Text 7 b

It is interesting to know…

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After inventing dynamite, Swedish-born Alfred Nobel became a very rich man. However, he foresaw its universally destructive powers too late. Nobel preferred not to be remembered as the inventor of dynamite, so in 1895, just two weeks before his death, he created a fund to be used for awarding prizes to people who had made worthwhile contributions to mankind. Originally there were five awards: literature, physics, chemistry, medicine, and peace. Economics was added in 1968, just sixty-seven years after the first-awards ceremony.

Nobel's original legacy of nine million dollars was invested, and the interest on this sum is used for the awards which vary from $30,000 to $125,000.

Every year on December 10, the anniversary of Nobel's death, the awards (gold medals, illuminated diploma, and money) are presented to the winners. Sometimes politics plays an important role in the judges' decisions. Americans have won numerous science awards, but relatively few literature prizes.

No awards were presented from 1940 to 1942 at the beginning of World War II. Some people have won two prizes, but this is rare; others have shared their prizes.

Text 7 c einstein’s photoelectric law

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To explain the characteristics of thermal radiation, that is, the radiation emitted by hot bodies, Planck (1900) suggested that the emission and absorption of radiant energy by matter is in discrete quanta of energy h.

Einstein (1905) extended this hypothesis and postulated the quantum nature of radiation itself.

It is further seen that the absence of a time lag in photoelectric emission arises naturally, the absorption of quantum energy is instantaneous as is the resultant emission of an electron. This is to be contrasted with the hitherto accepted view that radiation consists of waves; the energy in the incident beam is spread uniformly over the area of the surface on which it falls. An electron which is at the surface or near it requires some time (of the order of seconds), to absorb sufficient energy from the beam to be able to escape from the surface.

The simplicity of Einstein’s equation conceals the revolutionary nature of the concept underlying it. Light and all forms of radiation are emitted, and absorbed, in quanta of energy, the quanta are localized in space.

This is in fact a corpuscular theory, a beam of light or other radiation consisting of a stream of corpuscles called photons. Every photon moves with the velocity of light, and has a definite energy hv.

The study of the photoelectric effect was of major importance for the development of physical theory during the first two decades of the 20th century. The role played by the photoelectric effect during this period was largely due to the manner in which it displayed the quantum properties of radiation, which are not describable by the electromagnetic wave theory.

Unit 8 Grammar :

Infinitive (forms and functions).

Reading exercises