Visible Light, X-rays and UV Rays - Term Paper Example

 Visible Light, X-rays and UV rays The electromagnetic spectrum is divided into eight (Terahertz radiation has been included in the list recently) different rays based on their wavelength or frequency. Most parts of this spectrum is of great use to Science. Previously there was only “light” but the presence of other electromagnetic radiations surfaced when in 1800 William Herschel discovered infrared radiations. Since then for decades researchers have devoted time and energy to determine everything about the electromagnetic spectrum in detail. Visible light rays, X-rays and UV rays are three of the seven electromagnetic waves. VISIBLE LIGHT The visible light ray is the sole electromagnetic wave that can be perceived by us. The visible light itself is made up of seven constituent colors. These are the colors that we see in the rainbow (VIBGYOR). Newton was the first one who proved that visible light is constituted of colors. The wavelength of visible light lies between 400 nm – 700nm. The constituent colors of the visible light can be obtained if it is passed through a prism. Visible light obeys laws of Reflection and refraction and phenomenon of dispersion and interference can also be observed as well. Visible light is emitted during the process of transition of atoms. Visible light can be detected by photographic emulsion, photo sensitive cells and eyes. The light helps us in vision but its uses do not end here, it is utilized in communication as well. Communication with the help of visible light is known as VLC (Visible Light Communication). VLC uses LED or simple fluorescent lamps to transmit signals to long distances. These signals are detected and received by special electronic devices which contain diodes. The diodes in turn transform the light signals to electrical pulses. A.G. Bell was the first one to demonstrate this idea through his Photophone. The use of LED light was started in 2003. Since visible light has negligible effect on our eyes when compared to other rays it is the best option for such communication system. According to an article in Journals of Materials Chemistry, some researchers at the University of Illinois have come up with a disinfecting process for which previously harmful UV rays had to be used. This disinfecting process uses visible light to destroy bacteria and viruses. For this the researchers used a nitrogen-doped titanium-oxide matrix which had had palladium nano particles which allows hydroxyl ions to kill bacteria and viruses. X-RAY X-rays were discovered by W.C. Roentgen, quite by chance. Such a “by chance discovery” is known as Serendipity in scientific terminology. While working in his laboratory to produce cathode rays using Crookes tube he noticed the phenomenon of fluorescence in a barium platinocyanide screen which was kept some distance away. The year was 1895 and Roentgen named his newly found rays –“X-rays” (X meaning unknown). In the electromagnetic spectrum, X-rays occupies the range between UV rays and gamma rays. The wavelength of X-rays lies between 10 nm- 0.001 nm. X-rays do not contain any particles. X-rays having long wavelengths are known as soft X-rays while those having shorter wavelength are known as hard X-rays. Mechanically, X-rays can be produced using an X-ray tube which was invented by Dr. Coolidge in 1913. The tube consisted of an evacuated glass bulb containing a cathode and an anode at the extreme ends inside the bulb. A high voltage was applied which developed a strong electric field between the cathode and the anode which resulted in the ionization of gas molecules. The cathode plate released cathode rays when it was hit by positive ions. The cathode ray is nothing but a stream of electrons. These electrons were attracted by the positive anode and they accelerated towards it. In this process they produced X-rays. This was the very first model of tube used to produce the rays. In modern tubes X-rays are produced by two mechanisms- Bremsstrahlung and Characteristic radiation mechanisms. In the laboratory, the rays maybe used to study the atomic structure or any crystalline structure in details but the maximum benefits of this discovery has been reaped by Medical science. It was noticed that X-rays could be blocked by bones and partially blocked by vital organs. Thus, X-rays was used by physicians to study human anatomy and treat health problems. Soon enough, with greater advancement, X-rays were used to treat tuberculosis, tonsils and even cancer. Thus the branch of Radiology had grown manifolds and is still growing because of the chance discovery of X-rays. The properties of X-rays are so varied that an entire branch namely X-ray optics has been developed to study everything about these rays. UV RAYS UV rays stands for ultra-violet radiation. The wavelength of UV rays lies between 10 nm- 400 nm. Though human eyes cannot perceive UV rays but it is perceive by some arachnids, mollusks and the avian population. J.W Ritter was the first one to notice that silver salts changed color faster when exposed to visible light. The term Ultra-violet was used because in the visible spectrum, violet color has the shortest wavelength but UV rays have wavelengths