|
Читайте также: |
1. Visible a) electron
2. Triangular b) void
3. Optical c) light
4. Transparent d) frequency
5. Interatomic e) prism
6. Absorbed f) materials
7. Vibrating g) density
8. Resonant h) energy
Exercise 46. Insert some word-combinations from exercise 45.
1. A ______________ disperses the light into seven colors: red, orange, yellow, green, blue, indigo and violet.
2. _______________ in a spectrum is composed of different colors.
3. ________________ allow light pass through it.
4. The ________________ causes the electrons in the atom to vibrate.
5. The speed of the transmitting electromagnetic wave depends upon the _______________ of that particular material through which it passes.
6. Materials with higher index of refraction values hold onto the absorbed light energy for greater lengths of time before reemitting it to the __________________.
Exercise 47. In pairs, do the following quiz.
QUIZ “Dispersion of light”
1. How are the colors of the rainbow formed?
a) From the sun hitting water.
b) From light hitting objects.
c) Through different wavelengths of refracted light.
2.When does a rainbow occur in nature?
a) After a snowstorm. b) After a rainstorm, when the sun comes out.
3) Which colors of the rainbow have the longest wavelengths?
a) Violet b) Orange c) Yellow d) Indigo e) Red
4. Rainbows are just straight lines across the sky.
a) No, they are full circles. b) They are a half crescent.
5. What causes light to refract off of certain objects?
a) When the beam of light goes through the object, the light bounces off, because the light is pointed at an angle.
b) The object is not transparent.
c) The object is transparent.
6. Which color has a shorter wavelength: green or orange?
a) Green b) Orange c) Both colors have the same wavelength
7. Can you see a rainbow when facing the Sun?
a) Not if the Sun is too bright
b) There are no rainbows if the Sun is shining
c) The Sun must be behind you
Exercise 48. Read the text and complete it with clauses a–e.
a) scattered in all directions
b) allowing the reds and yellows
c) What Makes a Red Sunset?
d) fades to a lighter blue or white
e) other light travels in long waves
f) the surface of Earth
Why is the sky blue?
The light from the Sun looks white. But it is really made up of all the colors of the rainbow. Like energy passing through the ocean, light energy travels in waves, too. Some light travels in short waves but 1)_____. Blue light waves are shorter than red light waves. All light travels in a straight line unless something gets in the way to reflect it (like a mirror), bend it (like a prism) or scatter it (like molecules of the gases in the atmosphere). Sunlight reaches Earth's atmosphere and is scattered in all directions by all the gases and particles in the air. Blue light is 2)____ by the tiny molecules of air in Earth's atmosphere. Blue is scattered more than other colors because it travels as shorter, smaller waves. This is why we see a blue sky most of the time. Closer to the horizon, the sky 3)_____. The sunlight reaching us from low in the sky has passed through even more air than the sunlight reaching us from overhead. As the sunlight has passed through all this air, the air molecules have scattered and rescattered the blue light many times in many directions. Also, 4)_____ has reflected and scattered the light. All this scattering mixes the colors together again so we see more white and less blue.
5)__________________
As the Sun gets lower in the sky, its light is passing through more of the atmosphere to reach you. Even more of the blue light is scattered, 6) ______ to pass straight through to your eyes.
Grammar. Participle.
Exercise 49. a) Fill in the correct participle.
Paul: You must be 1) ___________(thrill). Paris is a 2) __________ (fascinate) city. There are so many 3) ___________ (interest) things to do. Youwon't be 4) ___________ (bore).
Jane: Well, I'm a bit 5) __________ (worry) because I can't speak French very well. People will find my accent very 6) ____________ (amuse).
Paul: Don't be silly! I'm sure you'll have an 7) __________.(excite) time.
Exercise 50. Translate the following sentences into English using Participle.
1. Читаючи англійські книги, вона завжди виписує нові слова. 2. Студенти, які працюють у нашому офісі, приїхали зі Львову. 3. Сказавши це, вони припинили розмову. 4. Оскільки її вже запросили на вечірку, вона не змогла піти з нами в театр. 5. Після того, як посилку запакували, її віднесли на пошту. 6. Читаючи ці листи, вона згадала своє дитинство. 7. Не знаючи дороги, вона не могла йти швидко. 8. Повторюючи вірш багато разів, ви можете вивчити його. 9. Будьте обережні, переходячи вулицю. 10. Він поранив руку, граючи в теніс. 11. Діставши ключ з кишені, він відкрив двері.
Writing
Exercise 51. Translate the sentences into English using active vocabulary.
