Nuclides with the same atomic number, but different mass number are called? ?->(Show Answer!)

1. Nuclides with the same atomic number, but different mass number are called?

Answer: Isotopes

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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-> Analyse the following passage and provide appropriate answers for the questions that follow: Each piece, or part, of the whole of nature is always merely an approximation to the complete truth, or the complete truth so far as we know it. In fact, everything we know is only some kind of approximation, because we know that we do not know all the laws as yet. Therefore, things must be learned only to be unlearned again or, more likely, to be corrected. The principal of science, the definition, almost, is the following: The test of all knowledge is experiment. Experiment is the sole judge of scientific “truth.” But what is the source of knowledge? Where do the laws that are to be tested come from? Experiment, itself, helps to produce these laws, in the sense that it gives us hints. But also needed is imagination to create from these laws, in the sense that it gives us hints. But also needed is imagination to create from these hints the great generalizations – to guess at the wonderful, simple, but very strange patterns beneath them all, and then to experiment to check again whether we have made the right guess. This imagining process is so difficult that there is a division of labour in physics: there are theoretical physicists who imagine, deduce, and guess at new laws, but do not experiment; and then there are experimental physicists who experiment, imagine, deduce, and guess. We said that the laws of nature are approximate: that we first find the “wrong” ones, and then we find the “right” ones. Now, how can an experiment be “wrong”? First, in a trivial way: the apparatus can be faulty and you did not notice. But these things are easily fixed and checked back and forth. So without snatching at such minor things, how can the results of an experiment be wrong? Only by being inaccurate. For example, the mass of an object never seems to change; a spinning top has the same weight as a still one. So a “law” was invented: mass is constant, independent of speed. That “law” is now found to be incorrect. Mass is found is to increase with velocity, but appreciable increase requires velocities near that of light. A true law is: if an object moves with a speed of less than one hundred miles a second the mass is constant to within one part in a million. In some such approximate form this is a correct law. So in practice one might think that the new law makes no significant difference. Well, yes and no. For ordinary speeds we can certainly forget it and use the simple constant mass law as a good approximation. But for high speeds we are wrong, and the higher the speed, the wrong we are. Finally, and most interesting, philosophically we are completely wrong with the approximate law. Our entire picture of the world has to be altered even though the mass changes only by a little bit. This is a very peculiar thing about the philosophy, or the ideas, behind the laws. Even a very small effect sometimes requires profound changes to our ideas.Which of the following options is DEFINITLY NOT an approximation to the complete truth?
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MCQ-> Read the following passage carefully and answer the questions given at the end.The movement to expel the Austrians from Italy and unite Italy under a republican government had been gaining momentum while Garibaldi was away. There was a growing clamour, not just from Giuseppe Mazzini's republicans, but from moderates as well, for a General capable of leading Italy to independence. Even the King of Piedmont, for whom Garibaldi was still an outlaw under sentence of death, subscribed to an appeal for a sword for the returning hero. Meanwhile, the 'year of revolutions', 1848, had occurred in which Louis Philippe had been toppled from the French throne. In Austria, an uprising triggered off insurrections in Venice and Milan, and the Austrian garrisons were forced out. The King of Piedmont, Charles Albert ordered his troops to occupy these cities. There had also been insurrections in Sicily, causing the King Ferdinand II, to grant major constitutional freedoms in 1849, prompting both the Pope and Charles Albert to grant further concessions.Meanwhile, largely ignorant of these developments, Garibaldi was approaching Italy at a leisurely pace, arriving at Nice on 23 June 1848 to a tumultuous reception. The hero declared himself willing to fight and lay down his life for Charles Albert, who he now regarded as a bastion of Italian nationalism.Mazzini and the republicans were horrified, regarding this as outright betrayal: did it reflect Garibaldi's innate simple-mindedness, his patriotism in the war against Austria, or was it part of a deal with the monarchy? Charles Albert had pardoned Garibaldi, but to outward appearances he was still very wary of the General and the Italian Legion he had amassed of 150 'brigands'. The two men met near Mantua, and the King appeared to dislike him instantly. He suggested that Garibaldi's men should join his army and that Garibaldi should go to Venice and captain a ship as a privateer against the Austrians.Garibaldi, meanwhile, met his former hero Mazzini for the first time, and again the encounter was frosty. Seemingly rebuffed on all sides, Garibaldi considered going to Sicily to fight King Ferdinand II of Naples, but changed his mind when the Milanese offered him the post of General - something they badly needed when Charles Albert's Piedmontese army was defeated at Custoza by the Austrians. With around 1,000 men, Garibaldi marched into the mountains at Varese, commenting bitterly: 'The King of Sardinia may have a crown that he holds on to by dint of misdeeds and cowardice, but my comrades and I do not wish to hold on to our lives by shameful actions'.The King of Piedmont offered an armistice to the Austrians and all the gains in northern Italy were lost again. Garibaldi returned to Nice and then across to Genoa, where he learned that, in September 1848, Ferdinand II had