When the thickness of the film is an odd multiple of one quarter-wavelength of the light on it, the reflected waves from both surfaces interfere to cancel each other. Since the wave cannot be reflected, it is transmitted instead. When the thickness is a multiple of a half-wavelength of the light, thus when white light, which consists of a range of wavelengths, is incident on the film, certain wavelengths are intensified while others are attenuated. Thin-film interference explains the colors seen in light reflected from soap bubbles. It is the mechanism behind the action of antireflection coatings used on glasses, studying the light reflected or transmitted by a thin film can reveal information about the thickness of the film or the effective refractive index of the film medium. Thin films have many applications including anti-reflection coatings, mirrors. A thin film is a layer of material thickness in the sub-nanometer to micron range. As light strikes the surface of a film it is transmitted or reflected at the upper surface.
Light that is transmitted reaches the surface and may once again be transmitted or reflected. The Fresnel equations provide a description of how much of the light will be transmitted or reflected at an interface. The light reflected from the upper and lower surfaces will interfere, the degree of constructive or destructive interference between the two light waves depends on the difference in their phase. This difference in turn depends on the thickness of the layer, the refractive index of the film. Additionally, a shift of 180° or π radians may be introduced upon reflection at a boundary depending on the refractive indices of the materials on either side of the boundary. This phase shift occurs if the index of the medium the light is travelling through is less than the refractive index of the material it is striking. In other words, if n 1 < n 2 and the light is travelling from material 1 to material 2, the pattern of light that results from this interference can appear either as light and dark bands or as colorful bands depending upon the source of the incident light.
Consider light incident on a film and reflected by both the upper and lower boundaries. The optical path difference of the light must be calculated in order to determine the condition for interference. 2 n 2 d cos = m λ This condition may change after considering possible phase shifts occur upon reflection
The peafowl include three species of birds in the genera Pavo and Afropavo of the Phasianidae family, the pheasants and their allies. There are two Asiatic species and one African species, male peafowl are known for their piercing call and their extravagant plumage. The latter is especially prominent in the Asiatic species, who have a tail or train of covert feathers which they display as part of a courtship ritual. The term peacock is properly reserved for the male, the female is known as a peahen, the functions of the elaborate iridescent coloration and large train of peacocks have been the subject of extensive scientific debate. Charles Darwin suggested they served to attract females, and the features of the males had evolved by sexual selection. The Indian peacock has iridescent blue and green plumage, the peacock tail, known as a train, consists not of tail quill feathers, but highly elongated upper tail coverts. These feathers are marked with eyespots, best seen when a peacock fans his tail, both sexes of all species have a crest atop the head.
The Indian peahen has a mixture of grey, brown. The female displays her plumage to ward off female competition or signal danger to her young, the green peafowl differs from the Indian peafowl in that the male has green and gold plumage with black wings with a sheen of blue. Unlike the Indian peafowl, the green peahen is similar to the male, only having shorter upper tail coverts, a more coppery neck, the Congo peacock male does not display his covert feathers, but uses his actual tail feathers during courtship displays. These feathers are shorter than those of the Indian and green species. Females of the Indian and African species are dull grey and/or brown, chicks of both sexes in all the species are cryptically coloured. They vary between yellow and tawny, usually with patches of brown or light tan and dirty white ivory. Occasionally, peafowl appear with white plumage and this can result in the complete lack of coloration of their plumage, while preserving normal eye colour. By contrast, true albino peafowl have a lack of melanin.
