Read the text about general features and properties of lasers. Choose the best answer a, b or c.1.The word ‘laser’ is an acronym derived from … a. low amplification by the strong emission of radiation’ b. light amplification by the stimulated emission of radiation’ c. low amplification by the stimulated emission of radiation’ 2.Lasers are devices that are adapted to: a. medium wavelengths of light b. shorter wavelengths of light c. longer wavelengths of light 3. Lasers operate in: a. the ultraviolet regions of the spectrum b. the infrared regions of the spectrum c. the infrared, visible or ultraviolet regions of the spectrum 4. Laser radiation is emitted … a. through a spontaneous process b. through the process of disintegration c. by the process of stimulated emission 5. An active medium may be … a. liquid b. solid c. gaseous, solid or liquid 6. The reflecting surfaces of the mirrors are specially coated, with alternate layers of … a. low dielectric materials b. high dielectric materials c. high and low dielectric materials 7. Photons are generated initially … a. in the mirror b. in the cavity c. in the dielectric materials
8.Laser is now used… a. in guiding missiles b. in welding transistor junctions c. in punching holes in sheets of metal.
9.There are suggestions that laser beams… a. can flip a plane and toss it out of control; b.can replace cables in telecommunications; c. can pass through a lens system. 10. Lasers opened a whole new area of: a. mechanics b. optics c. electromagnetism
19 .Read the text about general features and properties of lasers and answer the following questions.
1. What is a laser? 2. Who invented a laser? 3. When was a laser invented? 4. What is the difference between a maser and a laser? 5. What is the main principle of work of a laser? 6. What material is used as an active medium of a laser? 7. Where can a laser beam be used? 8. What quality of a laser is being exploited as its military potential? 20. There is one mistake in each of the following sentences. Find it and correct it.
1. Lasers have been invented in 1970. 2. It is impossible to produce a powerful beam of light with the help of a laser. 3. Having invented a laser man did not find possibilities for its application. 4. There is just one type of a maser or a laser. 5. The scientists now cannot think of complete new applications of lasers. 6. A laser can not be used as a means of cancer treatment. 7. Masers are used in making holograms. 8. Laser radiation has three very remarkable properties.
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