1. Дисперсія світла – це явище залежності абсолютного показника заломлення світла речовиною від частоти світла, що падає на речовину (або від довжини хвилі у вакуумі). 2. Дисперсія виникає внаслідок взаємодії світла з речовиною. 3. Показник заломлення світла пов'язаний із швидкістю поширення світла в речовині. 4. Чим більша довжина хвилі, тим більша швидкість її поширення у середовищі. 5. Отже, з найбільшою швидкістю поширюються хвилі, які ми сприймаємо як червоне світло, а найменшою – хвилі, які ми сприймаємо як фіолетове світло. 6. Проявом дисперсії є розкладання призмою білого світла у спектр. 7. Хвилі, які входять до складу білого світла, поширюються з різними швидкостями в речовині. 8. Проходячи через призму, складові частини білого променя зазнають різного заломлення і відображаються у вигляді спектра.
Unit 5. Interference and Diffraction.
Active vocabulary
1. Acoustic impedance акустичний імпеданс,
[ə'kuːstɪk ɪm'piːd(ə)ns] акустичний опір (повний)
2. Brightness ['braɪtnɪs] яскравість
3. Constructive interference конструктивна інтерференція
[kən'strʌktɪvˌɪntə'fɪərəns]
4. Corona [kə'rəunə] сонячна корона (при повному затемненні), кільце (навколо місяця)
5. (To) deflect [dɪ'flekt] відхиляти(ся)
6. Destructive interference деструктивна інтерференція
[dɪs'trʌktɪvˌɪntə'fɪərəns]
7. Diffraction [dɪ'frækʃ(ə)n] дифракція
8. Diffraction grating [dɪ'frækʃn'greɪtɪŋ] дифракційна ґратка
9. (To) disperse [dɪs'pɜːs] розсіювати
10. Fringe [frɪnʤ] край, межа, грань
11. Huygens–Fresnel principle принцип Гюйгенса-Френеля
['haɪgənz fre(ɪ)'nel'prɪnsəpl]
12. Interference [ɪntə'fɪərəns] інтерференція
13. Monochromatic light монохроматичне світло
[ˌmɔnəkrə'mætɪk'laɪt]
14. Naked eye ['neɪkɪdˌaɪ] неозброєне око
15. Secondary wave ['sekəndərɪˌweɪv] вторинна хвиля
16. Silver lining ['sɪlvə'laɪnɪŋ] срібляста кромка (хмари)
17. Speckle pattern ['spek(ə)lˌpætn] спекл-структура
18. Spectrometer [spek'trɔmɪtə] спектрометр
19. Superposition [ˌs(j)uːpəpə'zɪʃ(ə)n] суперпозиція, накладення
Reading
Exercise 52. Read, translate the text below.
DIFFRACTION
Diffraction refers to various phenomena which occur when a wave encounters an obstacle. Italian scientist Francesco Maria Grimaldi coined the word ‘diffraction’ and was the first to record accurate observations of the phenomenon in 1665. The diffraction phenomenon is described as the apparent bending of waves around small obstacles and the spreading out of waves past small openings. Similar effects occur when light waves travel through a medium with a varying refractive index or a sound wave through one with varying acoustic impedance. Diffraction occurs with all waves, including sound waves, water waves, and electromagnetic waves such as visible light, x-rays and radio waves.
Thus, diffraction is the slight bending of light as it passes around the edge of an object. The amount of bending depends on the relative size of the wavelength of light to the size of the opening. If the opening is much larger than the light's wavelength, the bending will be almost unnoticeable. However, if the two are closer in size or equal, the amount of bending is considerable, and easily seen with the naked eye.
Fig. 6.12.
|
While diffraction occurs whenever propagating waves encounter such changes, its effects are generally most pronounced for waves where the wavelength is on the order of the size of the diffracting objects. If the obstructing object provides multiple openings, a complex pattern of varying intensity can result. This is due to the superposition, or interference, of different parts of a wave that traveled to the observer by different paths.
Optical effects resulting from diffraction are produced through the interference of light waves. To visualize this, imagine light waves as water waves. If water waves were incident upon a float residing on the water surface, the float would bounce up and down in response to the incident waves, producing waves of its own. As these waves spread outward in all directions from the float, they interact with other water waves. If the crests of two waves combine, an amplified wave is produced (constructive interference). However, if a crest of one wave and a trough of another wave combine, they cancel each other out to produce no vertical displacement (destructive interference).
This concept also applies to light waves. When sunlight (or moonlight) encounters a cloud droplet, light waves are altered and interact with one another in a similar manner as the water waves described above. If there is constructive interference (the crests of two light waves combining), the light will appear brighter. If there is destructive interference (the trough of one light wave meeting the crest of another), the light will either appear darker or disappear entirely.
