I. Find out the words in the dictionary. Write them down and learn

VII. Fill in the prepositions, if necessary.

1. Many surfaces appear coloured when illuminated ___ light.

2. The nature ___ the surface affects the type of reflection.

3. Very smooth surfaces ___ the other hand reflect light ___ a regular way.

4. Reflection ___ all three types of mirrors is governed ___ two principal laws.

5. The angle ___ incidence is equal ___ the angle of reflection.

6. Using this two laws it is possible to determine the types of images formed ___ the different sorts ___ mirrors.

7. The type of image formed by a concave mirrors depends ___ the distance ___ the object and mirrors.

VIII. Define whether the sentences are true or false.

1. Visible light constitutes a very large part of the electromagnetic spectrum of wavelengths.

2. The spectral colours are listed as white, red, orange, yellow, green, blue, indigo, and violet.

3. Visible light exhibits all the properties characteristic of electromagnetic radiation.

4. A perfectly matte, black surface reflects all light.

5. The nature of the surface affects the type of reflection.

6. Very smooth, shiny surfaces reflect light randomly.

7. There are two main types of mirrors: concave and convex.

8. Reflection in all types of mirrors is governed by four principal laws.

IX. Practice with someone asking and answering.

1. What part of the electromagnetic spectrum of wavelengths does visible light constitute?

2. How are the longest and the shortest visible wavelengths seen?

3. How can various other colours be identified?

4. How are the spectral colour listed?

5. What properties does visible light exhibit?

6. Why are the objects and surface encountered in everyday life visible?

7. What surface absorbs all light?

8. What affects the type of reflection?

9. How do irregular surfaces reflect light?

10. How do very smooth and shiny surfaces reflect light?

11. How many types of mirrors are there?

12. What is the reflection in all three types of mirrors governed by?

13. What does the first law of reflection state?

14. What does the second law of reflection state?

X. Put questions to the following sentences.

1. Irregular surfaces reflect light randomly.

2. There are three main types of mirrors.

3. Reflection in all types of mirrors is governed by two principal laws.

4. Visible light exhibits all the properties characteristic of electromagnetic radiation.

5. All objects and surfaces encountered in everyday life reflect light.

6. Many surfaces reflect only light of certain wavelengths.

7. The image formed by a plane mirror is the same size as the object.

XI. Dictate the following sentences in English to your fellow-students. Check them together.

1. Visible light constitutes only a very small part of the electromagnetic spectrum of wavelengths.

2. Visible light exhibits all the properties characteristic of such radiation – wave particle duality, reflection, refraction, diffraction, dispersion, interference and polarization.

3. The nature of the surface also affects the type of reflection.

4. The incident ray (or beam) striking the surface and the reflected ray (or beam) leaving it are in the same plane as the normal.

5. The angle of incidence is equal to the angle of reflection.

UNIT 16

I. Find out the words in the dictionary. Write them down and learn.

a filament, incandescence, a source, to emit, to acquire, to de-

cay, ground state, excited state, a light range, to derive, to persist,

excitation, steady, removal, to diminish, vapor, coherent, incoherent

II. Read the text. Use a dictionary, if necessary.

TEXT: «LUMINESCENCE»

Nearly all light-emitters are extremely hot; examples include the sun and other stars, the filament of an electric lamp, and a candle flame. In physical terms they are all incandescent light sources. But there is another smaller group of «cold» sources that emit light by the phenomenon of luminescence. Fluorescent lamps and the luminescent numerals on a clock, which glow in the dark are examples. And a third type of light source – also not incandescent – is the laser. Both incandescence and luminescence have the same fundamental origin, which results from energy changes within the atoms of the radiating object. Electrons within the atoms acquire energy, are «excited» to higher energy levels, and in decaying again to their ground states emit electromagnetic radiation in the visible light range. In an incandescent object, the exciting energy is externally applied heat; in a luminescent object, it derives from within the object itself or from an external source other than heat. There are two kinds of luminescence. The type that ceases when external excitation stops is known as fluorescence; the type, that persists even in the absence of external excitation, is called phosphorescence. Certain bacteria and some minerals and organic chemical compounds that readily glow when irradiated by ultraviolet light are examples of fluorescence. Some washing powders contain fluorescent compounds called optical brighteners that make fabrics appear brighter and cleaner. The cold, steady light given off by certain fungi is an example of phosphorescence: it persists after the removal of the initial stimulus. An inorganic example is the glow of one type of luminous paint, for which the energy source is daylight, which is re-emitted as green light, the glow fading as the «stored» energy diminishes. Incoherent and coherent light. In a fluorescent lamp, atoms of mercury vapor are bombarded by electrons and emit ultraviolet light. This radiation in turn excites a phosphor coating inside the tube that emits visible light. But not all the mercury atoms are hit by electrons at the same instant. Thus, some are in an excited state while others are in the ground state. The overall light output is therefore a randomly discontinuous series of extremely brief pulses. This kind of light, which is also produced by all normal incandescent sources, is said to be incoherent. Waves of light from two such sources do not stay in phase (in step) with each other for any length of time. Where they meet, they cannot, therefore, produce the regular pattern of intensification and extinction that is typical of what is called the interference of light waves, even though the wavelengths may be more or less identical and the light thus monochromatic. An interference pattern results when two sources emit light of the same wavelength and in phase; such light is called coherent. It is produced, by a process similar to fluorescence, in a laser – a name that denotes Light Amplification by Stimulated Emission of Radiation. Stimulated emission can be best understood by considering light as a stream of electromagnetic radiation particles (photons).

