Page 337 - NS-2 Textbook

Electronics

There are a great many devices used in modern life in wave is produced by a rapidly expanding and collapsing
general and in the Navy that are based on electricity and magnetic field, which is in turn produced by alternately
the electromagnetic wave. Some of these include the energizing and deenergizing an electronic circuit espe-
computer, audio equipment of all kinds, radio l televi- cially designed to generate such ·waves. In elech'onics,
sion, radar, and sonar. Chapter 3 of this unit covered the such a generating circuit is often referred to as an oscilla-
subject of basic electricity. In this chapter we will discuss tor. For many applications an amplifier of some type is
the nature of the electromagnetic wave upon which all of used to boost the power of the oscillator output, and an
the devices mentioned above are based. antenna is used to form the outgoing wave.
In general there are two kinds of waves by type: me- An electromagnetic wave, because of the methods by
chanical and electromagnetic. Mechanical waves require which it is propagated, always resembles a sine wave in
some sort of material in which to travel or propagate appearance. The wave can be described by its wave-
(spread). Many of these can be felt and seen. Examples of length, frequency, and amplitude. In the figure, one com-
this type of wave ,vould be water waves through water, plete electromagnetic wave or cycle is shown, and the
sound waves through aiI~ or vibrations along a taut terms used to describe it are defined as follows:
string. The other type of wave is called electromagnetic, so
• A cycle is one complete sequence of values of the
called because these have both an electrical and a mag-
strength of the wave as it passes through a point in
netic component. This type of wave is non-material and
cannot be directly felt or seen. This type of wave often space.
• The wavelength, abbreviated in electronics by the
h'avels best in a complete vacuum, in which there is no
Greek letter A (lambda), is the length of a cycle ex-
material present. Examples of this kind of wave would
pressed in distance units} usually either meters or
be radio, TV, radar, light, and infrared (heat) waves. The
centimeters.
material or space through which waves h'avel is called
• The amplitude is the wave strength at particular
the 1IIediu1ll.
points along the wave. It is a measure of the en-
Regardless of the type of wave, all need some sort of
ergy contained in the wave. Large amplitude
energy source to originate. Waves can be thought of as
waves convey more energy than do those having
nature's means of dissipating energy from this source.
small amplitude.
They will continue to propagate until the energy level in
the surrounding medium is the same as the energy at the
source location. There are also tvvo kinds of V\Taves classi-
I+---- Wavelength-----+-/
fied by their form. Longitudinal waves cause the medium I I
I I
through which they travel to be displaced back and forth ~Cycle _I
I I
along the path of the wave, like a spring bOlmcing back I I
I I
and forth. SOlmd is a wave of this kind. Transverse waves
cause the medium to be displaced perpendicular to the
direction of travel of the wave in a pattern often called a
sine wave. An example of this kind of wave is that pro-
duced in a stringed instrument when the string is
plucked.
ELECTROMAGNETIC WAVES ~---------------,~----------------~~
~--------Frequency" 3Hertz---------.;-!
All electronic devices use electronlagnetic waves as the
basis of their operation. Very briefly, an electromagnetic Characteristics of a radio wave with a frequency of 3 hertz.

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