Grammar: Tense Forms in Active (Review)

Контрольна  робота №5

для студентів заочного факультету

(спеціальність: електромеханіка)

1 варіант

 

Grammar: Tense Forms in Active (Review)

 

I. Read the text and translate it in writing.

 

Electric Circuits

The concepts of electric charge and potential are also essential in the study of electric currents. When an extended conductor has different potentials at its ends, the free electrons of the conductor itself are caused to drift from one end to the other. In order for this flow to continue it is necessary that the potential difference be maintained by some electrical source such as an electrostatic generator, or, much more frequently, a battery or a direct-current generator. The wire and the electrical source together form an electric circuit, the electrons drifting around it as long as the conducting path is maintained. In effect such a flow of electrons constitutes an electric current.

Batteries and direct-current generators are sources of potential difference which urge the electrons around a circuit continually in one direction, producing a unidirectional current. For this reason such a source is said to have a fixed polarity, one terminal being called positive and the other negative. If it is desired to reverse the flow, then the terminals of the circuit must be reversed with respect to the source.

From the early days of electrical science, current has been regarded as a flow of electricity from the positive terminal to the negative terminal in the external circuit connected to a source. Now we know a current through a conductor to be actually a movement of electrons, and since these have negative charges, they travel around the external circuit from the negative terminal to the positive terminal. The electron flow is, therefore, opposite to the conventional direction of current, making it necessary, in order to avoid confusion, to distinguish ore from the other by name.

 

II. Answer the following questions:

1. What are essential in the study of electric current?

2. What do form an electric circuit?

3. What does constitute an electric current?

4. When must the terminals be reversed with respect to the source?

5. How is a current known in our days?

 

III. Match the words:

 1. charge        1. невід’ємний, необхідний

 2. essential 2. провідник

 3. conductor 3. заряд

4. circuit 4. струм

5. current 5. джерело

6. source 6. коло

7. direction 7. спонукати, підганяти

8. urge 8. зовнішній

9. external 9. напрямок

10. confusion        10. збентеження

 

 

 

 

 

 

 

 

IV. Choose the right variant from those given in brackets:

1. Atoms ... electrons which are negatively charged, protons which are positively charged and neutrons which have no charge, (contains, contain, contained)
2. Common sources of electricity... batteries and power plants, (is, are, to be)
3. Electricity... through transmission lines to houses, factories (to flow, flows, flowed)
4. Such free electrons... always present in metals, (is, are, to be)
5. People always ... their surroundings (polluted, to pollute, were polluting)
6. A generator is a machine that... mechanical energy into electrical energy, (converts, were converting, to convert)
7. These coils ... the magnetic lines of force, (to cut, cut, cuts)
8. Pollution ... streams, lakes unpleasant to swim in or to have a rest, (to make, makes, were making)
9. A typical commutator ... of commutator bars, (consists, to consist, consist)
10. Because series generators ... poor voltage regulation, only a few are in use (has, have, to have)

 

V. Finish the following sentences according to the text:

1. ... are also essential in the study of electric currents.
2. In effect such a flow of electrons ....

• ... then the terminals of the circuit must be reversed with respect to the source.

4. When an extended conductor has different potentials at its ends ...

5. The electron flow is ...               6. The wire and the electrical source together ...

 

VI. Give summary of the following text and be ready to speak on this topic.

There are a variety of amplifier designs that couple a class AB output stage with  other more efficient techniques to achieve a higher efficiency with low distortion. These designs are common in large audio amplifiers, for instance, since the heatsinks and power transformers would be prohibitively large (and costly) without the increase in efficiency. The terms "class G" and "class H" are used interchangeably to refer to different designs, varying in definition from one manufacturer or paper to another.

Class G amplifiers are a more efficient version of class AB amplifiers, which use "rail switching" to decrease power consumption and increase efficiency. The amplifier has several power rails at different voltages, and switches between rails as the signal output approaches each. Thus the amp increases efficiency by reducing the wasted power at the output transistors.