UNIT 15

 

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

 

to constitute, frequency, to identify, to exhibit, reflection, refraction, dispersion, opaque, to encounter, matte, to absorb, to obtain, surface, concave, convex, the angle of incidence, image

 

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

 

Text: “Light and Reflection”.

 

Visible light constitutes only a very small part of the electromagnetic spectrum of wavelengths, just over a hundred-thousandth of an inch long. The longest visible wavelengths (lowest frequencies) are seen as red light, the shortest (highest frequencies) as violet. Various other colors can be identified between these two extremes. Conventionally, the spectral colors are red, orange, yellow, green, blue, indigo, and violet.

Being a form of electromagnetic radiation, visible light exhibits all the properties characteristic of such radiation – for example, wave-particle (photon) duality, reflection, refraction, diffraction, dispersion, interference, and polarization.

Light waves travel outwards in all directions from their source, thereby forming an expanding spherical wavefront. Each individual wave travels in a straight line in a vacuum, or in any isotropic medium (one with uniform properties throughout).

As light travels in straight lines, shadows are formed behind opaque objects. If the light source is very small, effectively a point source, the entire shadow is equally dark and has well-defined edges. If, on the other hand, the source is relatively large – which is usually the case – the shadow is blurred at the edges and has a dark central region of complete shadow (called the umbra) surrounded by a region of partial shadow (the penumbra), which is illuminated by light from part of the source.

Reflection. All objects and surfaces encountered in everyday life reflect light. That is why they are visible. Only a perfectly matte, black surface absorbs all light, and such a surface is extremely difficult to obtain. Many surfaces reflect only light of certain wavelengths, and so they appear colored when illuminated with light, which contains all visible wavelengths.

The nature of the surface also affects the type of reflection. Irregular surfaces and smooth, matte ones reflect light randomly and so cannot form images. For example, the pages of the book reflect light randomly, so enabling the type to be read rather than reflecting an image of the reader. Very smooth, shiny surfaces on the other hand, reflect light in a regular way and these types of  “mirror” surfaces can therefore form well-defined images.

Mirrors and images. There are three main types of mirrors: plane, concave, and convex. Plane mirrors are flat and are the most familiar type. Concave mirrors are hollowed – shaving mirrors are an example. And convex mirrors bulge outwards – they are used for some driving mirrors, for instance, because they give a wide angle of view.

Reflection in all three types of mirrors is governed by two principal laws. The first law of reflection states that the incident ray (or beam) striking the surface and the reflected ray (or beam) leaving it are in the same plane as the normal (an imaginary line perpendicular to the surface at the point where the incident ray hits it). The second law of reflection states that the angle of incidence (between the incident ray, or beam, and the normal) is equal to the angle of reflection (between the reflected ray, or beam, and the normal).

Using these two laws it is possible to determine the types of images formed by the different sorts of mirrors. 

 

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

 

1. The surface of still water can act as an almost perfect mirror.
2. In fact, the only difference among images formed by a convex mirror is their degree of diminution.
3. The farther the object is from the mirror, the smaller is the image.
4. The spectral colors are red, orange, yellow, green, blue, indigo and violet.
5. The nature of the surface also affects the type of reflection.
6. As the object is moved nearer the mirror, the image becomes larger.
7. Moving the object just inside the focus produces an upright, much magnified virtual image.
8. The image formed by a plane mirror is the same size as the object.

 

IV. Find English equivalents in the text.

 

1. самые низкие частоты _______________________________________
2. фиолетовый ________________________________________________
3. обычно ____________________________________________________
4. будучи одной из форм электромагнитного излучения ___________
5. поглощать свет _____________________________________________
6. содержать все видимые длины волн ___________________________
7. гладкие, матовые поверхности ________________________________
8. формировать четкие изображения ____________________________
9. тень _______________________________________________________
10. полутень ___________________________________________________
11. выпуклое зеркало ___________________________________________
12. вогнутое зеркало ____________________________________________
13. закон гласит ________________________________________________
14. угол падения равен углу отражения ___________________________

 

V. Find Russian equivalents to the following expression in the text.

 

1. electromagnetic spectrum of wave lengths ___________________________
2. to exhibit the properties __________________________________________
3. diffraction _____________________________________________________
4. all surfaces encountered in everyday life _____________________________
5. they appear coloured when illuminated ______________________________
6. irregular surfaces _______________________________________________
7. to reflect light randomly __________________________________________
8. to reflect light in a regular way ____________________________________
9. well-defined images _____________________________________________
10. plane mirrors __________________________________________________
11. the incident ray _________________________________________________
12. to determine the types of images ___________________________________

 

VI. Fill in the missing words.

 

1. Visible light constitutes only a very small part of the _______ _______ of wavelengths.
2. Conventionally, the spectral colours are listed as red, orange, _______, _______, _______, _______ and violet.
3. Visible light exhibits all the _______ characteristic of electromagnetic radiation.
4. All objects and surfaces _______ in everyday life _______ light.
5. Only a perfectly matte, black surface _______ all light.
6. The nature of the surface _______ the type of reflection.
7. Irregular surfaces reflect light _______.
8. Very smooth, shiny surfaces reflect light _______.
9. There are three main types of mirrors: _______.
10. Reflection in all three types of mirrors _______ by two principal laws.
11. The first law of reflection states that the incident ray _______ the surface and the reflected ray _______ it are in the same plane as the normal.
12. The second law of reflection states that _______ is equal to the angle of reflection.

 

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.

 

XII. Dictation-translation.

 

1. Углы падения и отражения увеличиваются, т.к. чем больше углы, тем меньше света преломляется и больше отражается.
2. Самая большая длина волны, с самой низкой частотностью видна как красный свет.
3. Самая короткая длина волны с самой высокой частотностью видна как фиолетовый свет.
4. Так как свет проходит по прямым линиям, позади светонепроницаемого предмета образуется тень.
5. Все предметы и поверхности отражают свет, и поэтому они видны.
6. Темная поверхность поглощает свет.
7. Очень гладкие светлые поверхности отражают свет.
8. Существует три типа зеркал: плоское, вогнутое и выпуклое.
9. Нормаль – это воображаемая линия, перпендикулярная поверхности в той точке, где падающий луч касается её.
10. Угол падения равен углу отражения.