Scattering of Light

Scattering of Light Callum Lim Contents 1. Rayleigh scattering 1.1 Mid-day 1.2 Sunrise and sunset 1.3 Night-time 2. Mie scattering 2.1 Clouds 3. Pollution 3.1 Light pollution 3.2 Haze 4. Personal reflections 5. Conclusion 6. Bibliography 1. Rayleigh scattering When a beam of light travels through particles which are smaller than its wavelength, it is possible these particles scatter the light beam in a process known as Rayleigh scattering. This process is visible everyday whenever sunlight is scattered by the Earth’s atmosphere. As sunlight is composed of different visible wavelengths of light – mainly Red, Orange, Yellow, Green, Blue, Indigo and Violet; ROYGBIV – not all sunlight has the same probability of being scattered. It is possible to determine the amount of Rayleigh scattering that the different visible wavelengths in sunlight experience by calculating the intensity of the individual scattered wavelengths. The intensity of light scattered by small particles (I) depends on the intensity (I0) and wavelength (ÃŽ ») of the light source, the distance of the light source from the particle (R), the scattering angle (ÃŽ ¸), the refractive index of the particle (n), and the diameter of the particle (d). The relationship between these variables is illustrated in the following equation: (Seinfeld Pandis , 2006) 1.1 Mid-day When the Sun is directly overhead, all the wavelengths of light originating from it travel the same distance from the Sun and through our atmosphere and are scattered by the same medium (nitrogen and oxygen molecules). Hence, I0, R, ÃŽ ¸, n and d remain constant and the above equation can be simplified into: With this equation, it can be seen that the intensity of scattered light is inversely proportional to the fourth power of a light’s wavelength and that the shorter a light’s wavelength, the more intensely visible it is. Hence, as GBIV light (400nm to 500nm) have shorter wavelengths compared to ROY light (570nm to 700nm), GBIV light is more intensely visible to us. Due to the shorter wavelengths of GBIV light, they also have higher chances of encountering atmospheric molecules than the ROY light and getting scattered by it, as shown in the figure below. Although scattered light continues travelling in a random direction, a greater proportion of GBIV than ROY light reaches our eyes because GBIV wavelengths are shorter and more easily scattered. However, as our eyes detect the blue component in GBIV light that has been scattered the easiest (Leong, 2006), we see the mid-day sky as blue in colour. 1.2 Sunrise and sunset At sunrise and sunset, sunlight has to travel through a longer distance through the atmosphere than at mid-day before it is visible. As a result, sunlight encounters more atmospheric molecules during these times which results in more scattering of light. Hence, with this increased distance, even the higher wavelengths (ROY) are scattered, and this colours the sky reddish-orange. However, it is only at the horizons that the sky looks reddish-orange because the multiple rays of sunlight travel through different distances in the atmosphere due to refraction. As seen in the figure above, sunlight ray A penetrates the atmosphere very minimally and experiences very little refraction. As a result, it travels the shortest distance through the atmosphere and gets very little scattering. Thus, only the violet and indigo wavelengths are scattered. Sunlight ray B enters more deeply into atmosphere than A and gets refracted more. Hence, it has to travel a longer distance through the atmosphere which scatters most of BIV wavelengths. Before it leaves the atmosphere, however, the remaining wavelengths are scattered which results in a portion of the sky looking yellow. Sunlight ray C penetrates deepest into the atmosphere and experiences the most refraction. As it travels the longest distance of the three rays, its higher red and orange wavelengths are also scattered. This gives a portion of the sky its reddish-orange colour. Hence, this is why only the horizons are coloured reddish-orange while the rest of the sky remains blue during sunrise and sunset. 1.3 Night-time Sunlight reflected off the moon undergoes Rayleigh scattering as well, although its effects are not as visible. As mentioned earlier, the intensity of the light source (I0) and the distance of the light source from the particle (R) also affects the how intensely visible the scattered light is. Although the Moon is much closer to the Earth than the Sun, the light we get from it is much less intense than that from the Sun, thus reducing the intensity of scattered light. 2. Mie scattering Aside from Rayleigh scattering, another type of scattering, in the form of Mie scattering, exists. This occurs when sunlight encounters molecules which are comparable in size to its composite wavelengths. As a result, all visible wavelengths in sunlight are almost scattered equally. 2.1 Clouds On a daily basis, Mie scattering is observable when we look at clouds. As water vapour in clouds tend to be 20 micrometres in diameter (University of Illinois, 2010), all visible wavelengths in sunlight are scattered by clouds equally, thus giving clouds their white appearance. Bigger clouds or rain clouds usually look darker because they are bigger and contain more water vapour molecules. Thus, as these clouds scatter most of the sunlight that pass through them, very little sunlight exits through the bottoms of these clouds. Besides appearing white or grey, clouds can also appear reddish at sunrise or sunset. This is attributed to both Mie and Rayleigh scattering. At these times, sunlight travels a longer distance through the atmosphere and most of the shorter GBIV wavelengths are scattered just as sunlight enters the atmosphere. Hence, the further sunlight travels through the atmosphere, the greater the proportion of longer ROY wavelengths that remain. Thus, it is mainly the ROY wavelengths that are able to reach and get scattered by the clouds; and this causes clouds to appear reddish. Mie scattering is also observable on nights when moonlight is scattered by clouds in the sky and results in clouds appearing white. 