Exercise 7. Describe the history of number usage.

 

Exercise 8. Explain why decimal fractions were introduced only in the 16^th century.

Exercise 9. Define the types of number systems. Analyze their differences and similarities.

Exercise 10. Discuss the text according to the points:

1. The history of number usage.

2. The main types of number systems.

3. Digits, digit sequences in the decimal and the binary systems.

 

                                             Notes:

1. figure = number = digit = sign

2. numerals –                                 числівники

3. scale –                                        шкала

4. finger –                                      палець

5. comparison –                             порівняння

6. rarely employed = seldom used

7. common / decimal fractions –    прості та десяткові дробі

8. notation = concept

9. power ( by a power) –               ступінь    

10. product –                                 добуток

11. to yield –                                 створювати

12. sequence -                               послідовність.

 

 

LESSON 4

RADIATION

Key terms : conduc|ion, convection, radiation, transfer, visible light, ultraviolet rays, infrared light, microwaves, radio waves, electromagnetic spectrum, vacuum, wavelength, radiator, absorber, emitter

1. Suppose you touch the surface of a hot water tank with your hand. Heat travels from the hot water through the metal to your hand by conduction. Conduction can be defined as the movement of heat as a result of collisions between molecules. Hold your hand above the water tank. Heat is now carried to your hand by convection currents of air. Convection is the trans­fer of heat by movement of the molecules from one place to another. Hold your hand off to the side of the tank. Most of the heat reaches your hand by a process called radiation.

2. Radiation is the transfer of energy by means of electromag­netic waves. Electromagnetic waves include gamma rays, X-rays, ultraviolet rays, visible light, infrared light, microwaves and radiowaves. Figure 3 shows the approximate wavelengths of the electromagnetic spectrum. Heat radiation is the infrared portion of this spectrum. Electromagnetic waves travel through a vacuum at a speed of light and can also travel through gases. This is how the energy from the Sun reaches us.

3.  The surface of any object Continually emits radiant energy over a range of wavelengths. The energy emitted by the object depends on the nature of the surface and on its temperature. At room temperature the emission is small, occurring chiefly in the form of long infrared waves. These wavelengths are invisible to the eye. The rate of emission by a hot incandescent filament at a temperature of 3000°C is much larger. Although most of the energy is still in the form of infrared waves, it now also contains much shorter wavelengths that the eye is able to detect.

 

4. The best radiators have black surfaces. For this reason, car radiators and heat exchangers, such as cooling coils on the back of refrigerators, are painted black. The best emitter of radiant energy is also the best absorber. That is why the cool absorbing surface of a solar collector, trapping radiant energy from the sun, is black. Radiant energy absorbed by any surface becomes thermal energy.

5. The poorest emitter and absorber of radiant energy is the best reflector. This explains why we wear white clothing in the summer. It also explains why the inside of thermos bottles are silvered and why the outside of kettles are light coloured.

6. Every object continually absorbs and emits radiant energy. The greater the temperature difference between a body and its surroundings the faster the transfer of energy. A body cooler than its surroundings absorbs more radiant energy than it emits and, as a result, heats up. Conversely, a body hotter than its surroundings emits more radiant energy than it absorbs, and so cools down. A cup of hot tea loses radiant energy much faster than a cup of warm tea.

 

Exercise 1. Find synonyms in the text to the following words:

1. reservoir (1)                                                    6. to move (1)

2. to happen (3)                                                   7. to radiate (3)

3. mainly (3)                                                       8. to discover ( the existence or presence) (3)

4. to make clear (5)                                             9. always (3, 6)

5. a share (2)                                                       10. environment (6)

 

Exercise 2. Classify the words into international and terms:

Thermos; microwaves; ultraviolet rays; molecule; metal; spectrum; radiator; refrigerator; solar; gamma rays; collector; heat exchangers; x-rays; energy; absorb; process; vacuum; wavelength; incandescent filament; temperature; emission.

 

Exercise 3. Say if the statements are true or false:

1. Conduction, convection, radiation are the examples of energy transfer.

2. Electromagnetic waves are invisible to the man’s eye.

3. Radiant energy can be emitted and absorbed by any object.

4. The best emitters are the best reflectors.

5. Long infrared waves are invisible and short infrared waves are visible.

 

Exercise 4. Complete the sentences choosing the right variant:

1. If you touch the hot object, heat travels from it to your hand by…

a). convection

b). conduction

c). radiation

 

2. Heat radiation is the… portion of spectrum.

a). ultraviolet

b). infrared

c). microwaves

 

3. The rate of emission depends on…

a). wavelength

b). temperature

c). surroundings

 

4. The worst emitter of radiant energy is the best…

a). absorber

b). collector

c). reflector

 

5. A body cools down if it emits more… than it absorbs.

a). thermal energy

b). heat energy

c). radiant energy.

 

Exercise 5. Answer the following questions:

1. What ways do electromagnetic waves include?

2. How does the energy of the Sun reach us?

3. What factors affect the radiant energy emitted by an object?

4. Why do we tend to wear dark-coloured clothes in winter and light-coloured clothes in summer?

5. Why are emitters and absorbers grouped together and opposed to reflectors?

 

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