Leucistic peachicks are born yellow and become white as they mature. As with many birds, vibrant iridescent plumage colours are not primarily pigments, optical interference Bragg reflections based on regular, periodic nanostructures of the barbules of the feathers produce the peacocks colours. Slight changes to the spacing of these result in different colours
It was a part of the religion in ancient Greece. Greek mythology is explicitly embodied in a collection of narratives. Greek myth attempts to explain the origins of the world, and details the lives and adventures of a variety of gods, heroes, heroines. These accounts initially were disseminated in a tradition, today the Greek myths are known primarily from ancient Greek literature. The oldest known Greek literary sources, Homers epic poems Iliad and Odyssey, focus on the Trojan War, archaeological findings provide a principal source of detail about Greek mythology, with gods and heroes featured prominently in the decoration of many artifacts. Geometric designs on pottery of the eighth century BC depict scenes from the Trojan cycle as well as the adventures of Heracles, in the succeeding Archaic and Hellenistic periods and various other mythological scenes appear, supplementing the existing literary evidence. Greek mythology has had an influence on the culture, arts. Poets and artists from ancient times to the present have derived inspiration from Greek mythology and have discovered contemporary significance and relevance in the themes, Greek mythology is known today primarily from Greek literature and representations on visual media dating from the Geometric period from c.
Mythical narration plays an important role in every genre of Greek literature. Nevertheless, the only general mythographical handbook to survive from Greek antiquity was the Library of Pseudo-Apollodorus and this work attempts to reconcile the contradictory tales of the poets and provides a grand summary of traditional Greek mythology and heroic legends. Apollodorus of Athens lived from c, 180–125 BC and wrote on many of these topics. His writings may have formed the basis for the collection, however the Library discusses events that occurred long after his death, among the earliest literary sources are Homers two epic poems, the Iliad and the Odyssey. Other poets completed the cycle, but these and lesser poems now are lost almost entirely. Despite their traditional name, the Homeric Hymns have no connection with Homer. They are choral hymns from the part of the so-called Lyric age. Hesiods Works and Days, a poem about farming life, includes the myths of Prometheus, Pandora. The poet gives advice on the best way to succeed in a dangerous world, lyrical poets often took their subjects from myth, but their treatment became gradually less narrative and more allusive.
Greek lyric poets, including Pindar and Simonides, and bucolic poets such as Theocritus and Bion, myth was central to classical Athenian drama
Micrographia, or Some Phyſiological Deſcriptions of Minute Bodies Made by Magnifying Glasses. With Observations and Inquiries Thereupon. is a significant book by Robert Hooke about his observations through various lenses. It is particularly notable for being the first book to illustrate insects, plants etc. as seen through microscopes. Published in January 1665, the first major publication of the Royal Society, it became the first scientific best-seller and it is notable for coining the biological term cell. Hooke most famously describes a flys eye and a plant cell, known for its spectacular copperplate engravings of the miniature world, particularly its fold-out plates of insects, the text itself reinforces the tremendous power of the new microscope. The plates of insects fold out to be larger than the large folio itself, Hooke selected several objects of human origin, among these objects were the jagged edge of a honed razor and the point of a needle, seeming blunt under the microscope. His goal may well have been as a way to contrast the flawed products of mankind with the perfection of nature, gallery Published under the aegis of The Royal Society, the popularity of the book helped further the societys image and mission of being the UKs leading scientific organization.
Micrographias illustrations of the miniature world captured the imagination in a radically new way. Similarly his specimens required a deal of manipulation and preparation in order to make them visible through the microscope. Additionally, Hooke often enclosed the objects he presented within a round frame, micrographia, or, Some physiological descriptions of minute bodies made by magnifying glasses. London, J. Martyn and J. Allestry,1665
A rainbow is a meteorological phenomenon that is caused by reflection and dispersion of light in water droplets resulting in a spectrum of light appearing in the sky. It takes the form of a multicoloured arc, Rainbows caused by sunlight always appear in the section of sky directly opposite the sun. However, the observer sees only an arc formed by illuminated droplets above the ground. In a primary rainbow, the arc shows red on the outer part and this rainbow is caused by light being refracted when entering a droplet of water, reflected inside on the back of the droplet and refracted again when leaving it. In a double rainbow, an arc is seen outside the primary arc. A rainbow is not located at a distance from the observer. Thus, a rainbow is not an object and cannot be physically approached, indeed, it is impossible for an observer to see a rainbow from water droplets at any angle other than the customary one of 42 degrees from the direction opposite the light source. Even if an observer sees another observer who seems under or at the end of a rainbow, Rainbows span a continuous spectrum of colours.
