[Physics Class Notes] on UV Light Pdf for Exam

What Are UV Rays?

The term UV light or UV rays has been a familiar term for us. Here we will get to know the details of this term. What is UV light or what are UV rays? The full form of UV in UV rays is ultraviolet. Ultraviolet means “beyond violet”. In visible light, the color violet has the highest frequency. Ultraviolet has a higher frequency (and thus a shorter wavelength) than violet light. Its wavelength ranges from 10nm to 400nm. The corresponding frequencies are approximately 30 PHz to 750 THz. Its wavelength is shorter than that of visible light but longer than X-rays. Sunlight contains UV light and constitutes around 10% of the total electromagnetic radiation output from the sun. In 1801 a German physicist Johann Wilhelm Ritter discovered UV radiation.

Ultraviolet radiation is basically a type of electromagnetic radiation. These rays are a part of energy coming from the sun. These rays are quite harmful to us but are stopped by the earth’s ozone layer from entering the earth’s atmosphere. These rays are invisible to most of the humans as the human eye lens blocks the rays of wavelengths ranging from 300nm to 400nm and the shorter wavelengths are blocked by the ‘cornea’ of the eye. Also, we lack colour receptor adaptation for UV rays. However, some children or young adults might be able to these rays of lower wavelength. Also, some insects and mammals can see these radiations. Electric arcs and specialized lights, such as mercury-vapor lamps, tanning lamps, and black lights also produce it.

Types of UV Rays

The UV ray spectrum is broadly classified into three major divisions. However, there are some other subdivisions as well. We can see the divisions in the table given below.

Other Subdivisions Are

Suitable photodiodes and photocathodes can detect ultraviolet. These are sensitive to different parts of the UV spectrum. Sensitive ultraviolet photomultipliers are also used. The measurement of UV radiation is done by spectrometers and radiometers. Silicon detectors are also used across the spectrum.

• UVA is the type that reaches the most to us on earth’s surface hence not affected by ozone.

• It is a black light and called soft UV.

• Since it reaches us hence can cause skin cancer called melanoma.

• UVB is highly affected by ozone as only 1.3% of it reaches the earth’s surface.

• It is responsible for tan and skin burns.

• It is called intermediate UV.

• It is stimulated for the production of vitamin D.

• UVC is completely absorbed by ozone and atmosphere and most of it is scattered.

• It is hard UV.

• It causes lesions on the skin.

• H Lyman-α is ionizing radiation at shorter wavelengths.

• The specific wavelength of VUV can propagate through nitrogen but most of it is strongly absorbed by atmospheric oxygen.

• EUV is completely absorbed by the atmosphere and is strong ionising radiation.

What is UV Light Used For?

UV light has the ability to cause chemical reactions and excite fluorescence in materials, so it has a wide range of applications.

• UV is useful in photography using different filters and different lenses for different wavelengths. Some cameras are also designed for use in UV. Medical, scientific, and forensic investigations use photography by reflected ultraviolet radiation in applications as widespread as detecting bruising of the skin, alterations of documents, or restoration work on paintings.

• UV light has important uses in the electrical and electronics industry. On an electrical apparatus, corona discharge is detected by its ultraviolet emissions. Erasable programmable read-only memory (EPROMS) is erased on exposure to this light.

• UV light also finds its use in fluorescent dyes. Optical brighteners to papers and fabrics are colourless fluorescent dyes emitting blue light under UV. Glowing UV fluorescent dyes are used in textiles,  paints, papers, and other art and aesthetic applications.

• Irrespective of the structure or colour of the surface the bodily fluid is deposited upon UV is helpful in locating and identifying bodily fluids as blood, semen, saliva. Hence, it finds an important role in crime scenes and helps in tests performed at forensic laboratories.

• UV light is widely used in sterilization and disinfection. In medical and biological laboratories, UV lamps are used to sterilize the work area. UV radiation is used for disinfection in waste-water treatment.

• UV radiation is used in the therapy of some skin conditions as psoriasis and vitiligo.