IX. Oral Practice.

Exercise 16. Prove that lightning performs useful services for mankind.

Exercise 17. Speak about the usefulness of lightning.

X. Reading.

Exercise 18. Read the text C for 8 minutes without a dictionary.

Text C.

Ball Lightning.

It is quite possible that there are several different physical forms of ball lightning and each form has its own characteristic set of properties. These phenomena are rare and this rarity leads to the wide variety of descriptions of ball lightning.

Lightning balls appear near the end of severe electrical storms. This happens after the air has been highly ionized and is filled with electromagnetic disturbances generated by the conventional lightning.

The diameters of observed lightning balls range from a few inches to rare instances of many feet. The average diameter of a ball is about 10 inches. The balls usually move by rolling or sliding along conductors such as telephone wires, fences, and other metallic objects.

The lifetime of a ball of lightning may range from a few seconds to minutes. The calculated surface temperature of a lightning ball can be 5,000°C.

The famous physicist Pyotr Kapitsa gave a reasonable explanation for a ball lightning. It appears at sufficient ionization of the air and the presence of vapours necessary for ionization of the rising current of air. The ionized clouds of plasma are composed of the atomic nuclei of gas stripped of their electrons. These nuclei possess their own periods of electromagnetic oscillations and are able to absorb the incoming external electromagnetic energy of the same period. This is known as the resonance effect.

Details of Kapitsa’s hypothesis include the reasoning that during the luminescence period, some energy is supplied continuously into the ball lightning and the energy source is outside the ball. This reasoning is based on the conservation of energy principle on the realization that the ball lightning is suspended in the air with no visible link with the energy source. Thus the only source of energy is the absorption of intense outside radio waves.

Notes:

disturbance – хвилювання;

conventional – звичайний;

to roll – котитися;

to slide – ковзатися, пливти;

vapour – випаровування, пара;

reasoning – міркування;

rising current of air – потік повітря, що піднімається;

to be composed of - складатися з ;

oscillations - коливання;

to strip – здирати;

to suspend – вішати.

Exercise 19. Skim the text once again. Now answer these questions in your native language.

1. Is there one or several forms of ball lightning?

2. When do lightning balls appear?

3. What is the average diameter of a ball lightning?

4. How do they usually move?

5. What is the lifetime of a ball of lightning?

6. What is the surface temperature of lightning ball?

7. Who gave a reasonable explanation for a ball lightning?

8. What happens during the luminescence period of the ball lightning?

9. What principle is his reasoning based on?

10. What is the source of energy for the ball lightning?

Exercise 20. Render the text in your native language.

Unit 5