Rainbows can be caused by many forms of airborne water and these include not only rain, but mist and airborne dew. Rainbows can be observed there are water drops in the air. Because of this, rainbows are seen in the western sky during the morning. The most spectacular rainbow displays happen when half the sky is dark with raining clouds. The result is a rainbow that contrasts with the darkened background. During such good visibility conditions, the larger but fainter secondary rainbow is often visible and it appears about 10° outside of the primary rainbow, with inverse order of colours. The rainbow effect is commonly seen near waterfalls or fountains. In addition, the effect can be created by dispersing water droplets into the air during a sunny day. Rarely, a moonbow, lunar rainbow or nighttime rainbow, can be seen on strongly moonlit nights, as human visual perception for colour is poor in low light, moonbows are often perceived to be white. It is difficult to photograph the complete semicircle of a rainbow in one frame, for a 35 mm camera, a wide-angle lens with a focal length of 19 mm or less would be required
In optics, a diffraction grating is an optical component with a periodic structure, which splits and diffracts light into several beams travelling in different directions. The emerging coloration is a form of structural coloration, the directions of these beams depend on the spacing of the grating and the wavelength of the light so that the grating acts as the dispersive element. Because of this, gratings are used in monochromators and spectrometers. For practical applications, gratings generally have ridges or rulings on their surface rather than dark lines, such gratings can be either transmissive or reflective. Gratings which modulate the phase rather than the amplitude of the incident light are produced, the principles of diffraction gratings were discovered by James Gregory, about a year after Newtons prism experiments, initially with items such as bird feathers. The first man-made diffraction grating was made around 1785 by Philadelphia inventor David Rittenhouse and this was similar to notable German physicist Joseph von Fraunhofers wire diffraction grating in 1821.
Diffraction can create rainbow colors when illuminated by a wide spectrum light source, a grating has parallel lines, while a CD has a spiral of finely-spaced data tracks. Diffraction colors appear when one looks at a point source through a translucent fine-pitch umbrella-fabric covering. Decorative patterned plastic films based on reflective grating patches are very inexpensive, the relationship between the grating spacing and the angles of the incident and diffracted beams of light is known as the grating equation. Gratings may be of the reflective or transmissive type, analogous to a mirror or lens, respectively. A grating has a mode, in which there is no diffraction. An idealised grating is considered here which is made up of a set of slits of spacing d, assuming a plane wave of monochromatic light of wavelength λ with normal incidence, each slit in the grating acts as a quasi point-source from which light propagates in all directions. After light interacts with the grating, the light is composed of the sum of interfering wave components emanating from each slit in the grating.
At any given point in space through which diffracted light may pass, when the path difference is λ, the phases will add together and maxima will occur. Thus, when light is incident on the grating, the diffracted light will have maxima at angles θm given by. It is straightforward to show if a plane wave is incident at any arbitrary angle θi. When solved for the diffracted angle maxima, the equation is, please note that these equations assume that both sides of the grating are in contact with the same medium. The light that corresponds to direct transmission is called the zero order, the other maxima occur at angles which are represented by non-zero integers m
Cloud iridescence is the occurrence of colors in a cloud similar to those seen in oil films on puddles, located in the general vicinity of the sun or moon. It is a common phenomenon, most often observed in altocumulus, lenticular clouds. The colors are usually pastel, but can be very vivid, when occurring near the sun, the effect can be difficult to spot as it is drowned in the suns glare. This may be overcome by blocking the sun with ones hand or hiding it behind a tree or building, other aids are dark glasses, or observing the sky reflected in a convex mirror or in a pool of water. The effect is similar to irisation, Iridescent clouds are a diffraction phenomenon caused by small water droplets or small ice crystals individually scattering light. Larger ice crystals do not produce iridescence, but can cause halos, if parts of clouds contain small water droplets or ice crystals of similar size, their cumulative effect is seen as colors. The cloud must be thin, so that most rays encounter only a single droplet.
