The induced voltage across a stationary conductor in a stationary magnetic field __

1. The induced voltage across a stationary conductor in a stationary magnetic field ___.

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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-> In the given passage there are blanks, each of which has been numbered. Against each five words are suggested, one of which fits the blank appropriately. Find out the appropriate word in each case.If China’s state owned commercial banks seem burdened by bad debts, the country’s rural financial sector is even worse. In the villages, the only formal banking institutions are what are known as rural credit co-operatives. These ___(1)___the distinction in China of having been officially declared insolvent. The rural credit co-operatives are ill named. They are often reluctant to___(2)___ and they are not run as cooperatives as they do not ___(3)___ any profits and their customers have no say in their operations. Until 1996, they were offshoots of the Agricultural Bank of China.. Since then they have been ___(4)___by the Central Bank, though they are in reality run by county governments. Even the word ‘rural’ is misleading. ___(5)___ of their deposits are sucked up and put in the urban banking system. Farmers usually find it easier to ___(6)___ from friends or relatives or black market moneylenders. Yet the co-operatives remain a big part of China’s financial system. Last year, they___(7)___1 for 12 percent of deposits and 11 percent of loans. In recent years, commercial banks (in eluding the Agricultural bank) have closed down___(8)___in the countryside. Yet some 40,000 credit co-operatives remain in place with one in almost every township (as the larger villages or smaller) rural loans are___(9)___. If as the government claims, the credit co-operatives are beginning to turn a profit after six years of losses, it is not because they are any better run. In an effort to ___(10)
___ a stagnant rural economy, the central bank has pumped more than $9 billion into them hoping that they will lend more to farmers. But the root causes of their problems remain and the real solution may have to involve a mix of approaches from commercial banking to real cooperatives.(10)
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MCQ->The induced voltage across a stationary conductor in a stationary magnetic field ___.....

MCQ-> In the following passage some of the words have been left out. Read the passage carefully and select the correct answer for the given blank out of the four alternatives.The thoughts, behavior and tastes of fashion, music, television and other ___(1)___ of life of the masses are often seen having a ___(2)___ impact on the living of the society. We tend to get influenced by the lifestyles of our peer group. The changing ways of life of our peers often __(3)____ us to change our ways of looking at life and leading it. It's a human tendency to do what the crowd does. Few have the courage to resist the peer pressure and be their own selves rather than being one among the lot. Peer pressure is bound to affect most of us, both, positively and ___(4)___. The distinction between positive and negative peer pressure lies in a thoughtful analysis of the views of the masses. Following your peers ___(5)___ leaves a negative impact on your life while an analytical approach of looking at peer behavior can act positively. Let us look at the positive and negative effects of peer pressure.television and other ______ of life
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MCQ-> In the following passage some of the words have been left out. Read the passage carefully and select the correct answer for the given blank out of the four alternatives.Books are our __ (1)____ friends. They are our guides. We can learn everything from them. The books contain all the great ___(2)___ of the world's leaders and we can learn them by reading the books. The books help us find ___(3)___ to our questions. The books never fail us. We should read as ___(4)___ books as we can. But all books are not good. So we should ___(5)___ only good books.Books are our ______ friends.
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