from the Sun if a good part of the radiation was not filtered by the Earth's atmosphere. A low wavelength of ultraviolet, below 121 nm, ionizes the air so rapidly that it is almost completely absorbed before it reaches the ground.

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THE STORY

Discovery

Ultraviolet radiation was discovered in 1801, when German physicist Johann Wilhelm Ritter noticed that silver chloride was photosensitive, meaning it turned dark in the presence of "invisible rays" (UV) just below the violet end of the visible spectrum. He called them "oxidation rays" to emphasize the chemical reaction and distinguish them from infrared rays, discovered the year before at the other end of the visible spectrum.

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INTERESTING ASPECT

BANDS

UV can be divided into different bands, defined differently depending on the fields of study. The most immediate subdivision is: -Near UV (380-200 nm) and extreme UV (200-10 nm).

When considering the effect of UV rays on human health, the UV wavelength range is typically divided into: -UV-A (400-315 nm), UV-B (315-280 nm) and UV-C (280-100 nm).

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SOLAR ULTRAVIOLEt

Very hot objects, due to blackbody emission, emit UV radiation.

Sunlight in the Earth's outer atmosphere is composed of approximately 50% infrared light, 40% visible light and 10% ultraviolet light, for a total intensity of approximately 1400 W/m2 in vacuum.

The percentages of sunlight reaching the Earth's surface become: 44% visible light, 3% ultraviolet when the Sun is at its highest point in the sky (zenith) and the remaining infrared.

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UV CHEMISTRY

UV radiation leads to UV degradation of organic materials. To prevent this decay, molecules capable of absorbing part of the radiation are used. In turn, they can suffer the negative effects of UV, making it necessary to periodically check their ability to absorb the radiation.

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ASTRONOMY

Very hot celestial bodies mainly emit ultraviolet light (Wien's law). It is difficult to observe this light from the ground, because the ozone layer blocks most of it. So almost all UV observations are conducted in space, using satellites carrying telescopes and detectors operating in the ultraviolet.

APPLICATIONS

ELECTRONICS

-Fluorescent lamps exploit the ultraviolet emission of mercury at low pressure. A fluorescent coating inside the tube absorbs UV and turns it into visible light;-Ultraviolet lamps are used to analyze minerals, gems and in the identification of various collectibles; -Ultraviolet lamps are also used to purify water and to sterilize environments and instruments used in hospitals and biological laboratories, because they kill almost all viruses and bacteria.

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PHOTOGRAPHY

Photographic film responds to ultraviolet radiation, but glass camera lenses typically block radiation below 350 nm. UV blocking filters, having a yellow tint, are often used for outdoor photography to avoid washed out images and excessive exposures due to UV rays. For photography near UV, special filters can be used.

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GERMICIDAL ULTRAVIOLET RADIATION

Germicidal ultraviolet radiation is ultraviolet radiation which is characterized by a band of wavelengths capable of destroying bacteria, viruses and other microorganisms, modifying their DNA or RNA and therefore inactivating them and preventing their reproduction. This principle allows the disinfection of water and air.

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THANKS!

sources:https://it.wikipedia.org/ https://www.focus.it/ and materials provided in class

work carried out by: Cristina Marcheggiani