Term 1 Self-directed and Independent Research Learning

History of Magnesium

Magnesium was discovered by Sir Humphrey Davy at 1755 in England. Origin of name: from the Greek word "Magnesia", a district of Thessaly.

In 1618, a farmer at Epsom in England attempted to give his cows water from a well. They refused to drink the water. However, the farmer noticed that the water seemed to heal scratches and rashes. The fame of this water, later known as Epsom salts spread. Eventually they were recognised to be magnesium sulphate, MgSO4.

Joseph Black recognized magnesium as an element in 1755. It was isolated by Sir Humphry Davy (1778-1829) in 1808 almost 200 years after its discovery. He electrolysised mixture of magnesia (magnesium oxide, MgO) and mercuric oxide (HgO). Davy's first suggestion for a name was magnesium but the name magnesium is now used.

Michael Faraday produced magnesium metal by electrolysis of fused anhydrous magnesium chloride in 1833. The commercial production of magnesium by electrolysis is credited to Robert Bunsen who in 1852 made a small laboratory cell for the electrolysis of fused magnesium chloride. Bunsen’s modificated cell was used in ‘ The Aluminium and Magnesium Fabrik’ in Hemelingen in Germany for the first commercial magnesium production.

In 1896, this process was further developed by Griesheim-Elektron Chemische Fabrik, a scientist, who transferred the process to its Bitterfield Works and became the only magnesium producing facility in the world until 1916 and then became part of I.G. Farbenindustrie.

Lloyd Montgomery Pidgeon was an Canadian scientist who was head at the Department of Metallurgy at the university of Toronto. He developed the magnesium process that bears his name and also new electrolytic processes.

The name magnesium comes from Magnesia, a district of Thessaly/Greece were it was first found and to this present day a lot of magnesium ore is present in the area.

Source: https://www.webelements.com/magnesium/history.html

            http://www.magnesiumsquare.com/index.php?option=com_content&view=article&id=13&Itemid=31

Science of Photography

A photographic lens is usually composed of several lens elements, which combine to reduce the effects of chromatic aberration, coma, spherical aberration, and other aberrations.

Using a smaller aperture can reduce most, but not all aberrations. They can also be reduced dramatically by using an aspheric element, but these are more complex to grind than spherical or cylindrical lenses. However, with modern manufacturing techniques the extra cost of manufacturing aspherical lenses is decreasing, and small aspherical lenses can now be made by molding, allowing their use in inexpensive consumer cameras. Fresnel lenses are not used in cameras even though they are extremely light and cheap, because they produce poor image quality. The recently developed Fibre-coupled monocentric lens consists of spheres constructed of concentric hemispherical shells of different glasses tied to the focal plane by bundles of optical fibers. Monocentric lenses are also not used in cameras because the technology was just debuted in October 2013 at the Frontiers in Optics Conference in Orlando, Florida.

All lens design is a compromise between numerous factors, not excluding cost. Zoom lenses involve additional compromises and therefore normally do not match the performance of prime lenses.

When a camera lens is focused to project an object some distance away onto the film or detector, the objects that are closer in distance, relative to the distant object, are also approximately in focus. The range of distances that are nearly in focus is called the depth of field. Depth of field generally increases with decreasing aperture diameter. The unfocused blur outside the depth of field is sometimes used for artistic effect in photography.

In an SLR camera, you see the actual real image that the film will see. If you take the lens off of an SLR camera and look inside, you'll see how this works. The camera has a slanted mirror positioned between the shutter and the lens, with a piece of translucent glass and a prism positioned above it. This configuration works like a periscope -- the real image bounces off the lower mirror on to the translucent glass, which serves as a projection screen.

A lens with a rounder shape will have a more acute bending angle. Basically, curving the lens out increases the distance between different points on the lens. This increases the amount of time that one part of the light wave is moving faster than another part, so the light makes a sharper turn.

Increasing the bending angle has an obvious effect. Light beams from a particular point will converge at a point closer to the lens. In a lens with a flatter shape, light beams will not turn as sharply. Consequently, the light beams will converge farther away from the lens. To put it another way, the focused real image forms farther away from the lens when the lens has a flatter surface.