III. Find a verb in each line and translate it. Translate also the underlined words.

a) Relatively, opaque, encounter, uncertain, image;

b) Straight, conventionally, matte, surface, obtain;

c) Identify, randomly, angle, irregular, mirror;

d) Invisible, interference, constitute, equally, refraction;

e) Reflection, perfectly, wavelength, unfamiliar, disappear;

f) Absorb, spectrum, incomplete, extremely, incidence.

IV. Find the sentences that can’t be found in the text.

1. There is another smaller group of «cold» sources that emit light by the phenomenon of luminescence.

2. Every source of light is known to have a luminous intensity, which is measurable.

3. In an incandescent object, the exciting energy is externally applied heat; in a luminescent object, it derives from within the object itself or from an external source other than heat.

4. This radiation in turn excites a phosphor coating inside the tube that emits visible light.

5. The overall light output is therefore a randomly discontinuous series of extremely brief pulses.

6. Incandescence is the emission of light caused by high temperatures.

7. The luminescent substance absorbs the energy and the re-radiation may be immediate, so that excitation and luminescence coincide in time.

8. An interference pattern results when two sources emit light of the same wavelength and in phase; such light is called coherent.

VI. Find Uzbek equivalents to the following expressions in the text.

1. light-emitters ________________________________________

2. are extremely hot ______________________________________

3. incandescent light sources _______________________________

4. the same fundamental origin ___________________________

5. results from _________________________________________

6. the radiating object ____________________________________

7. electrons within the atoms ______________________________

8. higher energy level ____________________________________

9. in decaying to their ground states _________________________

10. emit electromagnetic radiation in the visible light range _______

11. an external source other than heat ________________________

12. excitation _________________________________________

13. organic chemical compounds __________________________

14. when irradiated by ultraviolet light ______________________

15. atoms of mercury vapor________________________________

16. are bombarded by electrons _____________________________

17. a phosphor coating __________________________________

18. at the same instance __________________________________

19. do not stay in phase ___________________________________

VII. Analyse the structure of the following sentences.

1. Electrons within the atoms acquire energy, are «excited» to higher energy levels, and in decaying again to their ground states emit electromagnetic radiation in the visible light range.

2. Certain bacteria and some minerals and organic chemical com pounds that readily glow when irradiated by ultraviolet light are examples of fluorescence.

3. The type that ceases when external excitation stops is known as fluorescence.

4. An inorganic example is the glow of one type of luminous paint, for which the energy source is daylight, which is re-emitted as green light, the glow fading as the «stored» energy diminishes.

VIII. Fill in the missing words.

1. Nearly all light-emitters are extremely hot; examples _______ the sun and other stars, the filament of an electric lamp, and a candle light.

2. In physical terms they are all _______ light sources.

3. Fluorescent lamps and the luminescent numerals on a clock, which _______ in the dark are examples.

4. Both incandescence and luminescence have the same fundamental _______, which results from energy _______ within the atoms of the radiating object.

5. In a luminescent object the exciting energy derives from within the object itself or from _______ source other than heat.

6. The type of luminescence that ______ when external excitation, is called _____.

7. The overall light _______ is a randomly ______ series of extremely brief pulses.

8. This kind of light, which is also produced by all normal _______ sources, is said to be ________.

9. Waves of light from two such sources do not stay in _______ with each other for any length of time.

10. Stimulated _______ can be best understood by considering light as a _______ of electromagnetic radiation particles.

IX. Fill in the prepositions, if necessary.

1. Fluorescent lamps and luminescent numerals ___ a clock, which glow ___ the dark are examples.

2. Both incandescence and luminescence have the same fundamental origin, which results ___ energy changes ___ the atoms ___ the radiating object.

3. In a luminescent object the exciting energy derives ___ ___ the object itself or ___ an external source other than heat.

4. Certain bacteria and some minerals and organic chemical compounds that readily glow when irradiated ___ ultraviolet light are examples of fluorescence.

