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with over a thousand volts applied to its plate whereas the maximum allowable voltage for a transistor is
limited to about 200 volts (usually 50 volts or less). A tube can also handle thousands of watts of power.
The maximum power output for transistor generally ranges from 30 milliwatts to slightly over 100 watts.
When it comes to ruggedness and life expectancy, the tube is still in competition. Design and
functional requirements usually dictate the choice of device. However, semiconductor devices are rugged
and long-lived. They can be constructed to withstand extreme vibration and mechanical shock. They have
been known to withstand impacts that would completely shatter an ordinary electron tube. Although some
specially designed tubes render extensive service, the life expectancy of transistors is better than three to
four times that of ordinary electronic tubes. There is no known failure mechanism (such as an open
filament in a tube) to limit the semiconductor’s life. However, semiconductor devices do have some
limitations. They are usually affected more by temperature, humidity, and radiation than tubes are.
Q3. Name three of the largest users of semiconductor devices.
Q4. State one requirement of an electron tube, which does not exist for semiconductors, that makes the
tube less efficient than the semiconductor.
SEMICONDUCTOR THEORY
To understand why solid-state devices function as they do, we will have to examine closely the
composition and nature of semiconductors. This entails theory that is fundamental to the study of solid-
state devices.
Rather than beginning with theory, let’s first become reacquainted with some of the basic
information you studied earlier concerning matter and energy (NEETS, Module 1).
ATOMIC STRUCTURE
The universe, as we know it today, is divided into two parts: matter and energy. Matter, which is our
main concern at this time, is anything that occupies space and has weight. Rocks, water, air, automobiles,
clothing, and even our own bodies are good examples of matter. From this, we can conclude that matter
may be found in any one of three states: SOLIDS, LIQUIDS, and GASES. All matter is composed of
either an element or combination of elements. As you know, an element is a substance that cannot be
reduced to a simpler form by chemical means. Examples of elements with which you are in contact
everyday are iron, gold, silver, copper, and oxygen. At present, there are over 100 known elements of
which all matter is composed.
As we work our way down the size scale, we come to the atom, the smallest particle into which an
element can be broken down and still retain all its original properties. The atoms of one element,
however, differ from the atoms of all other elements. Since there are over 100 known elements, there
must be over 100 different atoms, or a different atom for each element.
Now let us consider more than one element at a time. This brings us to the term "compound." A
compound is a chemical combination of two or more elements. Water, table salt, ethyl alcohol, and
ammonia are all examples of compounds. The smallest part of a compound, which has all the
characteristics of the compound, is the molecule. Each molecule contains some of the atoms of each of
the elements forming the compound.
Consider sugar, for example. Sugar in general terms is matter, since it occupies space and has
weight. It is also a compound because it consists of two or more elements. Take a lump of sugar and crush
