The Generators

Exercise 4. Match the sides.

Exercise 3. Answer the questions.

Exercise 2. To translate the following text.

Magnetism

Exercise 3. (Put 10 questions to the text.)

Exercise 4. ( Translate paying attention to the word "due to".)

1) Due to friction the part of energy developed by mechanical devices is lost in the form of heat.

2) Due to the existence of potential difference the current flows in the circuit.

3) In this case the motion of electrons is due to the electric field.

The study of electricity can be divided into three branches: magnetism, electrostatics and electrodynamics. Magnetism is the property of the molecules of iron and some other substances to store energy in a field of force. Electrostatics is the study of electricity at rest. Rubbing glass with a silk produces static electricity. Electrodynamics is the study of electricity in motion, or dynamic electricity. The electric current which flows through wires is a good example of the dynamic electricity.

A difference of electrical pressure is necessary to maintain a flow of electricity in a conductor. Different substances differ in electrical conductivity. Atoms of many substances give up electrons with ease. Electrical energy has intensivity and quantity.

Questions:

1) What branches of electricity do you know?

2) What is magnetism?

3) Electrostatics is the study of electricity at rest, isn't it?

4) What does the term "electrodynamics" mean?

5) Do different substances differ in electrical conductivity?

1.To story energy in the field of force	1.Мати інтенсивність і кількість
2.To produce static electricity	2.Запасати енергію в силовому полі
3.A difference of electric pressure	3.Відрізняються за електропровідністю
4.To differ in electrical conductivity	4.Різниця електричної напруги
5.To have intensivety and quantity	5.Виробляти статичну електрику

Exercise 5. Retell the Text “Magnetism”.

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Тема 16-17

Генераторы.

"Generators"

Exercise 1. (Read and translate the text)

You have learned, that the magnetic lines of force radiated about an electromagnet can be picked up by a coil of wire; this is known to be the principle of the induction coil. A coil of wire revolving or turning in a magnetic field also picks up the lines of force. The ends of the coil are connected to the wires, which are not turning by means of wheels upon which there are two insulated contact surfaces. These wheels are known to be called commutators. Two brushes are installed to rub or contact the two contact surfaces of the commutator. Thus, each time the coil turns and cuts the lines of force, a pulse of current is collected by the coil, to flow out of one of the commutator contacts, to the brush contacts, and then to return through the other brush and commutator contact.

There are generators, which produce direct current and those, which produce alternating current. The flow of current from the d.c. generator is always "direct". The current always flows out of one pole and back into the second pole. The flow from an a.c. generator "alternates", the current first flowing out of one pole and back to the second, then out of the second and back to the first, etc.

Exercise 2. (Translate the sentences paying attention to the ing-forms.)

1. The new instrument being developed at this plant will be test­ed in two weeks.

2. Two bodies having potentials of 100 volts and 50 volts, a po­tential difference of 50 volts exists between them.

3. Leaving the room we turn the light off.

4. An insulator is a substance, which contains no free electrons, glass, paper, rubber being the most common nonconductors.

5. Having defined two units of power, the horsepower and the kilowatt, we may use them to define two new units of work, the horsepower-hour and the kilowatt-hour.

6. The positive pole having been brought near the negative pole, the latter attracts the positive pole.

7. When rubbing a glass rod with a piece of silk, you develop a large difference of potential.

Exercise 3. (Retell the Text.)

"The Care of the Generators"

Exercise 1. (Read the text)

The care of GENERATORS

The dynamo invented by Faraday in 1831 is certainly a primitive apparatus compared with the powerful, highly efficient generators and alternators that are in use today. Nevertheless, these machines operate on the same principle as the one invented by the great English scientist. When asked what use his new invention had, Faraday asked in his iurn: "What is the use of a new-born child'" As a matter of fact, "the new-born child" soon became an irreplaceable device we cannot do without.

Although used to operate certain devices requiring small currents for their operation, batteries and cells are unlikely to supply light, heat and power on a large scale., Indeed, we need electricity to light up millions of lamps, to run" trains, to lift things, and to drive the machines. Batter­ies could not supply electricity enough to do all this work.

That dynamo-electric machines are used for this pur­pose is a well-known fact. These are the machines by means of which mechanical energy is turned directly into electrical energy with a loss of only a few per cent. It is calculated that they produce more than 99.99 per cent of all the world's electric power.

There are two types of dynamos, namely, the generator and the alternator. The former supplies d.c. which is simi lar to the current from a battery and the latter, as its name implies provides a.c.

To generate electricity both of them must be continuous­ly provided with energy from some outside source of me­chanical energy such as steam engines, steam turbines or water turbines, for example Both generators and alternators consist of the following principal parts: an armature and an electromagnet. The electromagnet of a d.c. generator is usually called a stator for it is in a static condition while the armature (the rotor) is rotating. Fig. 7 shows the principles the construction of an elementary d.c. generator is based upon.

Exercise 2. (Translate the text)

Exercise 3. (Put 10 questions to the text)

Exercise 4. (Retell the main idea from the text)

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