5. ___ a fluorescent lamp, atoms ___ mercury vapor are bombarded ___ electrons and emit ultraviolet light.

6. But not all the mercury atoms are hit ___ electrons ___ the same instant.

7. Waves ___ light ___ two such sources do not stay ___ phase ___ each other ___ any length ___ time.

8. Stimulated emission can be best understood ___ considering light as a stream ___ electromagnetic radiation particles.

X. Define whether the sentences are true or false.

1. Nearly all light-emitters are extremely cold.

2. There is another smaller group of «cold» sources that emit light by the phenomenon of luminescence.

3. And a third type of light source – also incandescent – is the laser.

4. In an incandescent object, the exciting energy derives from within the object itself or from an external source other than heat.

5. There are three kinds of luminescence.

6. The type that ceases when external excitation stops is known as fluorescence; the type that persists even in the absence of external excitation, is called phosphorescence.

7. In a fluorescent lamp, atoms of mercury vapor are bombarded by electrons and emit infrared light.

8. All the mercury atoms are hit by electrons at the same instant.

9. An interference pattern results when two sources emit light of the same wavelength and in phase; such light is called coherent.

XI. Answer the question.

1. Are all light-emitters extremely hot or cold?

2. What are the examples of hot light-emitters?

3. How are they called in physics?

4. There is also a group of «cold» sources. Is it larger or smaller?

5. In what way do «cold» sources emit light?

6. What are the examples of «cold» sources of light?

7. There is a third type of light source. What is it?

8. Do incandescence and luminescence have the same fundamental origin? What does it result from?

9. How do electrons behave in an atom?

10. What is the source of the exciting energy in an incandescent object? And where does the exciting energy derive from in a luminescent object?

11. Are there two or three kinds of luminescent? What are they?

12. What are the examples of fluorescence?

13. What compounds do some washing powders contain?

14. What are the organic and inorganic examples of phosphores cence?

XII. Put questions to the following sentences.

1. Both incandescence and luminescence have the same fundamental origin. (General)

2. In an incandescent object the exciting energy is externally applied heat. (Alternative)

3. There are two kinds of luminescence. (Disjunctive)

4. This radiation in turn excites a phosphor coating inside the tube. (Special)

5. An interference pattern results when two sources emit light of the same wavelength and in phase. (Special)

XIII. Dictate the following sentences in English to your follow-students. Check them together.

1. Both incandescence and luminescence have the same fundamental origin, which results from energy changes within the atoms of the radiating object.

2. In an incandescent object, the exciting energy is externally applied heat.

3. In a luminescent object, it derives from within the object itself or from an external source other than heat.

4. In a fluorescent lamp, atoms of mercury vapor are bombarded by electrons and emit ultraviolet light.

5. The overall light output is therefore a randomly discontinuous series of extremely brief pulses.

6. An interference pattern results when two sources emit light of the same wavelength and in phase; such light is called coherent.

7. It is produced, by process similar to fluorescence, in a laser – a name that denotes Light Amplification by Stimulated Emission of Radiation.

UNIT 17

I. Find out the words in the dictionary. Write them down and learn.

to ionize, to penetrate, span, upward, reveal, potential, to ro-

tate, voltage, to insulate, shield, lead, cancer, ionic, concrete, flaw,

ultimate, thorium, to overlap

II. Read the text. Use a dictionary, if necessary.

TEXT: «X-RAYS AND GAMMA-RAYS»

The part of the electromagnetic spectrum with very short wavelengths (between about 10 -9 m and 10 -15 m) and very high frequencies corresponds to X-rays and gamma rays. Both are high-energy, penetrateing types of radiation that can ionize gases and cause other chemical and physical changes, such as fluorescence. X-rays. X-rays are one of the types of radiation emitted by some stars and galaxies. Studies of heavenly bodies from artificial satellites have revealed various X-ray sources, among which are possible locations of black holes. The observations have to be made from space because X-rays do not pass through the atmosphere (although highly energetic, X-rays do not penetrate the atmosphere because they interact with molecules in the air). Here on earth, X-rays are generated artificially. X-rays are produced using thermionic vacuum tubes that operate at potentials of up to 2 million volts. A stream of electrons, fired from the cathode of the tube, strikes a metal anode (the target), which emits X-rays. The X-ray beam is emitted at right angles to the electron beam. Because of the high voltage necessary and the penetrating power of the radiation itself, commercial X-ray machines are heavily insulated and shielded with lead, which absorbs X-ray. The best-known uses of X-rays are in medicine: in radiology to «photograph» the internal structures of the body and in radiotherapy for destroying cancerous tumors. X-rays are also used extensively for internal examination of industrial materials, for example in the detection of flaws and other weaknesses in metal castings and welds. Gammarays. During the radioactive decay of unstable isotopes of elements, such as uranium, thorium, and radium, gamma rays are emitted. These constitute electromagnetic radiation of extremely short wavelength, from about 10 -10 m down to 10 -15 m or less, overlapping to some extent with those of «hard» X-rays. The main difference between the two types of radiation is in their origins. X-rays are produced by bombardment of atoms with high-energy electrons, which cause excitation of the atomic electrons. Gamma-rays derive from the excitation of the atomic nucleus itself. In both cases, characteristic radiation is emitted when the excited electrons or nucleons return to their original energy levels. The properties of gamma-rays resemble those of X-rays. Like X-rays, gamma rays can be used to reveal flows in solid materials; a suitable source for such applications is cobalt-60 or some other long-lived radioisotope. In research into particle physics, gamma-rays often occur as product of collisions between high-energy subatomic particles. They are, therefore, important in the study of the ultimate structure of matter.