The effects of diffraction are often seen in everyday life. The most striking examples of diffraction are those involving light; for example, the closely spaced tracks on a CD or DVD act as a diffraction grating to form the familiar rainbow pattern seen when looking at a disk. This principle can be extended to engineer a grating with a structure such that it will produce any diffraction pattern desired; the hologram on a credit card is an example. Diffraction in the atmosphere by small particles can cause a bright ring to be visible around a bright light source like the sun or the moon. A shadow of a solid object, using light from a compact source, shows small fringes near its edges. The speckle pattern which is observed when laser light falls on an optically rough surface is also a diffraction phenomenon. All these effects are a consequence of the fact that light propagates as a wave.
Diffraction can occur with any kind of wave. Ocean waves diffract around jetties and other obstacles. Sound waves can diffract around objects, which is why one can still hear someone calling even when hiding behind a tree. Diffraction can also be a concern in some technical applications; it sets a fundamental limit to the resolution of a camera, telescope, or microscope.
Diffraction arises because of the way in which waves propagate; this is described by the Huygens–Fresnel principle. The propagation of a wave can be visualized by considering every point on a wavefront as a point source for a secondary radial wave. The subsequent propagation and addition of all these radial waves form the new wavefront. When waves are added together, their sum is determined by the relative phases as well as the amplitudes of the individual waves, an effect which is often known as wave interference. The summed amplitude of the waves can have any value between zero and the sum of the individual amplitudes. Hence, diffraction patterns usually have a series of maxima and minima (http://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/opt/mch/diff.rxml).
Exercise 53. Match the lines in A to their definitions in B, and give their Ukrainian equivalents.
| A | B | Ukrainian Equivalent |
| 1. Diffraction grating | a) The variation of wave amplitude that occurs when waves of the same or different frequency come together. | |
| 2. Monochro-matic light | b) The ratio of the velocity of light in a vacuum to its velocity in a specified medium. | |
| 3. Destructive interference | c) Unassisted vision, without a telescope, microscope or other device. | |
| 4. Diffraction | d) A plate of glass or metal ruled with very close parallel lines, producing a spectrum by diffraction and interference of light. | |
| 5. Construc-tive interference | e) The ratio of the pressure over an imaginary surface in a sound wave to the rate of particle flow across the surface. | |
| 6. Spectro-meter | f) Any bending of wave by means other than reflection or refraction. | |
| 7. Acoustic impedance | g) Light of one color. | |
| 8. Refractive index | h) When the crest of one wave overlaps the crest of another, there individual effects add together. | |
| 9. Interfe-rence | i) When the crest of one wave overlaps the trough of another, their individual effects are reduced. | |
| 10. Naked eye | j) A spectroscope equipped with scales for measuring wavelengths or indexes of refraction. |
Exercise 54. In the text above find words to complete the following groups of synonyms.
1. meet, collide, _________
2. create, make, generate, _________
3. obstruction, hindrance, barrier, ____________
4. repeated, frequent, manifold, _____________
5. devise, create, contrive, _____________
6. follow (from), ensue, _____________
7. changing, fluctuating, _____________
8. border, brim, brink, boundary, ____________
Exercise 55. Answer the questions to the text.
1. What is diffraction?
2. Who devised the term ‘diffraction’?
3. What examples of light diffraction can you give?
4. What is interference? What example of interference can you give?
5. What types of interference do you know?
6. What does the Huygens–Fresnel principle state?
Exercise 56. A) Fill in the blanks with the words and word combinations from the box.
| colours monochromatic light Huygens interference prisms diffraction gratingwave natureThomas Young |
Young’s Interference Experiment
Young’s interference experiment demonstrated the ________ of light originally proposed by _________.
In 1801 the British physicist and physician _____________ discovered that when ________________– light from a single colour –was directed through two closely spaced pinholes, fringes of brightness and darkness were produced on a screen behind. A multitude of closely spaced parallel slits makes up what is called _______________.
Many spectrometers use diffraction gratings rather than _________ to disperse light into _________. Whereas a prism separates the colours of light by refraction, a diffraction grating separates colours by _____________.
B) Here are the answers to the text above. Reconstruct the wh-questions.
1. the wave nature of light
2. in 1801
3. diffraction grating
4. to disperse light into colours
5. by interference
Exercise 57. Indicate whether the sentence or statement is true or false. If false, change it to make the statement true.
1. You can hear sounds around the corner of a door due to the wave property called diffraction.
2. Diffraction gratings provide much brighter interference patterns since more light passes through them compared with double slits.
3. When white light passes through a diffraction grating, red light is deflected least.
4. CDs use the principles of thin film interference and polarization.
5. When light passes from one medium to another with a different refractive index, diffraction occurs.
Speaking
Exercise 58. Explain the following terms in your own words.
Reflection Dispersion Refractive index
Refraction Interference Monochromatic light
Dispersion Prism Angle of deviation
Дата добавления: 2015-10-29; просмотров: 300 | Нарушение авторских прав
| <== предыдущая страница | | | следующая страница ==> |
| DISPERSION OF LIGHT BY PRISMS | | | Grammar. Participle. |