The emission of electrons from a metal plate exposed to light depends on the : ?->(Show Answer!)

1. The emission of electrons from a metal plate exposed to light depends on the :

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MCQ->The emission of electrons from a metal plate exposed to light depends on the :....

MCQ-> Study the following graph and answer the questions that follow

France, South Africa, Australia, Ukraine and Poland form an energy consortium which declares $$CO_2$$ emission of 350 million ton per annum as standard benchmark. The energy consortium decides to sell their carbon emission savings against the standard benchmark to high carbon emission countries. It is expected that the per capita income of each country of the energy consortium increases by 2%, 2.5% and 3.5% p.a. for the next three years respectively. The ratio of $$CO_2$$ emission to per capita income of the each energy consortium country reduces by 50% and remains constant for the next three years. By selling 0.5 $$CO_2$$ emissions [million ton] the energy consortium earns 1.25 carbon credits, then determine the total carbon credits earned by energy consortium in three years.
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MCQ->Assertion (A): The amount of photoelectric emission depends on the intensity of incident light. Reason (R): Photo electric emission can occur only if frequency of incident light is less than threshold frequency.

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MCQ-> In the modern scientific story, light was created not once but twice. The first time was in the Big Bang, when the universe began its existence as a glowing, expanding, fireball, which cooled off into darkness after a few million years. The second time was hundreds of millions of years later, when the cold material condensed into dense suggests under the influence of gravity, and ignited to become the first stars.Sir Martin Rees, Britain’s astronomer royal, named the long interval between these two enlightements the cosmic ‘Dark Age’. The name describes not only the poorly lit conditions, but also the ignorance of astronomers about that period. Nobody knows exactly when the first stars formed, or how they organized themselves into galaxies — or even whether stars were the first luminous objects. They may have been preceded by quasars, which are mysterious, bright spots found at the centres of some galaxies.Now two independent groups of astronomers, one led by Robert Becker of the University of California, Davis, and the other by George Djorgovski of the Caltech, claim to have peered far enough into space with their telescopes (and therefore backwards enough in time) to observe the closing days of the Dark age.The main problem that plagued previous efforts to study the Dark Age was not the lack of suitable telescopes, but rather the lack of suitable things at which to point them. Because these events took place over 13 billion years ago, if astronomers are to have any hope of unravelling them they must study objects that are at least 13 billion light years away. The best prospects are quasars, because they are so bright and compact that they can be seen across vast stretches of space. The energy source that powers a quasar is unknown, although it is suspected to be the intense gravity of a giant black hole. However, at the distances required for the study of Dark Age, even quasars are extremely rare and faint.Recently some members of Dr Becker’s team announced their discovery of the four most distant quasars known. All the new quasars are terribly faint, a challenge that both teams overcame by peering at them through one of the twin Keck telescopes in Hawaii. These are the world’s largest, and can therefore collect the most light. The new work by Dr Becker’s team analysed the light from all four quasars. Three of them appeared to be similar to ordinary, less distant quasars. However, the fourth and most distant, unlike any other quasar ever seen, showed unmistakable signs of being shrouded in a fog because new-born stars and quasars emit mainly ultraviolet light, and hydrogen gas is opaque to ultraviolet. Seeing this fog had been the goal of would-be Dark Age astronomers since 1965, when James Gunn and Bruce Peterson spelled out the technique for using quasars as backlighting beacons to observe the fog’s ultraviolet shadow.The fog prolonged the period of darkness until the heat from the first stars and quasars had the chance to ionise the hydrogen (breaking it into its constituent parts, protons and electrons). Ionised hydrogen is transparent to ultraviolet radiation, so at that moment the fog lifted and the universe became the well-lit place it is today. For this reason, the end of the Dark Age is called the ‘Epoch of Re-ionisation’. Because the ultraviolet shadow is visible only in the most distant of the four quasars, Dr Becker’s team concluded that the fog had dissipated completely by the time the universe was about 900 million years old, and oneseventh of its current size.In the passage, the Dark Age refers to
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MCQ->The simplest method of welding two pieces of metal together is known as pressure welding.The ends of a metal are heated to a white heat-for iron,the welding temperature should be about 1300C-in a flame.At this temperature the metal becomes plastic.The ends are pressed or hammered together,and the joint is smoothed off.Care must be taken to ensure that surfaces are thoroughly clean first,for dirt will weaken the weld.Moreover,the heating of iron or steel to a high temperature cause oxidation,and a film of oxide is added to the heated surfaces.For this reason,flux is applied to the heated metal.At welding heat,flux melts and the oxide particles are dissolved in it together with any other impurities which may be present.The metal surfaces are pressed together,and the flux is squeezed out from the center of the weld.A number of different types of weld may be used,but for fairly thick bars of metals,a vee-shaped belt should be normally employed.It is rather stronger than ordinary butt weld. The simplest way of welding two pieces of metal together is....