III. Find the sentences that can’t be found in the text.

1. X-rays are one of the types of radiation emitted by some stars and galaxies.

2. X-rays were found to produce strong ionization in gases.

3. X-rays are produced when the fast moving electrons of the cathode stream are suddenly stopped.

4. The X-ray beam is emitted at right angels to the electron beam.

5. The main difference between the two types of radiation is in their origins.

6. Gamma-rays do not carry a charge of electricity and are not deflected by either an electric or a magnetic field.

7. The properties of gamma-rays resemble those of X-rays.

V. Find Uzbek equivalents to the following expressions in the text.

1. the electromagnetic spectrum with very short wavelengths ______

2. penetrating types of radiation ____________________________

3. studies of heavenly bodies have revealed ___________________

4. are generated artificially ________________________________

5. at potentials of up to 2 million volts ________________________

6. is emitted at right angles ________________________________

7. are heavily insulated and shielded ________________________

8. the internal structures of the body _________________________

9. the detection of flaws __________________________________

10. overlapping to some extent _____________________________

11. high-energy electrons _________________________________

12. cause excitation of the atomic electrons ___________________

13. occur as a product of collision ___________________________

14. ultimate structure of matter _____________________________

VI. Analyze the structure of the sentence.

1. The observations have to be made from space because X-rays do not pass through the atmosphere.

2. X-rays are produced by bombardment of atoms with high-energy electrons, which cause excitation of the atomic electrons.

VII. Fill in the missing words.

1. The part of the electromagnetic spectrum with very short _____ and very high _____ corresponds to X-rays and gamma-rays.

2. Both are high-energy, penetrating types of radiation that can _____ gases and cause other chemical and physical changes, such as _____.

3. Studies of heavenly bodies from _____ _____ have revealed various X-ray _____.

4. Here on earth, X-rays are _____ artificially.

5. Commercial X-ray machines are heavily _____ and _____ with lead, which absorbs X-ray.

6. The main difference between the two types of radiation is in their _____.

7. Gamma-rays _____ from the excitation of the atomic nucleus itself.

8. Like X-rays, gamma-rays can be used to _____ flows in solid materials.

9. In research into particle physics, gamma rays often occur as product of _____ between high-energy subatomic particles.

VIII. Fill in the prepositions if necessary.

1. X-rays are one ___ the types ___ radiation emitted ___ some stars and galaxies.

2. The observations have to be made ___ space.

3. Here ___ earth, X-rays are generated artificially.

4. A stream ___ electrons, fired ___ the cathode ___ the tube, strikes ___ a metal anode, which emits X-rays.

5. The X-ray beam is emitted ___ right angles ___ the electron beam.

6. Because ___ the high voltage necessary and the penetrating power ___ the radiation itself, commercial X-ray machines are heavily insulated and shielded ___ lead.

7. X-rays are produced ___ bombardment ___ atoms ___ high energy electrons, which cause excitation ___ the atomic electrons.

8. Gamma-rays derive ___ the excitation ___ the atomic nucleus itself.

9. Like X-rays, gamma-rays can be used to reveal flows ___ solid

materials; a suitable source ___ such applications is cobalt-60 or some other long-lived radioisotope.

10. They are, therefore, important ___ the study ___ the ultimate structure ___ matter.

IX. Define whether the sentences are true or false.

1. X-rays and gamma-rays are high-energy, penetrating types of radiation that can ionize gases and cause other chemical and physical changes, such as fluorescence.

2. Studies of heavenly bodies from artificial satellites haven’t revealed any X-ray sources.

3. The X-ray beam is emitted at obtuse angles to the electron beam.

4. Because of the high voltage necessary and the penetrating power of the radiation itself, commercial X-ray machines are heavily insulated and shielded with lead, which absorbs X-rays.

5. The best-known uses of X-rays are in chemistry.

6. The main difference between the two types of radiation is in their properties.

7. In research into particle physics, gamma-rays often occur as product of collisions between low-energy subatomic particles.