English for students of Physics_Unit 8

33 Unit Eight OPTICS READING PASSAGE Spectral analysis We mentioned compounds of calcium, lithium, and strontium without specifying which compounds we were talking about. This may have given you the impression that only the spectrum of one of the elements in a compound can be observed. It is true that the flame of your alcohol burner is hot enough to produce the spectra of sodium, lithium, calcium, copper, and a few other elements, but that is not hot enough to produce the other spectra of elements, such as oxygen and chlorine. However, if we heat a sample of a compound to a sufficiently high temperature (for example, by putting it in an electric arc), the spectra of all the elements in the compound will be observed. Under such conditions, the resulting spectrum is no longer simple. It will most likely contain complicated patterns of many closely spaced lines. Yet each element gives out its own spectrum, which is different from that of any other. It takes accurate measurements of the positions of spectral lines to identify an element. Once this has been done, however, the presence of that element has been definitely established. With a good instrument, it is observed that the yellow of the sodium flame is not just any yellow. It is a very specific color indeed, which has its own special place in the spectrum. It is a yellow made by no other element. The presence of this particular pair of lines always means that sodium is present in the light source. Even if the yellow color is hidden from the unaided eye by many colors, the spectroscope will show the presence of sodium. Although calcium, lithium, and strontium give flame tests of nearly the same color, each gives its own set of characteristic spectral lines when viewed through a spectroscope. The spectroscope thus enables us to distinguish one element from another. Spectral analysis, or spectroscopy, can be done on tiny quantities of matter, such as very small sample of a rare mineral or of a biological material. Spectroscopy can even be used to determine the presence of different elements in distant objects like our sun and other stars. Analysis of sunlight was one of the very early uses of spectroscope in the study of unknown matter. Most of the spectral lines observed in sunlight could also be produced with known material in the laboratory. However, during a solar eclipse in 1868, a new set of spectral lines was found in the spectrum of the light coming from the edge of the sun. This set of lines had never been seen before and could not be produced with any element known at the time. The lines were therefore thought to be from a new element, which was given the name 34 "helium" after the Greek word for sun. Eventually, the element was also detected on earth through the use of a spectroscope. During the first few years of spectroscopy, five new elements were discovered that are present on earth in such a small concentrations that they were previously unknown. For example, in analyzing the spectrum of minerals found in the water of a certain spring in Germany, two lines of unknown origin were found in the blue region of the spectrum. This bit of evidence was enough to challenge Robert Bunsen, the German chemist, to search for a new element in the water. In order to isolate some of the pure element, which he named "cesium"; it was necessary to evaporate 40,000kg of spring water! In more recent times, spectral analysis has been one of the tools found helpful in identifying some of the new elements produced by nuclear reactions. Time after time, this interplay between chemical analysis and spectral analysis has caused complex substances to yield the secret of their composition. Invariably, the results given by these two different methods agree completely. (From Uri Haber-Schaim. et al; Introductory Physical Science; Prentice Hall, Inc; Englewood Cliffs, New Jersey 07632;1987). READING COMPREHENSION Exercise 1: Answer the following questions by referring to the reading passage 1. How are the spectra of all elements in a compound completely observed? ………………………………………………………………………………………… ………..…………………………………………………………………… 2. Why is the yellow color of a sodium flame not just any yellow but a specific one? ………………………………………………………………………………………… ………..…………………………………………………………………… 3. What is the term used to refer to spectral analysis? ………………………………………………………………………………………… ………..…………………………………………………………………… 4. What is the major function of spectroscopy? ………………………………………………………………………………………… ………..…………………………………………………………………… 5. In the very present, in which way spectroscopy is more helpful? ………………………………………………………………………………………… ………..…………………………………………………………………… 35 Exercise 2: Decide whether each of the following statements is true (T) or false (F) or without any information to identify (N). 1. …………. It is impossible to see the spectra of oxygen and chlorine by using alcohol burner. 2. ………….The positions of spectral lines of an element help identify the element. 3. ………….Some elements may have some similar spectral lines. 4. ………….Calcium, lithium and strontium give the same spectra. 