"To be" and its functions. "To have" and its functions

V. Translate the sentences and explain the use of modal verbs:

1. 
   Electric current can produce certain chemical actions.
   
2. 
   The transformer can reduce the AC voltage to values which are used for various instruments.
   
3. 
   The digital computers can perform the operations of arithmetic: addition, subtraction, multiplication, and division.
   
4. 
   These poles must have existed in the original magnet.
   
5. 
   Where greater accuracy is required, you must employ digital computers.
   
6. 
   These troubles may result from constant use or from some other reason.
   
7. 
   It is necessary that a modern engineer must know not only some of the fundamental tube types, but also a few typical applications.
   
8. 
   While some electrons may be free to move within the conductor, there exists an effect on the surface of conductors that is similar to surface tension
   
9. 
   Electron emission can take place more easily in some materials than in others.
   
10. 
    We may effectively control the anode current by means of the grid.
    
11. 
    Semiconductor devices can perform the elementary functions of oscillation, application, modulation and demodulation and rectification.
    
12. 
    The bulb connected across this circuit cannot light since it has an open in the main line.
    
13. 
    An open in one element opens only one branch while all the other branches can operate.
    

VI. Translate the sentences. Pay attention to the use of modal verbs and their equivalents.

1. 
   One should take into consideration that the positive terminal of the meter is connected to the positive terminal of the source.
   
2. 
   The first law explains what is to be understood by force.
   
3. 
   To compare electric currents we should have certain units by means of which they are to be measured.
   

4. The term "computer" refers not only to complete equipment which is able to perform much operation, but to the simple computing elements used in electronic equipment.
5. One should mention that electrodes are in a state of continual vibratory motion.
6. Amplifiers are often used as relays which are to open and close circuits in power systems when needed.
7. The electron is able to recombine with the impurity ion.
8. The direct recombination of electron and hole is to be avoided if devices are to work properly.
9. Atoms of the impurity material .have to be small enough to fit into the crystal lattice where they replace a few of the semiconductor atoms.
10. Тhe donor is able to give up electrons under relatively small thermal excitation.
11. The other part of the thermoelectric voltage had to do with contact potential differences between the metal and semiconductor.
12. One should not forget that the heat produced in the electric circuit is of great practical importance for heating, lighting and other purposes.
13. One might call production of heat "the light effect" as it gives off light as well as heat.

14. 
    When an electric current is passed through a wire, it will be allowed to heat it and even cause it to become red-hot.
    

15. Such heat is desirable at times, but at other times we must remove or decrease it.