Read the following international words and check their pronounciation in a dictionary.

Carbon dioxide, electron, helium, hydrogen, molecule, neutron, proton, quantum mechanics, subatomic, universe

Match these words with their definitions.

1. subatomic A) part of an atom which has no charge

2. electron B) two or more atoms

3. neutron C) smaller than an atom

4. molecule D) part of an atom that has a negative charge

5. proton E) a theory developed by physicists to explain the atom

6. quantum mechanics F) part of an atom which has a positive charge

7. carbon G) pulled together

8. attracted H) a chemical element

9. helium I) a chemical element that is lighter than air

10. universe J) the whole cosmos

Comprehension

Choose the correct answer and complete the sentences.

1 Dalton believed the atom to be

A) an element. B) made of smaller particles.

C) the smallest possible particle. D) his own idea.

2 Dalton's theories were

A) generally accepted. B) not tested very carefully.

C) accepted at once. D) not correct.

3 The number of protons in an element

A) is the same as the number of electrons. B) is always six.

C) never changes. D) characterizes the element.

4 Electrons help

A) protons to form elements. B) atoms to be neutral.

C) molecules to become atoms. D) atoms to form molecules.

5 Hydrogen is

A) the simplest atom there is. B) present in all atoms.

B) C)the oldest atom. D) as common as helium.

Writing

Write a short essay on the steps of atom structure study (80-100 words).

Unit 4

Before you read

Answer the following questions.

1. Your future research work will be connected with optical devices namely lasers. What is LASER?

2. What types of lasers exist?

Give the translation of the following terms from the text below. Use the dictionary if necessary.

1. energized atoms 8. gas lasers

2. light amplification 9. visible red light

3. stimulated emission 10. semiconductor lasers

4. exited state 11. dye lasers

5. light released 12. diode lasers

6. solid state lasers 13. use low power

7. pumped 14 discharge

Read the text and find the answers to the questions of 4.1.

Laser Basics

Lasers play a pivotal role in our everyday lives. The fact is they show up in an amazing range of products and technologies. You will find them in everything from CD player to dental drills, from high-speed metal cutting machines to measuring systems. Tattoo removal, hair replacement, eye surgery – they all use lasers. But what is a laser? What makes a laser beam different from the beam of a flashlight? What are the main types of lasers?

Let’s start with the fundamentals of laser technology.

A laser is a device that controls the way that energized atoms release photons.”Laser”. is an acronym for light amplification by stimulated emission of radiation. In a laser, the lasing medium is “pumped” to get the atoms into an exited state. Typically, very intensive flashes of light or electrical discharges pump the lasing medium and create a large collection of exited-state atoms (atoms with higher-energy electrons). It is necessary to have a large collection of atoms in the exited state for the laser to work efficiently.

Laser light has the following properties:

*the light released is monochromatic. It contains one specific wavelength of light (one specific colour),

*the light released is coherent. It is “organized” – each photon moves in step with the others,

*the light is very directional. A laser light has a very tight beam and is very strong and concentrated. A flashlight, on the other hand, releases light in many directions and the light is very weak and diffuse. To make these three properties occur takes something called stimulated emission. This does not occur in your ordinary flashlight – in a flashlight, all of the atoms release their photons randomly. In stimulated emission, photon emission is organized. The other key to a laser is a pair of mirrors, one at each end of the lasing medium. In the process, they stimulate other electrons to make the downward energy jump and cause the emission of more photons of the same wavelength and phase.

There exist some different types of lasers. The laser medium can be a solid, gas, liquid or semiconductor. Lasers are commonly designed by the type of lasing material employed.

Solid-state lasers have. lasing material distributed in a solid matrix (such as the ruby).

Gas lasers (helium and helium-neon are the most common gas lasers) have a primary output of visible red light.

Excimer lasers (the name is derived from the terms excited and dimers) use reactive gases (chlorine) mixed with inert gases (argon and xenon).

Dye lasers use complex organic dyes in liquid solution as lasing media.

Semiconductor lasers or diode lasers. These electronic devices are very small and use low power.

Thus, a laser is created from light, and the resulting laser light has special properties that are unique and different from regular light. A laser can be of different types and strengths. A laser can be very tiny so as to be almost invisible, and can be very large so as to occupy an entire room. The laser is indeed a very useful and exciting invention, with many beneficial applications and uses.

Vocabulary

1. emit (v) испускать, излучать (свет)

2. emission (n) испускание (света), эмиссия

3. emitted (adj) излученный

4. release (v) испускать, выбрасывать

5. amplify(v) усиливать

6. amplification (n) усиление

7. stimulate (v) возбуждать, индуцировать

8. wavelength (n) длина волны

9. flashlight (n) мигающий свет, электрический фонарик

10. output (n) мощность

11. lasing medium среда, генерирующая в оптическом диапазоне

12. lasing material вещество, излучающее в оптическом диапазоне