Iridescence is therefore mostly seen at cloud edges or in semi-transparent clouds, polar stratospheric cloud Iridescent cloud gallery - Atmospheric Optics site On the Cause of Iridescence in Clouds - Scientific American Supplement
Hummingbirds are birds from the Americas that constitute the family Trochilidae. They are among the smallest of birds, most species measuring 7. 5–13 cm, the smallest extant bird species is a hummingbird, the 5-cm bee hummingbird weighing less than 2.5 g. They are known as hummingbirds because of the sound created by their beating wings which flap at high frequencies audible to humans. They hover in mid-air at rapid wing-flapping rates, typically around 50 times per second, hummingbirds have the highest metabolism of any homeothermic animal. To conserve energy when food is scarce, and nightly when not foraging, they go into torpor, a map of the hummingbird family tree—reconstructed from analysis of 284 of the worlds 338 known species—shows rapid diversification from 22 million years ago. Due to this exceptional evolutionary pattern, as many as 140 hummingbird species can coexist in a specific region, the hummingbird evolutionary tree shows ancestral hummingbirds splitting from insectivorous swifts and treeswifts about 42 million years ago, probably in Eurasia.
One key evolutionary factor appears to be an altered taste receptor that enabled hummingbirds to seek nectar, by 22 million years ago the ancestral species of current hummingbirds became established in South America, where environmental conditions stimulated further diversification. The Andes Mountains appear to be a rich environment for hummingbird evolution because diversification occurred simultaneously with mountain uplift over the past 10 million years. Hummingbirds remain in dynamic diversification inhabiting ecological regions across South America, North America, within the same geographic region, hummingbird clades co-evolved with nectar-bearing plant clades, affecting mechanisms of pollination. The same is true for the hummingbird, one of the morphologically most extreme species. Hummingbirds exhibit sexual size dimorphism according to Renschs rule, in males are smaller than females in small species. The extent of sexual size difference varies among clades of hummingbirds. For example, the Mellisugini clade exhibits a large size dimorphism, the Lophomithini clade displays very little size dimorphism and females are similar in size.
For males and females of the size, females will tend to have larger beaks. Males tend to be smaller than females, allowing conservation of energy to forage competitively, sexual selection will favor smaller male hummingbirds. Female hummingbirds tend to be larger, requiring energy, with longer beaks that allow for more effective reach into crevices of tall flowers for nectar. Thus females are better at foraging, acquiring flower nectar, directional selection will thus favor the larger hummingbirds in terms of acquiring food. Another evolutionary cause of this sexual dimorphism is that the selective forces from competition for nectar between the sexes of each species are what drive the sexual dimorphism
The birds-of-paradise are members of the family Paradisaeidae of the order Passeriformes. The majority of species are found in eastern Indonesia, Papua New Guinea, the family has 42 species in 15 genera. For the most part they are confined to dense rainforest habitat, the diet of all species is dominated by fruit and to a lesser extent arthropods. The birds-of-paradise have a variety of breeding systems, ranging from monogamy to lek-type polygamy, a number of species are threatened by hunting and habitat loss. For many years the birds-of-paradise were treated as being related to the bowerbirds. Today while both are treated as being part of the Australasian lineage Corvida, the two are now thought to be distantly related. The closest evolutionary relatives of the birds-of-paradise are the crow and jay family Corvidae, the monarch flycatchers Monarchidae, the second clade includes the parotias and the King of Saxony bird-of-paradise. The third clade provisionally contains a number of genera, the Drepanornis sicklebills, Semioptera and Lophorina, the fourth clade includes the Epimachus sicklebills and the astrapias.
The final clade includes the Cicinnurus and the Paradisaea birds-of-paradise, the exact limits of the family have been the subject of revision as well. The three species of satinbird were treated as a subfamily of the birds-of-paradise, Cnemophilinae, in spite of differences in the mouth, foot morphology and nesting habits they remained in the family until a 2000 study moved them to a separate family closer to the berrypeckers and longbills. The same study found that the Macgregors bird-of-paradise was actually a member of the large Australasian honeyeater family, in addition to these three species, a number of systematically enigmatic species and genera have been considered potential members of this family. The silktail of Fiji has been linked with the many times since its discovery. Recent molecular evidence now places the species with the fantails, hybrid birds-of-paradise may occur when individuals of different species, that look similar and have overlapping ranges, confuse each other for their own species and crossbreed.
