Properties of Light

Exercise 9. Complete the following sentences with the words above.

Study the following words

Exercise 8. Complete the sentences using the words in brackets.

Pattern: If I had time to spare, (go to the cinema).

If I had time to spare, I’d go to the cinema.

1. If we knew hoe to operate the device, (to use it). 2. If we raise the temperature, (to heat a body). 3. If the problem were easy, (to solve it). 4. If they had been at home yesterday, (to visit them). 5. If a bar of iron were placed in a strong magnetic field, (to experience strong forces). 6. If electrons pushed their way through the metal, (to encounter continuous opposition). 7. If we used electron streams as a source of heat, (to pass a current through a thin wire). 8. If the wire were made from an alloy such as nichrome, (to offer a considerable resistance to the electrons). 9. If our intention were to use the electric current as a source of light, we (to use a metal such as tungsten). 10. If the iron came under magnetic forces, the particles (to orient themselves). 11. If iron of certain type were placed inside a coil through which electricity is passed, (to become a “permanent magnet”). 12. If the current were switched off, an electromagnet (to lose its magnetism). 13. If the temperature had not been raised, the body (not to have been heated). 14. If we hadn’t considered the principles of electric and magnetic dipoles, (to obtain a better understanding of the principles of electricity and magnetism). 15. If we had not used the definition, (to determine the value of the force). 16. If a bar specimen had been placed free to move in a magnetic field, (to line up parallel to the external field).

arrangement (n) – домовленість, розміщення, класифікація; arrangement by numbers

cast (v) – кидати, направляти; to cast an eye – кидати погляд

emanate (v) – випромінювати; бути результатом чогось

incandescent (adj) – розпечений, яскравий, той, що світиться

inverted (adj) – перевернутий, повернутий у зворотному напрямку

pinhole (n) – точений отвір (наприклад, діафрагми)

propagation (n) – відтворення, походження (сигналу)

radiate (v) – випромінювати

realm (n) – сфера, галузь

rectilinear (adj) ‑ прямолінійний

1. The shape looked like an … V. 2. At the end of the speech he seemed to be moving into the … of fantasy. 3. The setting sun … an orange glow over the mountains. 4. Be sure that the … is closed not to blacken the film. 5. … motion means motion in a straight line. 6. I don’t think that we have enough knowledge to set the … of that strange noise. 7. He … power and confidence. 8. Heat … from the stove. 9. They had an … that the children would spend two weeks with each parent. 10. She was … with rage.

TEXT 1

Light and its various phenomena present some of the most interesting studies in the whole realm of physics. They are interesting because the results of many experiments are revealed through the sense of vision as colour phenomena. Equally important and every bit as interesting is the historical development and the discovery of the various principles, concepts, and properties of light which give rise to this phenomena.

All of the various known properties of light are conveniently described in terms of the experiments by which they were discovered and the many and varied experiments by which they are now continually demonstrated. Numerous as they are, these experiments may by grouped together and classified under one of the three following heads: 1) geometrical optics, 2) physical optics, and 3) quantum optics. Each of these may be subdivided as follows: geometrical optics: rectilinear propagation, finite velocity, reflection, refraction; physical optics: diffraction, interference, polarization, double refraction; quantum optics: photoelectric effect, Compton effect, atomic excitation, pair production.

The rectilinear propagation of light is another way of saying that “light travels in straight lines”. The fact that objects may be made to cast fairly sharp shadows is an experimental demonstration of this principle. Another illustration is the image formation of an object which is produced by light passing through a small opening. An object can be ordinary incandescent light bulb. In order to see how an image is formed, consider the rays of light emanating from a single point a near the top of the bulb. Of the many rays of light radiating in all directions, the ray that travels in the direction of the hole passes through the point a' near the bottom of the image screen. Similarly, a ray leaving b near the bottom of the bulb and passing through the hole will arrive at b' near the top of the image screen. Thus, it may be seen that an inverted image is formed.

If the image screen is moved closer to the pinhole screen, the image will be proportionately smaller, whereas if it were moved farther away the image would be proportionately larger. The same thing happens when either the object or the pinhole is moved. Excellent photographs can be made with this arrangement by making a pinhole in one end of a small box a placing a photographic film or plate at the other. Such an arrangement is called a pinhole camera. For good, sharp photographs the hole must be very small, because its size determines the amount of blurring produced.

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