Substance of sun and stars

Of what are shining objects of the sky composed? When man wishes to determine the composition of an ore he gets a sample; then in the chemical laboratory he analyzes it to determine its nature and value. Wishing to learn about the composition of sun and stars, he can take from them only the light that comes to earth and analyze it.

However, this method is now just as accurate as if he could a handful of the star's or sun's substance and subjects it to his analysis. He analyzes the light that comes from these bodies and by careful observation and study learns the story that is has to tell. The first problem is to get enough light to analyze, particularly in the case of less bright stars. The human eye is so small that it can observe only a very narrow beam of light. And optical aid is necessary in order to collect more light and to magnify the far off stars or the sun. This is achieved by the telescope. The essential part of this instrument is a lens or a mirror, which is use to focus the rays on the eye or any scientific instruments.

Some types of telescopes are now in use. The more common type is the one that employs a lens for focusing the light rays. After the telescope has collected the light, it must be analyzed and studied. Here the spectroscope has given most information. The spectroscope is an instrument that separates into its various colors or waves lengths the light passing through it, a process achieved mostly by means of a transparent prism. Most people have observed the rainbow of colors produced when sunlight shines through a prism.

Sunlight or any white light is made up of a large numbers of waves, each of different wavelengths in passing through a prism, the waves are separated, and these separated waves being what will produce the different colors. A significant fact of nature is that each of the chemical elements - gold, sodium, copper, oxygen, hydrogen, and so on - when brought to luminescence, will always give off a characteristic color or a definite wavelength of light. Sodium, for example, will always give off a yellow light which, when passed through the spectroscope, will be separated into it various wavelengths. These wave lengths appear as bright lines in the spectrum, and no other light except that from sodium will show these particular lines.

Any light source may have its chemical composition determined by measuring accurately the lines that appear in its spectrum. Here then is a method of determining the composition of the stars and the sun by analyzing the light that comes from those far-off bodies.

The semiconductor diode

A seven - story high intercontinental missile goes skyward on a column of fire. Within the silvery giant, hundreds of tiny semiconductor diodes control its every movement.

A television camera is focused on ma. Millions of viewers are watching. Between the man and the million of viewers are dozens of semiconductor diodes - without them the television would not function

Older than radio itself, semiconductor diodes today are the workhorses of the electronic industry. They form the heart of nearly all electronic computers - the giant electronic brains that can control a manufacturing plant. They make radar possible. Semiconductor diodes detect radio signals and generate those same signals. Their having so many uses allowed them to find their way into every branch of modern science and industry.

What are these devices? How do they work? What are their characteristics? How are they using?

In essence, the answers are simple. First of all, a semiconductor diode is a one-way street for electric currents. Due to its having this very characteristic, it will allow the current to flow freely in one direction, but will block it almost completely the other. By making use of this characteristic, the semiconductor diode can perform a wide variety of jobs and is one of our most basic electronic servants.

To understand how a semiconductor diode works, let's go back a little and examine electricity itself. An electric current is simply another name for a flow of electrons - the basic electrical charge found in all elements. Electricity flows when electrons move from one atom of a substance to the next.

In some materials like copper, silver, aluminum and many other metals, the electrons can move easily, and it is because of metals conducting electrons so easily that they are cold conductors.

In other materials - glass, porcelain, rubber, and many plastics - the electrons can move only with great difficulty. In fact, only very few electrons can move at all in these substances, even under great electric pressure. So the flow of electric current through them is blocked. These substances are called insulators.

Between conductors and insulators are many materials, which are neither good conductors nor good insulators. The electrons of their atoms are free to move, but are not as free as in conductor; these substances are being known as semiconductor.

Although there are many semiconductors, only a few are used in electronics. Those most widely used are germanium, silicon, selenium and copper oxide. These particular semiconductors have a strange property. Under certain special conditions, electrons can flow out of them easier than in. Under other conditions, the situation is reversed: electrons come in freely, but have difficulty in getting out.

This strange property making itself evident only upon electrons entering or leaving the semiconductor material, it is useful only when the semiconductor is in contact with a conductor. This contact may be made in two ways: by point contact in which the semiconductor and the conductor make contact at only a single pint; and by surface in which they meet over a broad area.

The semiconductor diode has traveled a long way since its original discovery. From the primitive crystal it has developed and become one of the most basic, most valuable of our electronic servants.

COMMENTARY

in one direction – в одному напрямку

Due to – завдяки

the situation is reversed – ситуація змінюється навпаки

most valuable – найбільш цінних

a strange property – цікава властивість

electric current – електричний струм