The circuit in figure, the switched on at t = 0. After a long time the current through 5 Ω resistance is ?->(Show Answer!)

1. The circuit in figure, the switched on at t = 0. After a long time the current through 5 Ω resistance is

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MCQ-> In a modern computer, electronic and magnetic storage technologies play complementary roles. Electronic memory chips are fast but volatile (their contents are lost when the computer is unplugged). Magnetic tapes and hard disks are slower, but have the advantage that they are non-volatile, so that they can be used to store software and documents even when the power is off.In laboratories around the world, however, researchers are hoping to achieve the best of both worlds. They are trying to build magnetic memory chips that could be used in place of today’s electronics. These magnetic memories would be nonvolatile; but they would also he faster, would consume less power, and would be able to stand up to hazardous environments more easily. Such chips would have obvious applications in storage cards for digital cameras and music- players; they would enable handheld and laptop computers to boot up more quickly and to operate for longer; they would allow desktop computers to run faster; they would doubtless have military and space-faring advantages too. But although the theory behind them looks solid, there are tricky practical problems and need to be overcome.Two different approaches, based on different magnetic phenomena, are being pursued. The first, being investigated by Gary Prinz and his colleagues at the Naval Research Laboratory (NRL) in Washington, D.c), exploits the fact that the electrical resistance of some materials changes in the presence of magnetic field— a phenomenon known as magneto- resistance. For some multi-layered materials this effect is particularly powerful and is, accordingly, called “giant” magneto-resistance (GMR). Since 1997, the exploitation of GMR has made cheap multi-gigabyte hard disks commonplace. The magnetic orientations of the magnetised spots on the surface of a spinning disk are detected by measuring the changes they induce in the resistance of a tiny sensor. This technique is so sensitive that it means the spots can be made smaller and packed closer together than was previously possible, thus increasing the capacity and reducing the size and cost of a disk drive. Dr. Prinz and his colleagues are now exploiting the same phenomenon on the surface of memory chips, rather spinning disks. In a conventional memory chip, each binary digit (bit) of data is represented using a capacitor-reservoir of electrical charge that is either empty or fill -to represent a zero or a one. In the NRL’s magnetic design, by contrast, each bit is stored in a magnetic element in the form of a vertical pillar of magnetisable material. A matrix of wires passing above and below the elements allows each to be magnetised, either clockwise or anti-clockwise, to represent zero or one. Another set of wires allows current to pass through any particular element. By measuring an element’s resistance you can determine its magnetic orientation, and hence whether it is storing a zero or a one. Since the elements retain their magnetic orientation even when the power is off, the result is non-volatile memory. Unlike the elements of an electronic memory, a magnetic memory’s elements are not easily disrupted by radiation. And compared with electronic memories, whose capacitors need constant topping up, magnetic memories are simpler and consume less power. The NRL researchers plan to commercialise their device through a company called Non-V olatile Electronics, which recently began work on the necessary processing and fabrication techniques. But it will be some years before the first chips roll off the production line.Most attention in the field in focused on an alternative approach based on magnetic tunnel-junctions (MTJs), which are being investigated by researchers at chipmakers such as IBM, Motorola, Siemens and Hewlett-Packard. IBM’s research team, led by Stuart Parkin, has already created a 500-element working prototype that operates at 20 times the speed of conventional memory chips and consumes 1% of the power. Each element consists of a sandwich of two layers of magnetisable material separated by a barrier of aluminium oxide just four or five atoms thick. The polarisation of lower magnetisable layer is fixed in one direction, but that of the upper layer can be set (again, by passing a current through a matrix of control wires) either to the left or to the right, to store a zero or a one. The polarisations of the two layers are then either the same or opposite directions.Although the aluminum-oxide barrier is an electrical insulator, it is so thin that electrons are able to jump across it via a quantum-mechanical effect called tunnelling. It turns out that such tunnelling is easier when the two magnetic layers are polarised in the same direction than when they are polarised in opposite directions. So, by measuring the current that flows through the sandwich, it is possible to determine the alignment of the topmost layer, and hence whether it is storing a zero or a one.To build a full-scale memory chip based on MTJs is, however, no easy matter. According to Paulo Freitas, an expert on chip manufacturing at the Technical University of Lisbon, magnetic memory elements will have to become far smaller and more reliable than current prototypes if they are to compete with electronic memory. At the same time, they will have to be sensitive enough to respond when the appropriate wires in the control matrix are switched on, but not so sensitive that they respond when a neighbouring elements is changed. Despite these difficulties, the general consensus is that MTJs are the more promising ideas. Dr. Parkin says his group evaluated the GMR approach and decided not to pursue it, despite the fact that IBM pioneered GMR in hard disks. Dr. Prinz, however, contends that his plan will eventually offer higher storage densities and lower production costs.Not content with shaking up the multi-billion-dollar market for computer memory, some researchers have even more ambitious plans for magnetic computing. In a paper published last month in Science, Russell Cowburn and Mark Well and of Cambridge University outlined research that could form the basis of a magnetic microprocessor — a chip capable of manipulating (rather than merely storing) information magnetically. In place of conducting wires, a magnetic processor would have rows of magnetic dots, each of which could be polarised in one of two directions. Individual bits of information would travel down the rows as magnetic pulses, changing the orientation of the dots as they went. Dr. Cowbum and Dr. Welland have demonstrated how a logic gate (the basic element of a microprocessor) could work in such a scheme. In their experiment, they fed a signal in at one end of the chain of dots and used a second signal to control whether it propagated along the chain.It is, admittedly, a long way from a single logic gate to a full microprocessor, but this was true also when the transistor was first invented. Dr. Cowburn, who is now searching for backers to help commercialise the technology, says he believes it will be at least ten years before the first magnetic microprocessor is constructed. But other researchers in the field agree that such a chip, is the next logical step. Dr. Prinz says that once magnetic memory is sorted out “the target is to go after the logic circuits.” Whether all-magnetic computers will ever be able to compete with other contenders that are jostling to knock electronics off its perch — such as optical, biological and quantum computing — remains to be seen. Dr. Cowburn suggests that the future lies with hybrid machines that use different technologies. But computing with magnetism evidently has an attraction all its own.In developing magnetic memory chips to replace the electronic ones, two alternative research paths are being pursued. These are approaches based on:
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MCQ->The circuit in figure, the switched on at t = 0. After a long time the current through 5 Ω resistance is....

