Rajasthan State Exams

Until the mid-nineteenth century, the most powerful known explosive was gunpowder. In 1846 Italian chemist Ascanio Sobrero discovered that by nitrating glycerin he could make a fearsomely explosive liquid. It was also frighteningly unstable. Alfred Nobel (1833- 1896) undertook the dangerous task of turning nitroglycerin into a marketable product. Despite an explosion in 1864 that killed his brother and workers at the family's factory, he persisted with his experiments. Nobel's first success came from combining nitroglycerin with a mercury fulminate detonator. He began producing this explosive in bulk, but the frequency of accidents soon saw it banned in many countries. In 1866 Nobel discovered a mixture of nitroglycerin with diatomaceous earth, a chalklike sedimentary rock. He christened this comparatively safe explosive dynamite, from the Greek word for "power." Packed into paper tubes, dynamite was soon selling in vast quantities and revolutionized activities such as tunnel-building and quarrying. Dynamite, patented in more...

Long before the snowmobile, our ancestors found an environmentally friendly way to get around in the snow—the sledge. In fact, the sledge (and variations on its theme) was key in many areas of ancient life. A sled is a vehicle that moves by sliding across the ground. Sleighs are horse-drawn vehicles, with passenger seating. Sledges tend to be large vehicles consisting of a wooden base mounted on smooth runners, useful for transporting large objects. Evidence of wooden sledge usage reaches back to 7000 B.C.E., to peoples living in the Arctic regions of northern Europe. Initially sledges may have been pulled by humans, but with time dogs and oxen were commandeered to take the strain. Inuits have used dog-sleds since pre-Columbian times. Sledge use has extended to hotter climates, too, including the dry, dusty lands of Mesopotamia. Exactly where and when the sledge was developed is unknown, but it is likely more...

The study of human memory was greatly changed in 1943, when Warren McCulloch and Walter Pitts wrote a paper on how neurons might work. (Neurons are the cells that make up tissue in the part of the nervous system involved in learning and recognition.) Six years later, D. O. Hebb described the strengthening of neural connections that occurred each time they were used. In the early days of artificial intelligence research, Frank Rosenblatt (1928-1971)—a computer scientist at the Cornell Aeronautical Laboratory in New York—was studying how the eyes of a fly work. Rosenblatt observed that when a fly perceives danger, its reaction occurs faster than the information can be processed by its brain. He then produced the perceptron, the first computer to learn new skills using a neural network mimicking human thought processes. The perceptron had a layer of interconnected input and output nodes. Each connection is "weighted" to make more...

After India got Independence, a controversy was at its peak whether English should continue or not. The two views ? gave their own arguments in for and against the existence o; English in India after freedom. Some people opposed English because they thought that it was a foreign language, the language of the British and therefore with the end of their rule, their language should also be abolished. But it was not easy to abolish it at once. Hence it was given a lease of fifteen years and after that it was to be replaced by Hindi as the national and official language of the country. But when the time for the replacement of English by Hindi came, there was lot of opposition from all sides especially from the south. Nothing could be done in such an atmosphere and finally it was decided that English would remain the official language more...

Whether it is for a mobile phone or an iPod, the modern way of life relies upon rechargeable batteries.  The first steps along this path were taken by the French physicist Gaston Plante (1834-1889). Working in Paris in 1859, Plante invented the lead- acid cell. His device comprised a coil of lead for the negative plate and a coil of lead oxide for the positive plate; these were separated by rubber strips and bathed in a bath of dilute sulfuric acid. The sulfuric acid reacts with the lead, releasing electrons that pass to the positive plate, hence generating current. Existing cells ceased to produce current when the chemical reactants were spent. But, in the Plante arrangement, the reaction is reversed when current is added to the cell from an outside source, and in so doing the battery is recharged. Within a year, Plante had fitted nine of these units into more...

Our country had been under the British rule for about two hundred years. This long term foreign rule suppressed India and his people ruthlessly and it seemed for a while that she (India) would never raise her head in the free air. But Mahatma Gandhi's efforts and his right direction made it possible and the Britishers went to their home land for good. India got independence in 1947. Since then the leaders and the politicians have been trying their best to improve the condition of the masses. Many achievements have been made already but still there are many more to achieve for the alround development of India. In the economic field, unprecedented progress has been made so far. Our five-year plans have been successfully completed with shining results. Many multipurpose projects such as Bhakra Nangal, Hirakund and Damodar valley projects, etc. have been taken in hand and completed in time. more...

Wrapping up warm to toil against the elements has one problem: you can get too warm. Donning a fleece or heavy overcoat might protect you from the wind and rain, but any serious physical exertion will leave you hot and sweaty. Step forward GORE-TEX* a synthetic fabric that keeps you dry while allowing theskin to breathe. GORE-TEX" is produced by expanding polytetra-fluoroethylene (PTFE)-a polymer comprising long carbon-fluorine chains—under high temperature. The material contains many pores, allowing perspiration from the wearer to evaporate and escape. The pores arc, however, much too small to allow passage of water droplets, rendering the material impenetrable to the elements. For comfort and protection, the special membrane is normally sandwiched between several fabric layers. The invention of GORE-TEX* was a family effort; it was developed by Wilbert L. Gore (1912-1986) and his son Robert W. Gore, plus Rowena Taylor. In 1958, Gore Senior and his wife more...

Hobbies enable us to spend our leisure hours. Different people can have different type of hobbies. Hobbies bring occupation in our idle hours. They keep us away from bad habits. They help us to forget our pains and loneliness of life. Sometimes it may help us in bringing a considerable amount of money, but money can never be supposed as a profession. Hobbies depend upon the taste and tendencies of the individual there are many types of hobbies, stamp  Collection, coins collection, motor-driving, kite flying, swimming, cooking, gardening, photography etc . The hobbies keep on changing with passage of life. We have different hobbies in our childhood- They change as we mature and go on changing with the passage of time. The pursuits of childhood always diverts with the passage of time. As I am a lover of nature gardening is my favourite hobby. Our house is very spacious. We more...

A rat is a very common creature. It is found everywhere in the world. It is a very small creature. A rat has four legs, two eyes, two ears and a long tail. It has small sharp claws at the end of the legs. Its tiny teeth are also very sharp. It is normally gray in colour. A rat lives in holes in fields and houses. It lives mainly on grains like rice and wheat. A rat is a very mischievous creature. It causes a great harm and damage to property. It keeps gnawing at everything that it may get. Actually, its teeth continue to grow, due to which it has to keep gnawing.                          A rat is very dangerous too. It carries germs of different dreadful diseases like plague. This disease sometimes breaks out in the form of more...

"The key to success is to risk thinking unconventional thoughts. Convention is the enemy of progress." Trevor Baylis The evolution of the battery-free radio is a curiously British success story. The tale begins in 1991 with part- time inventor Trevor Baylis (b. 1937) watching a television documentary about the spread of AIDS in Africa. It suggested that the epidemic could only be halted through education. A major problem, however. was that poverty and a lack of basic technology made communication to remote parts of Africa difficult. Baylis saw an immediate solution—a simple and cheap radio set that required no household current or battery power to operate. Crudely cobbling together parts from an old transistor radio, a small electric motor from a toy car, and the clockwork mechanism from a music box, he created a prototype powered by a clockwork wind-up mechanism that drove a tiny internal electrical generator. Fully wound, more...