The EM spectrum is simply a name that scientists have given to the set of
all types of radiation when discussed as a group. Radiation is energy that
travels in waves and spreads out over distance. The visible light that comes
from a lamp in a house and radio waves that come from a radio station are two
types of electromagnetic waves. Other examples are microwaves, infrared light,
ultraviolet light, X-rays, and gamma rays.
All EM waves travel at the speed of light in a vacuum and have a
characteristic wavelength (λ) and frequency (f), which can be determined by
using the following equation:
c = λ x f, where c = the
speed of light (3 x 108 m/s)
This formula states that the
wavelength of any EM wave traveling in a vacuum, in meters, multiplied by the
frequency of that same EM wave, in Hz, always equals the speed of light or 3 x
108 m/s or 186,000 miles per second.
Use Activity 3.3.1c to practice
finding either the frequency or the wavelength of an EM wave when the other
value is known. When not traveling in a vacuum, the material affects the
velocity of an EM wave. This is illustrated in Activity 3.3.1a.
EM
waves exhibit the following properties:
- reflection or bouncing
- refraction or bending
- diffraction or spreading around obstacles
- scattering or being redirected by particles
This will be discussed in greater detail later in this module. Also,
the frequency and the wavelength of an EM wave are inversely proportionally to
one another, as shown in Figure
.
There are
a number of properties that apply to all EM waves, including direction,
frequency, wavelength, power, polarization, and phase. The properties which
were not previously defined are shown in Figure
.
This course will focus on these properties as they apply to a portion of the
total EM spectrum that includes radio waves and microwaves. These bands are
collectively referred to as the RF Spectrum. EM waves are energy in the form of
alternating transverse electric and magnetic fields. Learn more about EM fields
and polarization in the Interactive Activities below.