5. ………….Applying spectral analysis helps to detect new elements. Exercise 3: Matching each of the words/phrases from column I with its definition from column II Column I Column II 1. to observe 2. flame 3. sample 4. pattern 5. accurate 7. to identify a. precise b. to tell the difference c. a large amount of something in a small area. d. a long and pointed stream of burning gas e. to recognize f. to discover 8. specific g. a small amount of a substance scientifically 9. to determine examined and analyzed 10. to distinguish 11. concentration h. a particular way for something to be done or to occur i. to watch carefully k. particular GRAMMAR IN USE: The passive Read the following two paragraphs: Paragraph one: Sir Joseph John Thomson (1846-1940) is a British physicist and mathematician and was the head of a group of researchers at Cavendish Laboratory in Cambridge. Thompson discovered the electron. He is regarded as the founder of modern physics. 36 Paragraph two: Electron is a subatomic particle and one of the basic constituents of matter. The electron was discovered by J.J. Thomson. It is found in all atoms and contains the smallest known negative electrical charge. Compare the two sentences, one from each paragraph Thomson discovered the electron. And The electron was discovered by Thomson. The two sentences have the same meaning but different topics: they are about different things, hence having different implications. In the former one, the topic is Thomson while in the latter one the electron. We say the two sentences have different subjects. So what is the significance of the difference between the two ways of saying? The answer really lies in whether we want to lay emphasis on the doer of the action (we call it the agent) or the action (sometimes the result of the action) itself. In this pair of sentences, the first one is called an active sentence while the second is called passive sentence. Look at the verb phrase of each sentence: "discovered" and "was discovered" Therefore, we deduce that the verb phrase in passive sentences is formed by combining the auxiliary verb to be and a passive particle (exactly the same form as a part participle) To be + PII In which the auxiliary verb to be bears all the grammatical changes in tenses and aspects and others. 1. Present tenses: 1. Many elements are not so easily identified. 2. Once this has been done, however, the presence of that element has been definitely established. 3. When the experiment is being conducted, there should be no changes in ambient temperature. 2. Past tenses: 1. During the first five years of spectroscopy, five new elements were discovered that are present on earth in such small concentrations that they were previously unknown. 2. This set of lines had never been seen before. 3. Eventually, the element was also detected on earth through the use of a spectroscopy. 4. While the experiment was being conducted, the ambient temperature was kept unchanged. 3. With “modal verbs”: The passive sentences with modal verbs are formed as follows: Modal verb + be + PII 37 a. This may have given you the impression that only the spectrum of one of the element in a compound can be observed. b. Spectral analysis, or spectroscopy, can be done on tiny quantities of matter. c. Spectroscopy can be even used to determine the presence of different elements in distant objects like our sun and stars. d. Most of the spectral lines observed in sunlight could also be produced with known materials in the laboratory. e. This set of lines could not be produced with any element known at the time. Note: 1. As for verbs with prepositions or particles, the preposition and particle remain in its position with respect to the verb. For example: The same volume of hydrogen is added to the tube. 2. From the sample paragraphs and all the examples taken out from the reading text, we can deduce that, in writing a science report or description, the use of passive sentences is commonly resorted to. And more commonly, the impersonal passive is used: Have another look at the passive sentence in the pair of sentences taken out from the two sample paragraphs: The electron was discovered by J. J. Thomson. The underlined phrase is called by-phrase (forming by by + agent). This gives the new information (by whom) to clarify the topic (subject) which is an already -known piece of information (the electron was discovered). However, in science documents, the actions and their result are much more important, the by-phrase becomes little important, hence forming the impersonal passive to be frequently used. In scientific documents, the following special patterns of passive are taken much use of: 1. The passive with get: Instead of be, sometimes we use get to form passive sentences: Example: 1. If the spring is stretched beyond its elastic limit, it will get deformed. 2. Everything gets attracted to the center of the earth no matter where they are. 3. When you do the experiment, be careful or you may get burned. However, get is mainly used in informal English, and it has more limited use than be. The passive with get expresses action and change, not a state. It often refers to something happening by accident, unexpectedly or incidentally. ... - tailieumienphi.vn