[Physics Class Notes] on Ultraviolet Radiation Pdf for Exam

Ultraviolet radiation lies on the electromagnetic spectrum that extends from the violet (short-wavelength), i.e., the end of the visible light range to the X-ray region. Ultraviolet (UV) radiation is imperceivable by our eyes, although, when it falls on certain materials, it may cause them to fluoresce a.k.a emit electromagnetic radiation of lower energy, such as visible light. Many insects like bees can see ultraviolet radiation.

In this article, we will learn about UV rays (UV radiation), the range of ultraviolet, and Ultraviolet light uses.

Ultraviolet Spectrum

The Range of Ultraviolet radiation is between 400 nanometres (1-nanometre or 10−9 meter) on the visible-light spectrum and about 10 nm on the X-ray side.

Although some authorities have extended the short-wavelength limit to 4 nm; however, in physics, ultraviolet radiation is divided into the following four regions:

1. Near – 400 to 300 nm 

2. Middle – 300 to 200 nm, 

3. Far 200 to 100 nm, and 

4. Extreme, i.e., below 100 nm). 

Types of UV Rays

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Ultraviolet light is also known as UV light is one of the types of electromagnetic radiation that emits from the sun and gets transmitted at varying wavelengths and frequencies. On the electromagnetic spectrum, UV light falls between visible light and X-rays (as we discussed above) and it can be divided into UVA or near UV, UVB or middle UV, and UVC or far UV.

Based on the interpretation of wavelengths of ultraviolet radiation with biological materials, three types of UV rays are as follows: 

1. UVA Rays – Wavelength ranges from 400 to 315 nm. UVA is also called blacklight.

2. UVB Rays –  Wavelength ranges from 315 to 280 nm. UVB Rays are well-known for the hazardous effects of radiation on organisms.

3. Ultraviolet C Light –   Wavelength ranges from 280 to 100 nm. The UV rays do not reach Earth’s surface. However, they are very harmful and cause skin cancer and many health issues.

UV Radiation

UV radiation is created by very hot surfaces, like the Sun, in a continuous spectrum.

Ultraviolet waves are produced by atomic excitation in a gaseous discharge tube as a discrete spectrum of wavelengths. 

Most of the UV radiation in sunlight gets absorbed by oxygen in Earth’s atmosphere that forms the ozone layer at the lower stratosphere. Out of the 99% Ultraviolet rays that do reach Earth’s surface, almost 99 percent are UVA rays.

UVB Rays

When the ozone layer becomes thin or the ozone layer depletion occurs, more UVB radiation reaches Earth’s surface and causes harmful effects on organisms. 

For instance, many studies have shown that UVB radiation crosses the oceanic surface and is lethal to marine plankton to a depth of 30 meters, i.e., around 100 feet in clear water. 

Do You Know?

Marine scientists discovered that a rise in UVB rays levels in the Southern Ocean from the year 1970 to 2003 was strongly associated with a continuous decline in fish, krill, and other marine life.

Now, let’s discuss the Ultraviolet Uses:

Uses of UV Rays

Ultraviolet light uses range from medical therapy to photography. Now, let’s discuss some uses of Ultraviolet rays in detail:

Tanning

While walking on hot days, our skin gets exposed to UVB rays, the body’s innate defense system kicks in, and therefore, generates a pigment known as melanin. This melanin absorbs UV light and spreads it as heat. Your skin gets darker because the body sends a signal as melanin into the surrounding cells to prevent skin damage. However, tanning booths use artificial UV light in lamps that pass electric currents via a gas such as a vaporized mercury.

Lamps

Many natural and recreational substances can absorb UV radiation, like plants, fungi, and synthetic fluorophores. When the UV rays are absorbed, the electrons in the material reach a higher energy state, and before reaching their power level gradually in a step-by-step fashion release some of their absorbed energy as visible light. 

Fluorescent lamps ionize vapor in their tubes, thus electrons in the gas emit photons at the Ultraviolet spectrum frequencies.

For example, a phosphor layer on the inner core of the tube changes the UV rays to a standard visible light.

Chemistry

Many scientists use UV rays to analyze and study the chemical composition and structure of compounds through color variations. A mechanism called spectroscopy employs a device, viz: spectrophotometer that is much more sensitive to color than our eyes. 

A beam of Ultraviolet light is passed through a solution and a spectrometer shows how much UV light is absorbed by a compound using color changes.

The same method is applied to chemicals, biological plants. Hospitals, water quality control labs, petrochemical, and food industries.

For instance, it can display unwanted compounds residing in water by monitoring the color of water during the drinking water production process.

Photography

UV photography is used in medical, scientific fields, and forensic labs. It uses certain lenses to let UV rays pass via the lenses of a camera. 

Nature photographers use UV photography to capture patterns in flowers that are unperceivable to our eyes. By modifying their camera, they can gather the UV light that strikes the camera sensor.