3. Pollution 3.1 Light pollution On certain late nights, it is also possible to observe red clouds in the sky even when there is no source of light in the atmosphere. This phenomenon is a result of denser clouds scattering light from the city back down onto Earth. As Singapore is mostly lit up by yellow or orange light from streetlights, a greater proportion of longer wavelengths are scattered by the clouds thus making the clouds look red. However, if the clouds do not contain enough water vapour molecules and hence, are not large or dense enough, less city light is scattered. Thus, the redness visible in these clouds is not as pronounced and this is why red clouds are not always visible at night. Besides Mie scattering, city light also undergoes Rayleigh scattering at night, although its effect is not as obvious as scattered sunlight. While city light is mostly emitted in longer wavelengths and do not experience much Rayleigh scattering, its shorter wavelengths are greatly scattered by atmospheric particles as it travels through the atmosphere. Consequently, the shorter wavelengths of light scattered through Rayleigh scattering, together with the light scattered by clouds, increase the ambient brightness of Singapore’s night sky and inadvertently blocks out dimmer interstellar light that would otherwise be visible. Thus, this is why it is quite difficult to see deep-space objects in most of Singapore with the naked-eye. 3.2 Haze When dust and smoke particles from haze are present in the atmosphere, it becomes denser and causes light to undergo both Rayleigh and Mie scattering. This is because these particles typically range from 2.5 micrometres to 10 micrometres in diameter (Association of South East Asian Nations, 2014) and hence, are larger than visible light wavelengths. Thus, when the PSI is in the moderate range or worse, it is possible to see that all light appears muted and dull. At night, haze also causes Mie scattering of city light not only in clouds but throughout the sky. This results in significant portions night sky taking on a reddish glow. 4. Personal reflections Through this project, I now have a better understanding of why the sky and clouds appear to change in colour over time as well as why it is relatively difficult to observe the cosmos in a brightly lit city at night. The latter was evident when our group spent a day at Changi beach to photograph the colours changes in the sky. Just as we were leaving the seaside after twilight, we noticed that were more stars were visible in the night sky than what can normally be seen in the brighter urban areas of Singapore. Unfortunately, we did not have a good enough camera that was able to photograph the stars in the night sky then. One of the interesting things I have learnt from this project is also why the sky looks red on hazy nights, even when there is no light from the Sun or Moon. This is primarily due to light pollution that is scattered back down to Earth by smoke and dust particles in the atmosphere. Similarly, denser clouds at night appear red due to light pollution being scattered back down by water vapour within them. It is also because of light pollution that the adage â€Å"red sky at night, sailor’s delight† no longer holds true all the time, especially in cities that are brightly lit up at night. This is because the red sky at night might not be due to a high-pressure system in the west bringing calm weather, but due to manmade causes mentioned above (Teitel, 2012). This manmade phenomenon also has an implication on our circadian rhythms that act as our natural body clocks. Brighter skies at night could confuse our brains into thinking that it is daytime (and not time to sleep), thus disrupting our sleeping patterns and leaving us feeling jet-lagged. In the near future, the night sky might become even brighter as gas-discharge lights are replaced by light-emitting diode (LED) lights, which emit a greater concentration of shorter wavelengths (Teitel, 2012). Our circadian rhythms might be even more negatively affected by this increase in blue light, as they are especially sensitive to shorter wavelengths. A potential solution to mitigate this problem is to use warm white lights that emit minimal blue wavelengths. Additionally, understanding how light is affected by minute particles has also allowed humankind to apply these principles in real-life, such as in optical fibres. In optical fibres, light is used to transmit signals through cables made of transparent silica fibres. Since the silica molecules in these fibres are much smaller than the wavelength of visible light (Yao, 2010), Rayleigh scattering occurs within these cables and causes light to be scattered in a random direction instead of travelling through the cable. This is detrimental to signal strength. Hence, as Rayleigh scattering is extremely dependant on a light’s wavelength and short wavelengths of light scatter the most, optical fibres usually transmit signals in longer light wavelengths to minimise scattering. 5. Conclusion One of the most observable phenomena by the naked eye, the sky is often photographed at sunrise or sunset for its picturesque clouds. Besides just appreciating the beauty of these occurrences, I now understand the science behind them as well. Additionally, I also now know why the sky or clouds are red on certain nights even when there is no light from the Sun or the Moon. Besides the theoretical principles and atmospheric observations, scattering of light also has practical applications in real-life. In times before satellite imaging existed to forecast weather, people referred to colours in the night sky to determine if there would be good weather the next day. Today, knowledge of light scattering is also useful in deciding what wavelengths of light should be used when transmitting signals through optical fibres. In addition, understanding Rayleigh and Mie scattering also allows us to minimise to impact that bright skies might have on our natural body clocks. Thus, the study of light scattering not only allows us to better appreciate our atmosphere, but also apply these concepts in real-life. (1949 words; excluding citations) - End - 6. Bibliography Association of South East Asian Nations. (2014). Information on Fire and Haze. Retrieved 07 March, 2014, from ASEAN Haze Action Online: http://haze.asean.org/?page_id=249 Leong, J. (2006). Number of Colors Distinguishable by the Human Eye. (G. Elert, Editor) Retrieved 26 March, 2014, from The Physics Factbook: http://hypertextbook.com/facts/2006/JenniferLeong.shtml Nave, C. R. (2012). Blue Sky. Retrieved 17 March, 2014, from hyperphysics: http://hyperphysics.phy-astr.gsu.edu/hbase/atmos/blusky.html#c4 Seinfeld, J. H., Pandis , S. N. (2006). Atmospheric Chemistry and Physics: From Air Pollution to Climate Change, 2nd Edition. New Jersey: John Wiley and Sons. Siegel, E. (08 September, 2009). Red sky at night†¦ but why? Retrieved 05 March, 2014, from scienceblogs.com: http://scienceblogs.com/startswithabang/2009/09/08/red-sky-at-night-but-why/ Teitel, A. S. (23 August, 2012). Why Is the Night Sky Turning Red? Retrieved 28 February, 2014, from discovermagazine.com: http://blogs.discovermagazine.com/crux/2012/08/23/why-is-the-night-sky-turning-red/ University of Illinois. (2010). Scattering of Light. Retrieved 29 March, 2014, from WW2010: http://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/opt/mch/sct.rxml Yao, C. (20 September, 2010). Optical Fiber Loss and Attenuation. Retrieved 17 March, 2014, from Fibre Optics For Sale Co.: http://www.fiberoptics4sale.com/wordpress/optical-fiber-loss-and-attenuation/ GEK1520/PC1322 | Understanding the UniversePage 1 of 13

