Check your understanding

Exercise 1. Answer the questions.

1. What do optical instruments use to modify light rays?

1. What kinds of images can be formed by mirrors and lenses?

2. What has influence upon the amount of bending?

3. What is an advantage of a lens over a mirror?

4. What is similar in microscopes, projectors and enlargers?

5. What telescopes are used most often in everyday life?

6. Why can reflecting telescopes be more powerful than refracting ones?

Exercise 2. Topics for discussion.

1. What do you know about optical prisms?

2. What can you tell about the use of telescopes?

Increase your vocabulary

Exercise 1. Read the collocations and translate them.

Intellectual horizons, transparent solids of glass, a predictable size and location, refractive index, curved glass lenses, in semi-permanent form, far-off objects, a convex objective lens, incident light rays.

Exercise 2. Match the synonyms.

Verbs

1	2
broaden	watch
bend	alter
devise	widen
modify	achieve
observe	curve
reach	reflect
pass	invent
	go
	enlarge
	enter
	leave
	travel

Nouns

1	2
aid	observer
device	beam
glasses	help
enlargement	fall
ray	eyepiece
viewer	spectacles
incidence	increase
	mechanism
	pupil
	goggles
	side
	speed

Exercise 3. State the part of speech of the following words and determine their meaning without using a dictionary.

1. approximate, to approximate, approximation, approximative, approximately;

2. most deficient, deficiency;

3. to emit, emitter, emission, emissive, emissivity;

4. the use, to use, user, using, usage, useless, useful, usefulness.

Exercise 4.

a) Make up singular-plural pairs.

Phenomenon, spectra, index, spectrum, radius, indices, phenomena, radii.

Language activity

Exercise 1. Summarize your knowledge of the functions of the verb “to be”. Translate the following.

1. The microscope has been improved and refined continuously throughout its history, that is practically since the 17^th century.

2. The main characteristics to be refined have always been the resolution and the elimination of aberrations.

3. The projection lens is to be especially corrected for curvature of field and distortion.

4. The purpose of the condenser is to concentrate the light coming from the mirror to a point approximately 1.25mm above the surface of its top lens.

5. The magnifying power of microscopes is being increased from year to year.

Exercise 2. State different meanings of “that (those)”.

1. тот, этот

2. что

3. который

4. заменитель существительного (that of)

5. то есть [that is = i.e. (id est - лат.)]

6. именно, только лишь (it is …that – усилительный оборот)

7. то, что

1. It is also worth pointing out that ruby lasers were extensively used in the past for military rangefinders.

2. Gas lasers are usually excited by electrical means, i.e., pumping is achieved by passing a sufficiently large current through the gas.

3. One of the most characteristic features of the He-Ne laser is that the output power does not increase monotonically with discharged current but reaches a maximum and thereafter decreases.

4. Since these pure rotational lasers are relatively less important than the other categories, we shall not discuss them further in the sections that follow.

5. That metals are good conductors of electricity is known to everybody.

6. It was the nature of p-n junction that happened to be one of the most difficult things for scientists.

7. At that time the engineers were testing a new semiconductor for the application in industry.

8. Semiconductor is a material having an electrical conductivity intermediate between that of metals and insulators.

9. Output energy and peak power in Q-switched operation are comparable to those obtainable with a Nd:YAG rod of comparable dimensions.

10. This was the laser scheme that was proposed in the original paper of Schawlow and Townes.

Exercise 3. Summarize your knowledge of Present Simple or Present Continuous. Put the verbs in brackets into the correct tense.

1. A lens (to be) a piece of glass, plastic or other transparent material curved on one or both sides.

2. Lenses (to refract) the light rays from an object forming an image.

3. I (to use, never) my mobile phone if I (to drive).

4. The walls of the house (to absorb) heat day after day.

5. The news bulletin (to begin) at 6 p.m.

6. In spring the days (to grow) longer and the nights (to become) warmer.

7. Jack often (to go) to the theatre. On Saturday he (to go) to see a new play.

8. Electromagnetic waves (to travel) in all directions through the Universe.

9. Some people still think the sun (to go) round the earth.