Химия B. Text Study просмотров - 163
A. Text Study
I. Look at the title. What do you think this reading will be about? Read the text and define its main idea.
Laser is an acronym for light amplification by stimulated emission of radiation. Lasers are devices that amplify light and produce coherent light beams, ranging from infrared to ultraviolet. A light beam is coherent when its waves, or photons, propagate in step with one another. Laser light, therefore, can be made extremely intense, highly directional, and very pure in color. Laser devices now extend into the X-ray frequency range. Based on the laser medium used, lasers are generally classified as solid state, gas, semiconductor, or liquid.
Lasers have become valuable tools in industry, scientific research, communication, medicine, the military, and the arts.
Powerful laser beams can be focused on a small spot with enormous power density. Consequently, the focused beams can readily heat, melt, or vaporize material in a precise manner. Lasers have been used, for example, to drill holes in diamonds, to shape machine-tools, to heat-treat semiconductor chips, to synthesize new material. The powerful short laser pulse also makes possible high-speed photography with an exposure time of several trillionths of a second.
They are also the most effective detectors of certain types of air pollution. In addition, lasers have been used for precise determination of the earth-moon distance and in tests of relativity. Very fast laser-activated switches are being developed for use in particle accelerators, and techniques have been found for using laser beams to slow down atoms for extremely precise studies of their spectra.
Because laser light is highly directional and monochromatic, extremely small amounts of light scattering or small frequency shifts caused by matter can easily be detected. By measuring such changes, scientists have successfully studied molecular structures of matter. With lasers, the speed of light has been determined to an unprecedented accuracy, chemical reactions can be selectively induced, and the existence of trace substances in samples can be detected.
Laser light can travel a large distance in outer space with little reduction in signal strength. Because of its high frequency, laser light can carry, for example, 1,000 times the television channels today carried by microwaves. Lasers are therefore ideal for space communications. Low-loss optical fibers have been developed to transmit laser light for earthbound communication in telephone and computer systems. Laser techniques have also been used for high-density information recording. For instance, laser light simplifies the recording of a hologram, from which a three-dimensional image can be reconstructed with a laser beam. Lasers are also used to play audio CDs and videodiscs.
Intense, narrow beams of laser light can cut and cauterize certain tissues in a small fraction of a second without damaging the surrounding healthy tissues. They have been used to "weld" the retina, bore holes in the skull, vaporize lesions, and cauterize blood vessels. Laser techniques have also been developed for lab tests of small biological samples.
Laser guidance systems for missiles, aircraft, and satellites have been constructed. The use of laser beams has been proposed against hostile ballistic missiles.
II. Read the text again carefully and answer the questions.
1. What is a laser?
2. When is a light beam coherent?
3. How are lasers generally classified?
4. Where have lasers become valuable tools?
5. What does the powerful short laser pulse make possible?
6. What are very fast laser-activated switches being developed for?
7. Why can extremely small amounts of light scattering be easily detected?
8. Can laser light travel a large distance in outer space?
9. What are lasers ideal for?
10. What has been developed to transmit light for earthbound communication in telephone and computer systems?
11. Where have lasers been used?
12. What does laser light simplify?
13. Are lasers used to play audio CDs and videodisks?
14. How are lasers used in medicine?
15. What has been proposed against hostile ballistic missiles?
III. Which of the vocabulary units used in paragraphs 1 could be regarded as scientific terms?
Amplification, classify, semiconductor, colour, step, photon, coherent light beams, use, range, emission, make, pure, solid state, extend, frequency, base.
IV. Read the translation of the forth paragraph. Compare it with the original and say if everything is right.
Οʜᴎ также являются более эффективными детекторами некоторых типов загрязнения воздуха. Дополнительно лазеры используются для точного определения расстояния между Луной и Землей и в тестах относительности. Разрабатываются очень быстрые переключатели, управляемые лазерным лучом, для использования в ускорителях частиц, а также были найдены технологии для использования лазерных пучков с целью замедления атомов для очень точных исследований их спектров.
V. Find the English equivalents of the following words and word combinations in paragraph 6.
Уменьшение, уровень сигнала, из-за, частота͵ канал, микроволны, связь, оптоволокно с малыми потерями, передавать, связь с Землей, запись информации, высокая плотность, к примеру, упрощать, объемное изображение, пучок, использовать.
VI. Find passage about the use of lasers in communication and translate it into Russian.
VII. Choose a passage and read it aloud (1-2 minutes).
VIII. Find complex grammar structures in the text and divide them into simple ones.
IX. Find out the subject-matter and the means of its secondary expression.
X. Find the topic sentences, key words and phrases which express the general meaning of each paragraph best of all.
XI. Using the information obtained in the paragraphs make a plan of the text.
XII. Speak about lasers using key words, phrases, the topic sentences and the plan of the text.
I. Look at the title of the text. Make your predictions about the contents of it. Read the text and answer the questions.
a .When do the electrons begin to move through conductors?
b .What are two main types of current?
c. What is the frequency of current?