Creatine Monohydrate Supplementation :: Chemicals Anatomy Papers

Creatine Monohydrate Supplementation Creatine is a metabolite that is produced naturally by the human body. It is found mainly in the red muscle tissue, but it is also present in the heart and brain. Normally, creatine is acquired through regular dietary intake of products such as meat and fish, which are high in protein. However, when dietary intake is low creatine can be produced from natural amino acids such as glycine, arginine, and methionine in the liver, kidneys, and pancreas. Creatine monohydrate is the synthetic form of creatine (http://creatine-info.com/ - Information on Creatine Monohydrate). How does creatine work? What is its purpose? Creatine functions to increase the availability of cellular ATP, adenosine triphosphate. Muscular contractions take place off the presence of ATP and the how quickly it can be regenerated; therefore, an increase in creatine levels is thought to increase the force of muscle contractions (http://www.creatinefacts.com/creatine_monohydrate1.htm). Creatine works by acting on mechanisms of ATP by donating a phosphate ion to increase the availability of ATP. Thus, creatine claims to enhance physical performance by increasing energy and therefore, delaying or minimizing fatigue and adding to the amount of time spent training or working out (http://angelfire.com/co/Creatine/index.html and http://creatine-info.com/ - Information on Creatine Monohydrate). How much creatine should be taken? Currently there are no set dosage levels for creatine monohydrate because each person has a maximum level of creatine that cannot be exceeded; therefore, the key to creatine is to benefit from the lowest dosage possible. The most popular dosage regiment has two phases: the loading phase consists of loading the body with creatine to get the levels up. In this phase, 1 heaping teaspoon dose of approximately 5grams is recommended four times daily for one to five days. This is followed by the maintenance phase, which sustains the desired high levels of creatine in the body. The dosage is lowered to 1 teaspoon one to three times a day. The intake of creatine causes the muscle cells to volumize. Basically becoming very hydrated. However, other methods suggest that the loading phase is unnecessary (http://nutrasense.com/nutrasense/creatmon.htm - crdosage). It is also suggested that the most efficient way to maximize low dosages of creatine is to follow the dosage regiment in a cyclical fash ion. If creatine levels are allowed to subside and then one takes the supplement, greater results will be seen. In addition, more substantial improvements are likely to be seen in those with a restricted meat diet or those who are vegetarians (http://bodytrends.

