Chhattisgarh State Exams

Before the introduction of plastics, iron was one of the most multipurpose materials, used to make almost everything. However, the only pure iron on Earth fell from space as meteorites, and that is far too rare to rely on. Most iron has been pushed up to the Earth's crust by activity in the planet's core, but this has reacted with many other elements, resulting in iron ore, rather than pure elemental iron. The process of separating iron from ore is called smelting: The ore is heated to a temperature at which it becomes a liquid, and then the metal is separated from the waste. Charcoal is one of the few materials that burns hot enough to melt iron. In Britain the iron industry originally moved around the country, burning forests and then moving on, but by the seventeenth century the industry was running out of trees and wood was becoming more...

Willem J. Kolff (b. 1911), a doctor working in occupied Holland during World War II, cobbled together the first kidney dialysis (hemodialysis) machine. When kidneys are not functioning correctly, waste products accumulate in the blood, and can be fatal. Kolff was aware of experiments showing that when two solutions of different chemical concentrations are separated by a permeable membrane an exchange of molecules takes place from the area of greater concentration to the area of lower concentration. Kolff's machine consisted of 66 feet (20 m) of cellophane tubing wound around a wooden drum that was suspended horizontally inside a tank filled with saline. As the drum was rotated by a motor, the patient's blood was forced through the tubing and its waste products crossed the membrane into the saline. A severe shortage of materials due to the war forced Kolff to improvise; he used cellophane that came from sausage casings. more...

On December 26, 1783, before a large public gathering at the base of the Montpellier Observatory in Paris, the French scientist and physicist Louis-Sebastien Lenormand jumped from the observatory's tower clinging to a 14-foot (4.2 m) parachute attached to an improvised wooden frame. Lenormand's leap of faith was the first ever documented use of a parachute and followed on from an earlier attempt at a slowed descent when he leaped from a tree holding on to nothing more than two modified parasols. Lenormand's inspiration likely came from the popular writings of a former French ambassador to China whose memoirs included an account of Chinese acrobats floating to earth using umbrellas. Chinese legends dating to 90 B.C.E. also tell of a group of prisoners who cheated death by leaping from a tower and slowing their descent with the aid of conical straw hats. Leonardo da Vinci sketched his famous pyramid- shaped more...

Plain old concrete—undeniably useful and popular though it may be—is really not as spectacular a material as you might at first think. Yes, It is good for making good, hard pavements and keeping fence- posts firmly in place in the ground, but if you are hoping to build « multistory car park out of it, or an overpass that runs above a busy motorway, you will quickly discover that concrete itself is not enough. In the 1860s, however, French gardener Joseph Monier (1823-1906) demonstrated the reinforced garden tubs he had made using ferroconcrete—a concrete and chicken-mesh combination that fellow Frenchman Joseph-Louis Lambot had pioneered. The garden tubs made their debut at the Paris Exposition of 1867, and Monier applied for a patent the same year. Monier was not the first to think of strengthening concrete with metal, but his patent design clearly established the principle of reinforced concrete for structural more...

At the heart of a quartz watch is a 4-mm bar of quartz piezoelectric crystal that is made to vibrate by applying a small voltage. The crystal is laser trimmed so that it oscillates exactly 32,768 times per second. Higher-frequency crystals would need too large a driving current and guickly drain a watch battery, and lower-frequency ones would be physically too large. The signal, one cycle per second, either drives a second hand or triggers an LCD (liquid crystal display). Quartz is used because it has a very low coefficient of thermal expansion and thus is not affected by changes in the weather. A fairly standard mass- produced quartz watch typically gains or loses less than one second per day. The first quartz oscillator was produced in 1921. By 1927 Warren Marrison, a telecommunications engineer at Bell Laboratories in Canada, had made the first quartz clock. Unfortunately, its valve-driven counting more...

"Getting information off the Internet is like taking a drink from a fire hydrant" Mitchell Kapor, software designer In 1963, the Advanced Research Project Agency (ARPA) unit, set up by the U.S. Defense Department, began to build a computer network. Driven by fear of the Soviet nuclear threat, it aimed to link computers at different locations, so researchers could share data electronically without having fixed routes between them, making the system less vulnerable to attacks—even nuclear ones. Data was converted into telephone signals using a modem (modulator-demodulator), developed at AT&T in the late 1950s. In the 1.960s, key advances were made, including "packet switching"—the system of packaging, labeling, and routing data that enables it to be delivered across the network between machines. Paul Baran (b. 1926) proposed this system, which broke each message down into tiny chunks. These would be fired into the network, which would then route ("switch") the more...

Michael Faraday (1791-1867), one of Britain's foremost physicists, is most famous for discovering principles relating to magnetic induction and the relationship between magnetism and electricity. But Faraday was also an inventive lecturer and actually initiated the tradition of the Christmas lectures at the Royal Institution (the lectures still go on to this day and are televised in the United Kingdom). Faraday even has the honor of having a unit of measurement named after him; the farad is a unit of electrical capacitance. However, an achievement of this scientist that much less often finds its way into the history books is that he also invented the toy balloon. Faraday's career began not in physics but in chemistry. He was appointed as a chemicals assistant at the Royal Institution and performed experiments in this capacity, investigating chlorine and the nature of gases. It was while researching the properties of hydrogen that Faraday more...

"Demeter, goddess of agriculture, ate Pelop's shoulder, but [made him] a prosthetic ivory shoulder." Ampuloves, History of prosthetic The earliest written reference to an artificial limb occurs in an epic Indian poem, the "Rig-Veda," which was compiled between 3500 and 1800 B.C.E. Written in Sanskrit, the poem includes a description of the amputation of the warrior Queen Vishpla's leg during battle. Later fitted with an iron prosthesis by the Ashvins (celestial physicians), she returned to combat. Most authorities doubt the story of Queen Vishpla, and turn to the Histories of Herodotus for the first plausible reference to a prosthetic limb. Herodotus describes how, in the mid sixth century B.C.E., Hegesistratus of Elis, a Persian soldier and seer imprisoned by the Spartans, was sentenced to death, and cut off part of his foot to escape from the stocks. Hegesistratus fashioned a wooden prosthesis to help walk the 30 miles (48 km) more...

“... embracing the fracture with a pair of hot tongs and closing so tight till the weld leans out..." Vannoccio Biringuccio, sixteenth-century writer Welding is the process of joining pieces of metal with heat, pressure, or a combination of both, so that they completely fuse together. The first instance of welding is thought to have been in the smelting of iron ore to create wrought iron, some of the earliest evidence of which was discovered in a Hattic tomb in northern Anatolia, dated to around 2500 B.C.E. Lumps of the iron ore were heated in furnaces until the impurities melted into a slag, trapped in pores in the still solid iron. The hot piece was then hammered to expel the liquid slag and weld together the particles of surrounding iron. Similar methods of heating and hammering were used to join separate pieces of iron, and examples of this were discovered in more...

By the time Isaac Fenn was granted a patent, in 1765, for his distance-measuring hodometer, the device had existed, in various forms and with various names, for centuries. In Roman times it was called an odometer and comprised little more than a wheel that could be pushed along, coupled to a mechanical system for counting the number of revolutions the wheel made, and thus the distance it had traveled. The eighteenth and nineteenth century saw the mapping of India and the division of vast tracts of land into farms in regions such as the United States and Australia. Reasonably accurate surveying and distance measurement became important. The surveyor's perambulator wheel (the "waywiser" or trundle wheel) was in everyday use. The accuracy of this device was good on a smooth surface such as a pavement or macadamed road. On rough terrain, such as farmland, wheel bounce and slippage became a problem more...