2. Fill in the gaps using the following verbs: break, free, move, come, occur, appear.

Fig. 1. A hole has appeared at point A	- Figure 1 shows a part of a silicon crystal in which the breaking of covalent bonds is taking place. Was this caused by heating? Yes, by heating. In Figure 1 it is shown that one covalent bond … and an electron … itself. A hole … at point A.
- Will you be able to explain what is taking place in the next figure (Fig. 2)? - Yes, of course. A hole … at point B and now two electrons can move through the crystal.	F ig.2. A hole has appeared at point B.
Fig. 3. Hole A has disappeared and hole C has appeared	- Look at Fig. 3. The second electron … close enough to the first hole and is attracted by its electric field. Recombination … . Now there is no hole already at point A. But still there is a hole at point B. It seems that the hple… from position A to position B. - Looking at this figure, it becomes clear that one more hole … at point C.
As shown in Fig.4 the third free electron … through the crystal lattice. Again recombination … and a hole … . The effect is as though a hole … from point A to point C.	Fig. 4. Hole B has disappeared

3. Make up sentences using Present Perfect. Use the prompts in brackets. Mind the position of just/already/yet.

1. How have you decreased the capacitance of your system?

I have just connected equal capacitors in series.

(I/just/connect/equal/capacitors/in series)

2. Can we observe any changes in the movement of electrons and holes?

Of course, we can, but …

(only/when/process/of recombination/already/occur)

3. Could you stop the movement of holes quite fast?

No, …

(I/just/heat/a peace of silicon)

4. Have you already changed a random character of movement of holes in a piece of germanium?

Unfortunately …

(I/not/apply/any/voltage/yet)

5. Do you consider me an expert in a problem of the movement of holes?

No, …

(I/already/consider/a lot of/important/things/but not all)

6. Could you increase the amplification factor of our circuit?

Yes, …

(I/already/replace/a triode/for a tetrode)

4. Open the brackets and complete the dialogues with just, already, yet. Use Passive Voice where nessesary.

1. A: How do we call the phenomenon of attracting an electron by electric field?

B: Don’t you know that the scientists … (call) this process recombination?

2. A: I learned about the intrinsic conduction yesterday .

B: Yes, but you … (not/consider) in what types of materials it takes place.

3. A: Do we have a method to divide the flow of electrons and holes?

B: I … (do) this by means of applying voltage.

4. A: There is no sense to look for different ways of controlling the increase of temperature in a triode. How do you think, why?

B: I think, because a Centigrade scale … (invent).