shorter than that of violet light. The sun emits UV radiations while artificially they may be produced by black lights, ultraviolet LED, gas-discharge lamps, ultraviolet lasers etc. Researchers have classified UV into three types- UV- A, UV-B and UV-C. Photobiologist and environmentalists have defined the individual wavelengths of all the three types of ultraviolet radiation. The wavelength of UV-A lies between 400-320 nm, while the wavelength of UV-B lies between 320-290 nm and that of UV-C lies between 290-200 nm. Out of all three, UV-C is absorbed by the ozone layer that surrounds the earth; however, the other UV radiations are not absorbed and freely reach the surface of the earth. Since UV rays can penetrate deep into the human body, it considered harmful. In fact, one of the primary concerns about ozone layer depletion was the complete, unprotected exposure to harmful cosmic rays. Research in the early 1980’s showed that if the ozone layer was destroyed due to over use of CFC’s etc UV rays would not be absorbed. UV rays are used in laboratories for disinfection purposes. It kills bacteria and viruses that may interfere with an experiment. This germicidal property of UV has been used by the food industry and also for water treatments since the rays do not add any color, odor and taste, but merely gets rid of harmful micro-organism, chlorine reduction and water ozone destruction. UV rays are also used to detect forged notes in the bank because real notes issued by bank have some incorporated fluorescent dyes which glow when exposed to UV radiation. The rays are also utilized to determine the authenticity of antique pieces. Though UV is known to be harmful for skin but controlled exposure to UV is used to treat a number of skin problems like Psoriases, vitiligo, acne etc. Distinction between Visible, UV and X-rays There are ways to differentiate between these 3 types of electromagnetic radiation because owing to their differences in wavelength, each ray has its unique set of properties. Visible radiations are produces during transition of atomic particles while, while X-rays are produced by atoms during electron transition, particle acceleration and deceleration. UV rays are also produced during atomic transitions. The wavelength of visible light is between 400 nm- 700 nm while the wavelength of X-rays is between 10 nm – 0.001 nm. The wavelength of UV rays lies between that of visible light and X-Ray radiation and ranges between 10 nm – 400 nm. While both X-rays and UV rays are ionizing radiation, visible rays are non-ionizing radiation. This means that both X-rays and UV rays carry high amount of energy per quantum to ionize the medium through which they pass whereas visible light does not have enough energy to cause ionization in the medium. Thus, it is also evident from here that these three have different amount of energy. While X-rays have the highest amount of energy among the three, UV comes next in the list, followed by visible light. The effect that visible light may have on the skin is not really clear.. At first it was believed that visible light has no ill-effects on the skin at all. However, according to an article published in PubMed, the advancement in the study of skin optics has determined that visible light causes skin pigmentation, erythema and helps produce of harmful free radicals. The visible light effect is still under study. However, the ill-effects of X-rays and UV rays have been studied to a great extent. X-rays are highly penetrating and have harmful effects on the body such that even a short span of exposure to X-rays causes reddening of the skin, while long and extended exposure will kill the body cells and tissues. The worst among the three is definitely the ultraviolet radiations because both its short term effects as well as long terms effects are equally harmful. The short term exposure to UV rays causes tanning and sunburn (pigmentation of epidermal layer. Short term exposure also causes Welder’s flash in the eye which is a sensation of constant irritation in the eye. Long term exposure to these rays include photoaging (premature aging), cataracts, retinol burns which results in the loss of vision and skin cancer. Visible light obeys the laws of reflection, refraction and undergoes diffraction. X-rays have a very low refractive index when compared to that of visible light (slightly less than unity) and is not reflected by ordinary mirrors. These properties of X-rays have led to the production of X-ray telescopes and X-ray microscopes. UV rays can also be reflected and refracted to some extent. All the three, i.e. Visible light, X-rays and ultraviolet light rays travel in straight line ( overlooking the dual nature of light) but the velocities of the X-rays and Uv rays are less when compared . REFERENCES Assumus, A. (1995). History of rays. Early History of X-rays, 1-13. Linton, W. (1995). Medical Application of X-rays. Beeson, Steven; Mayer, James W. Discoveries beyond the visible. Patterns of light: chasing the spectrum from Aristotle to LEDs. New York: Springer. p. 14 Matsumu, Y.; Ananthaswamy, H. N. (2004). Toxic effects of ultraviolet radiation on the skin. Toxicology and Applied Pharmacology 195 (3): 298–308 Read More