bombed Messina as a prelude to invasion - an atrocity which caused him to be dubbed 'King Bomba'. Reaching Livorno he was diverted yet again and set off across the Italian peninsula with 350 men to come to Venice's assistance, but on the way, in Bologna, he learned that the Pope had taken refuge with King Bomba. Garibaldi promptly altered course southwards towards Rome where he was greeted once again as a hero. Rome proclaimed itself a Republic. Garibaldi's Legion had swollen to nearly 1,300 men, and the Grand Duke of Tuscany fled Florence before the advancing republican force.However, the Austrians marched southwards to place the Grand Duke of Tuscany back on his throne. Prince Louis Napoleon of France despatched an army of 7,000 men under General Charles Oudinot to the port of Civitavecchia to seize the city. Garibaldi was appointed as a General to defend Rome.The republicans had around 9,000 men, and Garibaldi was given control of more than 4,000 to defend the Janiculum Hill, which was crucial to the defence of Rome, as it commanded the city over the Tiber. Some 5,000 well-equipped French troops arrived on 30 April 1849 at Porta Cavallegeri in the old walls of Rome, but tailed to get through, and were attacked from behind by Garibaldi, who led a baton charge and was grazed by a bullet slightly on his side. The French lost 500 dead and wounded, along with some 350 prisoners, to the Italians, 200 dead and wounded. It was a famous victory, wildly celebrated by the Romans into the night, and the French signed a tactical truce.However, other armies were on the march: Bomba's 12,500-strong Neapolitan army was approaching from the south, while the Austrians had attacked Bologna in the north. Garibaldi too, a force out of Rome and engaged in a flanking movement across the Neapolitan army's rear at Castelli Romani; the Neapolitans attacked and were driven off leaving 50 dead. Garibaldi accompanied the Roman General, Piero Roselli, in an attack on the retreating Neapolitan army. Foolishly leading a patrol of his men right out in front of his forces, he tried to stop a group of his cavalry retreating and fell under their horses, with the enemy slashing at him with their sabres. He was rescued by his legionnaires, narrowly having avoided being killed, but Roselli had missed the chance to encircle the Neapolitan army.Garibaldi boldly wanted to carry the fight down into the Kingdom of Naples, but Mazzini, who by now was effectively in charge of Rome, ordered him back to the capital to face the danger of Austrian attack from the north. In fact, it was the French who arrived on the outskirts of Rome first, with an army now reinforced by 30,000. Mazzini realized that Rome could not resist and ordered a symbolic stand within the city itself, rather than surrender, for the purposes of international propaganda and to keep the struggle alive, whatever the cost. On 3 June the French arrived in force and seized the strategic country house, Villa Pamphili.Garibaldi rallied his forces and fought feverishly to retake the villa up narrow and steep city streets, capturing it, then losing it again. By the end of the day, the sides had 1,000 dead between them. Garibaldi once again had been in the thick of the fray, giving orders to his troops and - fighting, it was said, like a lion. Although beaten 'off for the moment, the French imposed a siege in the morning, starving the city of provisions and bombarding its beautiful centre.On 30 June the French attacked again in force, while Garibaldi, at the head of his troops, fought back ferociously. But there was no prospect of holding the French off indefinitely, and Garibaldi, decided to take his men out of the city to continue resistance in the mountains. Mazzini fled to Britain while Garibaldi remained to fight for the cause. He had just 4,000 men, divided into two legions, and faced some 17,000 Austrians and Tuscans in the north, 30,000 Neapolitans and Spanish in the south, and 40,000 French in the west. He was being directly pursued by 8,000 French and was approaching Neapolitan and Spanish divisions of some 18,000 men. He stood no chance whatever. The rugged hill country was ideal, however, for his style of irregular guerrilla warfare, and he manoeuvred skilfully, marching and counter-marching in different directions, confounding his pursuers before finally aiming for Arezzo in the north. But his men were deserting in droves and local people were hostile to his army: he was soon reduced to 1500 men who struggled across the high mountain passes to San Marino where he found temporary. refuge.The Austrians, now approaching, demanded that he go into exile in America. He was determined to fight on and urged the ill and pregnant Anita, his wife, to stay behind in San Marino, but she would not hear of it. The pair set off with 200 loyal soldiers along the mountain tracks to the Adriatic coast, from where Garibaldi intended to embark for Venice which was still valiantly holding out against the Austrians. They embarked aboard 13 fishing boats and managed to sail to within 50 miles of the Venetian lagoon before being spotted by an Austrian flotilla and fired upon.Only two of Garibaldi's boats escaped. He carried Anita through the shallows to a beach and they moved further inland. The ailing Anita was placed in a cart and they reached a farmhouse, where she died. Her husband broke down into inconsolable wailing and she was buried in a shallow grave near the farmhouse, but was transferred to a churchyard a few days later. Garibaldi had no time to lose; he and his faithful companion Leggero escaped across the Po towards Ravenna.At last Garibaldi was persuaded to abandon his insane attempts to reach Venice by sea and to return along less guarded routes on the perilous mountain paths across the Apennines towards the western coast of Italy. He visited his family in Nice for an emotional reunion with his mother and his three children - but lacked the courage to tell them what had happened to their mother.Find the correct statement:
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MCQ->Nuclides with the same atomic number, but different mass number are called?...

MCQ->Nuclides with the same atomic number ,but different mass number are called...