Generators

One of the most important scientific discoveries was made by Michael Faraday in 1831. Faraday found that when a magnet is moved near a coil of wire, an electric current is produced in a coil. He also discovered that when a current is switched on and off in one coil a changing magnetic field is created around the coil and that this changing field will create another current in a second nearby (находящийся рядом) coil. The current in the second coil is much greater if both coils are wound on the same iron core. This process of producing electricity from magnetism is called electromagnetic induction. The electric generators, or dynamos, that supply us with the vast amounts of electric power needed today have all been developed from Faraday's discovery. They operate on the same principle as the one invented by the great English scientist. A dynamo consists of many coils of wire wound on an Iron core (armature) which is rotated on a shaft between .the poles of an electromagnet. The current is generated in the coils when the armature is driven around. In a simple dynamo the current changes direction twice for each revolution of the coil. First it builds up to a positive peak. Then it returns to zero before building up to a positive peak again. This is called alternating current (a.c.) A graph showing how the current varies with time has the shape of a wave. To obtain direct current (d.c.) from a rotating generator requires a commutator with split rings (кольца с прорезью). Thus, 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. There are two types of dynamos, namely, the generator and he alternator. The former supplies d.c. which is similar 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. 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.

Engines

Do you know what the first engine was like? It was called the "water wheel". This was an ordinary wheel with blades fixed to it, and the current of a river turned it. These first engines were used for irrigating fields.

Then a wind-powered engine was invented. This was a wheel, but a very small one. Long wide wooden blades were attached to it. The new engine was driven by the wind. Some of these one can still see in the country. Both of these, the water- and wind-operated engines are very economical. They do not need fuel in order to function. But they are dependent on the weather.

Many years passed and people invented a new engine, one operated by steam. In a steam engine, there is a furnace and a boiler. The furnace is filled with wood or coal and then lit. The fire heats the water in the boiler and when it boils, it turns into steam which does some useful work. The more coal is put in the furnace, the stronger the fire is burning. The more steam there is the faster a train or a boat is moving. The steam engine drove all sorts of machines, for example, steam ships and steam locomotives. Indeed, the very first aeroplane built by. A.F. Mozhaisky also had a steam engine. However, the steam engine had its disadvantages. It was too large and heavy, and needed too much fuel.

The imperfections of the steam engine led to the design of a new type. It was called the internal combustion engine, because its fuel ignites and burns inside the engine itself and not in a furnace. It is smaller and lighter than a steam engine be­cause it does not have a boiler. It is also more powerful, as it uses better-quality fuel: petrol or kerosene.

The internal combustion engine is now used in cars, diesel, locomotives and motor ships. But to enable aeroplanes to fly faster than the speed of sound another, more powerful engine was needed! Eventually, one was invented and it was given the name "jet engine"-The gases in it reach the temperature of over a thousand de­grees. It is made of a very resistant metal so that it will not melt.