Applications of the electromagnet

Electromagnets always find an application when it is de­sirable to convert electrical power into mechanical power.

Telegraph systems and telephones, relays, motors and generators, radio sets and television sets, electrical measuring instruments as well as thousands of other valuable and neces­sary devices are known to contain electromagnets. They may be used, as well, to protect electrical circuits against over­loads and underloads.

One of the first applications of the electromagnet was in telegraphy. Shilling, corresponding member of the Peters­burg Academy of Sciences was the first to construct the electromagnetic telegraph. He demonstrated his invention as far back as 1832.

As mentioned above, the telephone also uses electromag­nets, uses many of them, in fact. As soon as man learned to send word over the long wires of the telegraph circuit, the next problem to be solved was the telephone. Was it not pos­sible to send the spoken word over similar wires? As a matter of fact, the first practical telephone was invented by the Amer­ican scientist Bell in 1876 and was further improved by Edison.

FUSES

A fuse is a safety device that protects electric circuits from overloads. It must be put in every circuit where there is danger of overloading the line. All the current used must pass through the fuse, the latter being the weakest link in the circuit.

Such a safeguard is quite necessary. For no matter how careful you are, there is always the possible danger of a short-circuit, or an overload on some appliance. This means that an unusually large electric current will flow. If a short

circuit or overload caused more current to flow than the car­rying capacity of the wire, the wire would become hot. It might set fire to the insulation were it not for the fuse.

What actually takes place is simple enough. The fuse wire has a lower carrying capacity than the circuit it protects. Its melting temperature is low. Thus, the fuse will get hot and melt if the current becomes too great. In other words, if the current flow is greater than the carrying capacity of the fuse, the latter melts resulting in an open circuit.

As said before, all conductors have some resistance. In any conductor, heat is caused by the current's flow overcoming this resistance. The greater the current, the hotter the wire becomes. That is why the fuse melts when there is an overload The heat produced automatically stops the current flow.

If you examine several fuses, you will see that they are rated in amperes. The fuse will melt in case the current becomes greater than the rating. Therefore a I5-ampere fuse will melt and break the circuit if the current exceeds 15 amperes

Electric circuits can also be protected with circuit breakers. A circuit breaker is a switch with a heating element о a magnetic coil in it. The heating element becomes hot i the current is too great. When the element is hot, the switch opens the circuit automatically. In the other type of breaker the circuit is broken by the pull of the magnetic coil.

Circuit breakers are made in different sizes for different circuits.

THE STRUCTURE OF THE ATOM

The atom is the basic particle of all matter. All solids gases, liquids are composed of atoms.

For a time the atom was considered to be indivisible, but then it has been found that the atom in its turn can be divided into many different components.

In dividing the atom the man releases forces of great magnitude. These are forces that bind the central core of the atom This central core—the nucleus—is extremely small in diameter

The nucleus of the atom is of a highly complex structure It is the three main components of the atom that we shall deal with below. These are called protons, neutrons and electron;

The proton carries a positive charge of electricity, the number of protons in the nucleus determining the element that the atom forms.

For example, if the nucleus has a single proton, then it will form the gas hydrogen, if 92 protons are present, the element will be uranium and so on. In short, if the number of protons in the nucleus is known, the element can be found out at once.

As mentioned above, the proton carries a charge of positive electricity. We know the bodies charged with the same kind of electricity to repel one another. When two protons are brought close together they repel one another with a great force.

The second of these basic components of the nucleus is the neutron. The neutron does not carry a definite electric charge. The sub-particles that form the neutron do carry charges but the charge of one balances that of another leaving the neutron neutral. It is from this state that it gets its name.

The third component of the atom is the electron. The electrons revolve around the nucleus. Each electron carries a negative charge of electricity that is equal to the positive charge of a proton in the nucleus.

As the charge of the electron is negative and that of the proton positive, it might be thought that the proton would attract the lighter electron and draw it into the nucleus. This would happen if the electron were not revolving around the nucleus.

The speed of the electron establishes sufficient centrifugal force so that it counteracts the neutral attraction. Thus the higher the speed of the revolving electron, i. e. the greater its power, the farther from the nucleus it will revolve.

PHOTOELECTRIC EMISSION

Electrical power is transformed into light power in the electric lamp. Can light power be changed back to electrical power? The first discovery came in 1887 when Heinrich Hertz, the prominent German scientist who is known as the "father of radio," made a great discovery. He discovered that, for a given electromotive force, an electric spark will jump across a larger gap if this gap is illuminated by ultraviolet light than if the gap is left in the dark.

The second discovery came about a year later when it was found that ultraviolet light falling upon a negatively-charged metal plate caused it to lose its charge. If the plate was charged positively, there was no apparent change. The final discovery came about ten years later when Joseph J. Tomson, the famous English scientist, discovered that ultraviolet light falling upon a metallic surface caused it to emit electron' The emission of electrons under the impact of light power is called photoelectric emission. The more intense the light the more electrons are emitted by the exposed to light metal Although most metals will emit electrons when their surface are exposed to ultraviolet light, some metals, such as sodium potassium, and certain others, will emit electrons when exposed to ordinary visible light rays and infrared rays a well.

MAN AND HIS MACHINES

In all his activities, man now makes use of a lot of machines. Although most of these are of quite recent origin, afew simple ones have come down from very ancient times

The arrow, for example, was well known to man since prehistoric times, since it was only by hunting that he could get his food. The wheel, one of the greatest inventions eve; made by man, is also of prehistoric origin. A two-wheeled carriage is represented widely in his art and literature. The lever is probably of equally ancient origin. It is mentioned by the Greek philosopher Aristotle as a means of lifting a great weight by using a very small force.

After Aristotle there was little change in the number and kind of machines in use for nearly twenty centuries. Since then one new device after another has come to displace others that were less efficient only to be displaced in turn by other devices still faster or better. Let us have a look at a few of these changes.

In going from his home in Mount Vernon to New York to be inaugurated as the first President of America, Washington travelled in a horse-drawn carriage. The roads were extremely difficult to travel. The travel of a little over two hundred miles required seven hard days. That is a speed of about 35 miles a day. Men could travel by land in only two other ways—on foot and on horseback. Within half a century of that time a few short railways had been built in three different parts of the country. At first the trains were drawn by horses; in 1831 the first steam locomotive to be used in America was put into use. The "iron horse" soon proved its efficiency. New lines were designed and old ones extended. A speed of 35 miles a day had given way to regular schedules exceeding 35 miles an hour.

In the first decade of the present century it was thought that the limit of desirable speed had been reached. But the substitution of diesel and electric engines for steam engines and numerous other improvements have shown that much higher speeds may be easily achieved. Modern transportation uses electricity in many ways. Without it transportation, as is known today, could not exist.

On the other hand, modern life would be unthinkable without modern means of transport. To reach any part of the world is a matter of hours or days, while a century or two ago it took weeks, sometimes even months or years. Nobody could have imagined then the speed of our airplanes.

Now let us have a look at a few facts and figures concerning Moscow transport. According to historical documents one-horse cabs appeared in Moscow as early as 1586. Public trans­port was established only in the forties of the last century. The first lines for horse-drawn trams were built in 1872 and those for mechanized trams in 1903. Four years later there were already 800 trams in operation. The first eight buses appeared in the city 40 years ago, while today there are more than three thousand in operation. By the way, a Muscovite makes about 800 trips in buses, trolley-buses, the metro, and trams an­nually.