Increasing the distance between the lens and the real image actually increases the total size of the real image. To put it simply, the light beams keep spreading apart as they travel toward the screen.

As the distance between the lens and the real image increases, the light beams spread out more, forming a larger real image. But the size of the film stays constant. When you attach a very flat lens, it projects a large real image but the film is only exposed to the middle part of it. Basically, the lens zeroes in on the middle of the frame, magnifying a small section of the scene in front of you. A rounder lens produces a smaller real image, so the film surface sees a much wider area of the scene (at reduced magnification).

The magnification power of a lens is described by its focal length. In cameras, the focal length is defined as the distance between the lens and the real image of an object in the far distance (the moon for example). A higher focal length number indicates a greater image magnification.

Different lenses are suited to different situations. If you're taking a picture of a mountain range, you might want to use a telephoto lens, a lens with an especially long focal length. This lens lets you zero in on specific elements in the distance, so you can create tighter compositions. If you're taking a close-up portrait, you might use a wide-angle lens. This lens has a much shorter focal length, so it shrinks the scene in front of you. The entire face is exposed to the film even if the subject is only a foot away from the camera. A standard 50 mm camera lens doesn't significantly magnify or shrink the image, making it ideal for shooting objects that aren't especially close or far away.

                                

Source: http://en.wikipedia.org/wiki/Science_of_photography

            http://www.popphoto.com/news/2012/10/learn-science-behind-photography-courtesy-stanford

            http://electronics.howstuffworks.com/camera.htm
            https://www.youtube.com/watch?v=F8T94sdiNjc

Vision Correction

Farsightedness

Farsightedness or hyperopia is the inability of the eye to focus on nearby objects. The farsighted eye has no difficulty viewing distant objects. But the ability to view nearby objects requires a different lens shape - a shape that the farsighted eye is unable to assume. Subsequently, the farsighted eye is unable to focus on nearby objects. The problem most frequently arises during latter stages in life. Ageing leads to the result that the lens of the eye can no longer assume the high curvature that is required to view nearby objects. The lens' power to refract light has diminished and the images of nearby objects are focused at a location behind the retina. On the retinal surface, where the light-detecting nerve cells are located, the image is not focused. These nerve cells thus detect a blurry image of nearby objects.

The cure for the farsighted eye centers around assisting the lens in refracting the light. Since the lens can no longer assume the convex and highly curved shape that is required to view nearby objects, it needs some help. Thus, the farsighted eye is assisted by the use of a converging lens. This converging lens will refract light before it enters the eye and subsequently decreases the image distance. By beginning the refraction process prior to light reaching the eye, the image of nearby objects is once again focused upon the retinal surface.

Nearsightedness

Nearsightedness or myopia is the inability of the eye to focus on distant objects. The nearsighted eye has no difficulty viewing nearby objects. But the ability to view distant objects requires that the light be refracted less. Nearsightedness will occur if the light from distant objects is refracted more than is necessary. The problem is most common as a youth, and is usually the result of a bulging cornea or an elongated eyeball. It causes the images of distant objects to form at locations in front of the retina. If the eyeball is elongated in the horizontal direction, then the retina is placed at a further distance from the cornea-lens system. Subsequently the images of distant objects form in front of the retina. On the retinal surface, where the light-detecting nerve cells are located, the image is not focused. These nerve cells thus detect a blurry image of distant objects.

The cure for the nearsighted eye is to equip it with a diverging lens. Since the nature of the problem of nearsightedness is that the light is focused in front of the retina, a diverging lens will serve to diverge light before it reaches the eye. This light will then be converged by the cornea and lens to produce an image on the retina.

Source: http://www.physicsclassroom.com/class/refrn/Lesson-6/Farsightedness-and-its-Correction

            http://www.physicsclassroom.com/class/refrn/Lesson-6/Nearsightedness-and-its-Correction

            https://www.youtube.com/watch?v=N16IT8Nxj6A