Chemistry Reference
In-Depth Information
FIGURE 6
Waves.
All types of waves are characterized by two features: ampli-
tude and wavelength (or frequency). The amplitude, defined as half the linear
distance between a crest and a trough
(a)
, is a measure of the maximum dis-
placement of a wave. The wavelength is the distance on a straight line along a
wave, from one crest (or trough) to the next
(a)
. The frequency is the number of
times that a repeated event occurs per unit time; the shorter the wavelength of
a wave, the higher is its frequency
(b)
.
Electromagnetic Waves
Electromagnetic waves
are created by moving
electric charges. When an electric charge moves, it creates a
magnetic field
.
If an electric charge
oscillates
(moves back and forth or up and down), its
electric and magnetic fields change together, creating an electromagnetic
wave. Different forms of electromagnetic radiation can be differentiated
by their wavelengths, as listed in Table 6 and illustrated in Figure 7 (Bekefi
and Barrett 1987). After inception, electromagnetic waves propagate
through empty space (vacuum) or through matter, without displacing mass
but displacing energy.
In a
vacuum
(empty space), all forms of electromagnetic radiation
propagate at a velocity of 300,000 km per second, when propagating
through air, water, or any kind of matter, they interact with the matter
and their velocity is reduced. Differences in the manner of interaction
between different forms of radiation and different types of matter
generally reveal information on the nature and the constituents of
matter.
The field of science that studies the interaction of electromagnetic
radiation with matter is known as
spectroscopy
. Spectroscopic studies on
the wavelength, the intensity of the radiation absorbed, emitted, or scat-
tered by a sample, or how the intensity of the radiation changes as a func-
tion of its energy and wavelength, provide accurate tools for studying the
composition and structure of many materials (Davies and Creaser 1991;
Creaser and Davies 1988).
