14. Read the text again and complete the sentences.

1. The rate of recombination of holes and electrons is always equal to … .

2. … causes a continual loss of holes and free electrons.

3. The material having equal concentrations of mobile electrons and holes is called … .

4. If the temperature of a silicon crystal is above absolute zero, … .

5. … is equivalent to a positive charge called ‘a hole’.

6. The total number of free electrons and holes is … .

7. … is able to attract electrons and can be filled by a passing electron.

8. The absence of an electron consists of … .

9. When an electron leaves the covalent bond it leaves … .

15. Match the terms in Table a with their definitions in Table b.

Table A	Table B
rate magnitude hole loss mobility	the speed at which something happens over a period of time. the great size or importance of something an empty space in something solid. the fact of no longer having something, or of having less of it than you used to have, or the process by which this happens the ability to move easily

Speaking

16. Summarize the text “Electrons and holes” in 150 words.

17. In pairs ask and answer text-based questions.

For example:

• What will occur if the temperature of the crystal rises above absolute zero?

• Can you explain what takes place in an atom when one electron frees itself from a covalent bond?

• Is the hole able to attract electrons?

• What can you say about the process of recombination?

• Can you say anything about the rate of recombination?

• And the total number of free electrons and holes is constant, isn’t it?

18. Divide into 2 groups. Group 1 translates Extract a and group 2 – Extract b of the text “Supernovae” with a dictionary in writing.

Extract A

A supernova (the plural is supernovae) is the explosion of a star. They are extremely important for understanding our Galaxy. They heat up the interstellar medium, distribute heavy elements throughout the Galaxy, and accelerate cosmic rays. But what causes a star to explode? And is there more than one type of supernova? Indeed, there seems to be two distinct types of supernovae – those which occur for a single massive star and those which occur because of mass transfer onto a white dwarf in a binary system. As you will see, however, it is only what gets the process started toward the explosion which differs between the two types.

Stars which are 8 times or more massive than our Sun end their lives in a most spectacular way; they go supernova. A supernova explosion occurs when there is no longer enough fuel for the fusion process in the core of the star to create an outward pressure which combats the inward gravitational pull of the star's great mass. First, the star swells into a red supergiant...at least on the outside. On the inside, the core yields to gravity and begins shrinking. As it shrinks, it grows hotter and denser. A new series of nuclear reactions begin to occur, temporarily halting the collapse of the core. But alas, it is only temporary.

Extract B

When the core contains essentially just iron, it has nothing left to fuse. Fusion in the core ceases. In less than a second, the star begins the final phase of gravitational collapse. The core temperature rises to over 100 billion degrees as the iron atoms are crushed together. The repulsive force between the nuclei is overcome by the force of gravity. So the core compresses but then recoils. The energy of the recoil is transferred to the envelope of the star, which then explodes and produces a shock wave. The shock then propels that matter out into space. The material that is exploded away from the star is now known as a supernova remnant. Another type of supernova involves the sudden explosion of a white dwarf star in a binary star system. A white dwarf is the endpoint for stars of up to about 8 times that of the Sun. The remaining white dwarf has a mass less than 1.4 times the mass of the Sun, and is about the size of the Earth. In a binary star system, the companion star of the white dwarf is often a red giant. The stars may be close enough to each other and the red giant large enough, that material may flow from the red giant onto the white dwarf. This results in a thermonuclear detonation of the entire star.

19. In Russian write a content-based summary of the text you have translated.

20. Translate into English the summary made in ex.19 of the text you haven’t read.

21. Make a reverse written translation (from Russian into English) of the extract you have translated.

22. Serve as simultaneous interpreter. Make an oral reverse interpretation of the text.

23.  Prepare a paragraph discussing the following question: ‘Will a Nearby Supernova Endanger Life on Earth?’ 

24. Find more information about Supernova and tell your group mates.