MCQ-> In the annals of investing, Warren Buffett stands alone. Starting from scratch, simply by picking stocks and companies for investment, Buffett amassed one of the epochal fortunes of the twentieth century. Over a period of four decades more than enough to iron out the effects of fortuitous rolls of the dice, Buffett outperformed the stock market, by a stunning margin and without taking undue risks or suffering a single losing year. Buffett did this in markets bullish and bearish and through economies fat and lean, from the Eisenhower years to Bill Clinton, from the l950s to the l990s, from saddle shoes and Vietnam to junk bonds and the information age. Over the broad sweep of postwar America, as the major stock averages advanced by 11 percent or so a year, Buffett racked up a compounded annual gain of 29.2 percent. The uniqueness of this achievement is more significant in that it was the fruit of old-fashioned, long-term investing. Wall Street’s modern financiers got rich by exploiting their control of the public's money: their essential trick was to take in and sell out the public at opportune moments. Buffett shunned this game, as well as the more venal excesses for which Wall Street is deservedly famous. In effect, he rediscovered the art of pure capitalism, a cold-blooded sport, but a fair one. Buffett began his career, working out his study in Omaha in 1956. His grasp of simple verities gave rise to a drama that would recur throughout his life. Long before those pilgrimages to Omaha, long before Buffett had a record, he would stand in a comer at college parties, baby-faced and bright-eyed, holding forth on the universe as a dozen or two of his older, drunken fraternity brothers crowded around. A few years later, when these friends had metamorphosed into young associates starting out on Wall Street, the ritual was the same. Buffett, the youngest of the group, would plop himself in a big, broad club chair and expound on finance while the others sat at his feet. On Wall Street, his homespun manner made him a cult figure. Where finance was so forbiddingly complex, Buffett could explain it like a general-store clerk discussing the weather. He never forgot that underneath each stock and bond, no matter how arcane, there lay a tangible, ordinary business. Beneath the jargon of Wall Street, he seemed to unearth a street from small-town America. In such a complex age, what was stunning about Buffett was his applicability. Most of what Buffett did was imitable by the average person (this is why the multitudes flocked to Omaha). It is curious irony that as more Americans acquired an interest in investing, Wall Street became more complex and more forbidding than ever. Buffett was born in the midst of depression. The depression cast a long shadow on Americans, but the post war prosperity eclipsed it. Unlike the modern portfolio manager, whose mind- set is that of a trader, Buffett risked his capital on the long term growth of a few select businesses. In this, he resembled the magnates of a previous age, such as J P Morgan Sr.As Jack Newfield wrote of Robert Kennedy, Buffett was not a hero, only a hope; not a myth, only a man. Despite his broad wit, he was strangely stunted. When he went to Paris, his only reaction was that he had no interest in sight-seeing and that the food was better in Omaha. His talent sprang from his unrivaled independence of mind and ability to focus on his work and shut out the world, yet those same qualities exacted a toll. Once, when Buffett was visiting the publisher Katharine Graham on Martha’s Vineyard, a friend remarked on the beauty of the sunset. Buffett replied that he hadn't focused on it, as though it were necessary for him to exert a deliberate act of concentration to "focus" on a sunset. Even at his California beachfront vacation home, Buffett would work every day for weeks and not go near the water. Like other prodigies, he paid a price. Having been raised in a home with more than its share of demons, he lived within an emotional fortress. The few people who shared his office had no knowledge of the inner man, even after decades. Even his children could scarcely recall a time when he broke through his surface calm and showed some feeling. Though part of him is a showman or preacher, he is essentially a private person. Peter Lynch, the mutual-fund wizard, visited Buffett in the 1980s and was struck by the tranquility in his inner sanctum. His archives, neatly alphabetized in metal filing cabinets, looked as files had in another era. He had no armies of traders, no rows of electronic screens, as Lynch did. Buffett had no price charts, no computer - only a newspaper clipping from 1929 and an antique ticker under a glass dome. The two of them paced the floor, recounting their storied histories, what they had bought, what they had sold. Where Lynch had kicked out his losers every few weeks, Buffett had owned mostly the same few stocks for years and years. Lynch felt a pang, as though he had traveled back in time. Buffett’s one concession to modernity is a private jet. Otherwise, he derives little pleasure from spending his fabulous wealth. He has no art collection or snazzy car, and he has never lost his taste for hamburgers. He lives in a commonplace house on a tree-lined block, on the same street where he works. His consuming passion - and pleasure - is his work, or, as he calls it, his canvas. It is there that he revealed the secrets of his trade, and left a self-portrait.“Saddle shoes and Vietnam”, as expressed in the passage, refers to: I. Denier cri and Vietnam war II. Growth of leather footwear industry and Vietnam shoe controversy III. Modern U.S. population and traditional expatriates IV. Industrial revolution and Vietnam Olympics V. Fashion and Politics....

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