Female and Camille Paglia Men

In the article Rape: A Bigger Danger than Feminists Know by Camille Paglia talks about how rape cannot be tolerated in a society and how feminism has put young women in danger by hiding the truth about sex from them. Although rape has been a problem for women for a long time, there was a time where the penalty for rape was death. However in the article Rape: A Bigger Danger than Feminist Know by Camille Paglia states â€Å"In our cities, on our campuses far from home, young women are vulnerable and defenseless†. Camille Paglia insists that feminism states that both sexes are equal nd tells women they can act, and dress any way they want. However Camille Paglia argues â€Å"No, they can’t and women will always be in sexual danger† (Camille Paglia, pg 40). As we will all know there are sexual differences that are based in biology, but according to academic feminism men and women are equal. Although Camille Paglia states that academic feminism is lost in a fog of so cial constructionism. She believes that college man are their hormonal peak and that a drunk girl at a part with them is setting herself for failure and will possibly be raped.According to Camille Paglia men and women are different because for example one of Camille Paglia make students recently slept overnight at a Great Pyramid in Egypt. The student described the moon, and sand, etc. Camille Paglia points out that because she is a woman, she would never get to experience that because it is to dangerous. Camille Paglia can possibly get robed, raped, murdered, and many other possible horrible things. Camille Paglia goes on to talk about how sexual desire and arousal cannot be fully translated into verbal terms.She believed that sometimes men and women tend to misunderstand each other. For example sometimes when a male and a female are alone and they kiss, the female might just want to kiss and the male may misunderstand that thinking that she wants to have sex. These types of situat ion sometimes lead to rape unfortunately. According to Camille Paglia rape is a big danger and woman need to know the precautions the can take to be safer. Camille Paglia makes it clear for woman not to blow off a vulgar remark directed towards them.Camille Paglia stated that if a male student makes a vulgar remark about a female students breast, that the female student should deal with it on the spot Camille Paglia states to respond with the situation by saying â€Å"Shut up, you jerk! † She believes this is the best way to deal with it instead of running to your mom and dad or some campus grievance committee. Camille Paglia believes that female students that stick up for themselves are the students that are harassed less often. Currently there are many rapes that happen all over the world, however according o Camille Paglia there are two solutions. Camille Paglia claims that female self- awareness and self-control. Basically for example a woman’s number-one line of d efense against rape is herself. If females educate themselves to help avoid, bad situations leading to rape, this will in turn reduce the percentage of rapes. She believes reporting rapes to College Committees would do a woman injustice. Camille Paglia explains that woman should report their rapes to the police instead of College committees who are not equipped or trained

Classroom Video Observations Essay - 1764 Words

Virtual Classroom Observations Video 1-6 Dr. Susan Stanley EDUC 656: Teaching Content Area Reading Liberty University By: Vanna Mata November 22, 2015 Video 1: Mark Diacopoulos In this video, Mr. Diacopoulos was teaching his class about the formation of the U.S. Constitution. He talked about the two sides of the politics; Federalists and the Anti-Federalists (Democratic Republicans). There were a couple of things that stood out for me in this video. First, it was his accent when he spoke. It was a little bit hard to understand. I also like that he had the Constitution posted on his walls. This allows the students to actual see what it is they are learning about. Another thing that stood out for me was how he allows the students†¦show more content†¦She decided that in allowing her 6th grade math class to work the school’s supply store would allow the students to apply real life situation to what they are studying in class. The students are responsible for opening the store, operating cash box, and closing the store. In what they learn in class, they applied to the store. In this particular unit they are working on sales tax and percentage. I think it is a great idea that what she is doing. In allowing the students to applied what they learn in class to a real life; makes it more interesting. Students are often wondering why they are learning something that they might not need later on. When she did this project, it gave the students the incentive to learn. If I have the opportunity, I would definitely have my students applied what they learn in the classroom to their own personal life. Only a glimpse into her day but from what I saw, it was all positive. The students are learning how to work well together without adult supervision. They are learning responsibilities and taking care of themselves. 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