Exercises

1. Learn the following definitions:

Polarizer is an instrumental means to produce polarized light.

Analyzer is an instrumental means which detects light polarization and dejection of vibrations.

Optical vector is an oscillation vector whose direction does not coincide with the option of propagation.

2. Translate the following sentences:

1. То, что интенсивность света зависит от углового положения второго листа, доказывает, что распределение поля есть векторная величина. 2) При двух угловых положениях поляризатора повернутого на 90° "интенсивность практически равна нулю. 3) Из опыта с пленочным поляризатором следует, что световые волны являются поперечными волнами. 4) Свет, исходящий из естественного источника света называется неполяризованным (естественным). 5) Любое оптическое устройство, посредством которого передается только линейно-поляризованный свет, называется поляризационным фильтром (поляризатором).

Grammar Revision

3. Read and translate the following sentences focusing on the forms and functions of the Infinitive:

1) Screens made of transparent substances are frequently used to diffuse the light from a source. 2) To prevent aberrations the mirror must be of large aperture. 3) To obtain the algebraic relations we must make certain conventions (договоренность) concerning the sign to be attributed to the quantities considered. 4) The first attempts to measure the velocity, of light were made in 1667. 5) To obtain a 100% monochromatic light is impossible. 6) Probably one of the first optical phenomena to be noted was that the shadow of an object illuminated by a source of small dimensions had the same shape as the object. 7) Yu. Denisyuk was the first to propose three-dimensional media to be used for recording holograms. 8) One of the earliest optical instruments ever to be made was the humble (скромный) pair of spectacles. 9) A pair of spectacles has served to extend our useful life by at least 20 years.

4. Read and translate the following sentences paying attention to complexes with the Infinitive:

1) Most optical media have the same properties and are considered to be isotropic. 2) The great progress in all branches of optics may be said to have resulted indirectly from the invention of the electric lamp. 3) While the experiment was entirely correct in principle, we know the velocity of light to be too great for the time interval to be measured in this way with any degree of placation. 4) A pocket microscope deve­loped in 1702 is known to have produced magnifications up to 40. 5) The laser beam is a highly collimated bundle of rays and as such has proved to be of great help in many applications in industry, medicine, etc. 6) The matrix has turned out to be of great advantage in many scientific considerations. 7) Light is believed to be an electro-magnetic radiation at very high frequencies (10 cps). 8) We know a light beam to consist of thousands and millions of rays in a wide frequency range and at various states of polarization. 9) The incident wave was assumed to be monochromatic. 10) We believe the degree of polarization to be a maximum, when the angle of incidence equals the polarization angle.

5. Answer the questions about Text 3A:

1) What instrument was used in the experiment described to obtain polarized light? Describe the experiment. 2) What does the ex­periment with a sheet polarizer prove? 3) What does the trans­mitted intensity depend on? 4) What does the Malus law state? 5) Is optical disturbance scalar or a vector quantity? 6) What light is considered to be linearly polarized? 7) What is a polarizing filter?

6. Write an abstract of Text 3A.

7. Use the diagram above to speak about polarization.

8. Read Text 3B (time limit 5 min.) and speak about the principle behind a polarizing microscope operation.

TEXT 3 В A POLARIZING MICROSCOPE

When ordinary light is directed from the mirror to the polarizer, it emerges from the polarizer as polarized light. It passes on through the optical system to the analyzer. Since the vibration direction of the analyzer is set at 90 degrees to that of the polarizer, none pf the light which reaches the analyzer is allowed to pass to the eye the extraordinary ray coming from the polarizer has become the ordinary ray of the analyzer and it is therefore reflected out of the field of the microscope. The field appears black unless an object which rotates the plane of polarization interferes with the natural path of the light. This peculiarity (особенность) of the polarizing micro­scope is what makes it so valuable for analysis of many materials.

700 п. зн.

1. Translate Text 3C in writing using a dictionary (time limit 60 min.):

TEXT 3C WIENER’S METHOD

То observe the interference between incident and reflected waves is not an easy matter, mainly because the distance between the planes of maximum and minimum intensity is less than one wavelength. The problem, however, can be solved with a technique devised by Wiener. A very thin film of photographic emulsion is placed at a small angle to the reflecting sur­face, if the incident light is in the appropriate state of polarization, the film developed will show a series of light and dark bands, the maximum darkening occurring along the lines where the plane of the film intersected the planes of maximum intensity.

This technique was a very important one historically be­cause it provided the first experimental determination of the plane of light waves. Most other polarization experiments, in fact, -while proving the existence of linearly polarized light, do not furnish information about the actual direction of the vector representing the optical disturbance. For example, the experiment described in Section 3 - I shows a sheet polarizer to transmit only light waves whose optical vector is parallel to a certain preferred direction. It does not enable us to mark this preferred direction. It does not enable us to mark this preferred direction on the sheet. We can now do so by per­forming Wiener's experiment with light that has gone through the sheet polarizer. We repeat the experiment a number of times, rotating the«sheet in its own plane between exposures of the photographic films, until the interference bands become shar­pest or until they disappear completely. In the first instance the transmission axis of the polarizer will be the di­rection parallel to the reflecting surface. In the second instance, it will lie along the intersection of the plane of the sheet with the plane of incidence.

1800 п. зн.

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