Birds-of-paradise are closely related to the corvids, birds-of-paradise range in size from the king bird-of-paradise at 50 g and 15 cm to the curl-crested manucode at 44 cm and 430 g. The male black sicklebill, with its tail, is the longest species at 110 cm. In most species, the tails of the males are larger and longer than the female, the wings are rounded and in some species structurally modified on the males in order to make sound. There is considerable variation in the family with regard to bill shape, bills may be long and decurved, as in the sicklebills and riflebirds, or small and slim like the Astrapias. As with body size bill size varies between the sexes, although species where the females have larger bills than the male are more common, plumage variation between the sexes is closely related to breeding system
Parrots, known as psittacines /ˈsɪtəsaɪnz/, are birds of the roughly 393 species in 92 genera that make up the order Psittaciformes, found in most tropical and subtropical regions. The order is subdivided into three superfamilies, the Psittacoidea, the Cacatuoidea, and the Strigopoidea, Parrots have a generally pantropical distribution with several species inhabiting temperate regions in the Southern Hemisphere, as well. The greatest diversity of parrots is in South America and Australasia, characteristic features of parrots include a strong, curved bill, an upright stance, strong legs, and clawed zygodactyl feet. Many parrots are vividly coloured, and some are multi-coloured, most parrots exhibit little or no sexual dimorphism in the visual spectrum. They form the most variably sized bird order in terms of length, the most important components of most parrots diets are seeds, fruit and other plant material. A few species sometimes eat animals and carrion, while the lories and lorikeets are specialised for feeding on floral nectar, almost all parrots nest in tree hollows, and lay white eggs from which hatch altricial young.
Parrots, along with ravens, crows and magpies, are among the most intelligent birds, some parrots are intelligent and talk at the level of a four-to-five year old human. Measures taken to conserve the habitats of some high-profile charismatic species have protected many of the less charismatic species living in the same ecosystems. Psittaciform diversity in South America and Australasia suggests that the order may have evolved in Gondwana, molecular studies suggest that parrots evolved approximately 59 million years ago in Gondwana. The three major clades of Neotropical parrots originated about 50 Mya, the earliest parrots do not have the specialised crushing bills of modern species. If so, they probably had not evolved their morphological autapomorphies yet, the combined evidence supported the hypothesis of Psittaciformes being near passerines, i. e. the mostly land-living birds that emerged in close proximity to the K-Pg extinction. Europe is the origin of the first undeniable parrot fossils, which date from about 50 Mya, the climate there and was tropical, consistent with the Paleocene-Eocene thermal maximum.
Initially, a neoavian named Mopsitta tanta, uncovered in Denmarks Early Eocene Fur Formation and dated to 54 Mya, was assigned to the Psittaciformes, fossils assignable to Psittaciformes date from slightly in the Eocene, starting around 50 Mya. Several fairly complete skeletons of birds have been found in England. The fossil record—mainly from Europe—consists of bones clearly recognisable as belonging to parrots of modern type, at this point, however, is found the first unambiguous parrot fossil, an upper jaw that is indistinguishable from that of modern cockatoos. The Psittaciformes comprise three lineages, Strigopoidea and Cacatuoidea. Colourful feathers with high levels of psittacofulvin resist the feather-degrading bacterium Bacillus licheniformis better than white ones, lorikeets were previously regarded as a third family, but are now considered a tribe within the subfamily Lorinae, family Cacatuoidea. The two other tribes in the subfamily are the closely related fig parrots and budgerigar, the order Psittaciformes consists of roughly 393 species belonging to 92 genera
Amplitude modulation is a modulation technique used in electronic communication, most commonly for transmitting information via a radio carrier wave. In amplitude modulation, the amplitude of the wave is varied in proportion to the waveform being transmitted. That waveform may, for instance, correspond to the sounds to be reproduced by a loudspeaker and this technique contrasts with frequency modulation, in which the frequency of the carrier signal is varied, and phase modulation, in which its phase is varied. AM was the earliest modulation method used to transmit voice by radio and it was developed during the first two decades of the 20th century beginning with Roberto Landell De Moura and Reginald Fessendens radiotelephone experiments in 1900. It remains in use today in many forms of communication, for example it is used in two way radios, VHF aircraft radio, Citizens Band Radio, and in computer modems. AM is often used to refer to mediumwave AM radio broadcasting, when it reaches its destination, the information signal is extracted from the modulated carrier by demodulation.
In amplitude modulation, the amplitude or strength of the oscillations is what is varied. For example, in AM radio communication, a continuous wave signal has its amplitude modulated by an audio waveform before transmission. The audio waveform modifies the amplitude of the wave and determines the envelope of the waveform. In the frequency domain, amplitude modulation produces a signal with power concentrated at the carrier frequency, each sideband is equal in bandwidth to that of the modulating signal, and is a mirror image of the other. Standard AM is thus sometimes called double-sideband amplitude modulation to distinguish it more sophisticated modulation methods based on AM. One disadvantage of all amplitude modulation techniques is that the receiver amplifies and detects noise, increasing the received signal to noise ratio, say, by a factor of 10, thus would require increasing the transmitter power by a factor of 10. For this reason AM broadcast is not favored for music and high fidelity broadcasting, another disadvantage of AM is that it is inefficient in power usage, at least two-thirds of the power is concentrated in the carrier signal.
The carrier signal contains none of the information being transmitted. However its presence provides a means of demodulation using envelope detection, providing a frequency. The receiver may regenerate a copy of the frequency from a greatly reduced pilot carrier to use in the demodulation process. Even with the carrier totally eliminated in double-sideband suppressed-carrier transmission, carrier regeneration is possible using a Costas phase-locked loop and this doesnt work however for single-sideband suppressed-carrier transmission, leading to the characteristic Donald Duck sound from such receivers when slightly detuned. Single sideband is used widely in amateur radio and other voice communications both due to its power efficiency and bandwidth efficiency
A soap bubble is an extremely thin film of soapy water enclosing air that forms a hollow sphere with an iridescent surface. Soap bubbles usually last for only a few seconds before bursting and they are often used for childrens enjoyment, but they are used in artistic performances. Assembling several bubbles results in a foam, when light shines onto a bubble it appears to change colour. Depending on the thickness of the film, different colours interfere constructively and destructively, Soap bubbles are physical examples of the complex mathematical problem of minimal surface. They will assume the shape of least surface area possible containing a given volume, a true minimal surface is more properly illustrated by a soap film, which has equal pressure on inside as outside, hence is a surface with zero mean curvature. A soap bubble is a soap film, due to the difference in outside and inside pressure. This has been dubbed the double bubble conjecture, due to these qualities soap bubbles films have been used with practical problem solving application.
A famous example is his West German Pavilion at Expo 67 in Montreal, when two bubbles merge, they adopt a shape which makes the sum of their surface areas as small as possible, compatible with the volume of air each bubble encloses. If the bubbles are of size, their common wall is flat. If they arent the same size, their common wall bulges into the bubble, since the smaller one has a higher internal pressure than the larger one. At a point where three or more bubbles meet, they sort themselves out so only three bubble walls meet along a line. Since the surface tension is the same in each of the three surfaces, the three angles between them must be equal to 120°, only four bubble walls can meet at a point, with the lines where triplets of bubble walls meet separated by cos−1 ≈109. 47°. All these rules, known as Plateaus laws, determine how a foam is built from bubbles, the longevity of a soap bubble is limited by the ease of rupture of the very thin layer of water which constitutes its surface, namely a micrometer-thick soap film.
It is thus sensitive to, Drainage within the soap film and this can be slowed down by increasing the water viscosity, for instance by adding glycerol. Still, there is a height limit, which is the capillary length, very high for soap bubbles. In principle, there is no limit in the length it can reach, This can be slowed down by blowing bubbles in a wet atmosphere, or by adding some sugar to the water. Dirt and fat, When the bubble touches the ground, a wall, or our skin and this can be prevented by wetting these surfaces with water. When a soap bubble is in contact with a solid or a liquid surface wetting is observed, on a solid surface, the contact angle of the bubble depends on the surface energy of the solid