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Electromagnetic Energy Principles

Energy takes various forms - kinetic, chemical, electrical, sound. One range of related forms is radiant or electromagnetic radiation. Electromagnetic radiation is comprised of electric and magnetic fields that move at right angles to the direction of travel and to each other. It travels at the speed of light. It moves through a vacume, air and various materials depending on the frequency. For example:
  • Low frequency (long wavelength) waves are used to communicate with submarines because they will travel for longer distances through water.
  • Microwaves are used for satellite communications because they are not reflected by the Ionosphere (a layer of the Earth's atmosphere with a high concentration of charged particles, which reflects radio waves).
  • High frequency infrared (IR) energy can penetrate the atmosphere, but lower frequency IR (emitted by objects on earth) is reflected back. (The greenhouse effect)
  • High frequency untraviolet is absorbed by the ozone layer.
  • X-rays and gamma rays will pass through metal, but light and radio waves will not.
  • X-rays are used for medical diagnosis because they penetrate human tissue and expose film and for radiation therapy. However X-rays will not penetrate the atmosphere, so X-ray astronomy must be done from satellites.
  • Infrared radiation results from changes in the energy states of the outer electrons of atoms and molecules, except at absolute zero. Hot objects emit more radiation at a higher frequency than cold objects. Infraed frequenies around 100 THz are asorbed by objects because that is the natural frequency at which most atoms vibrate.

Wave length is inversely proportional to frequency.
lambda (λ)= c/f where lambda is wavelength in meters, c = 2.998 x 108 m/sec. (speed of light in a vacume) and f is the frequency in cycles/sec.
The speed of electricity in copper wire is a more complicated matter. It turns out the electrons actually move very slowly (in DC current), but the electrical charge is passed by electrons "nudging" their neighbours and moves very fast. Alternating current is used to generate electromagnetic energy. In this case the electrons don't move but just vibrate and speed is dependent on things like resistance, inductance,and capacitance (See Electronics 101 ).

Length of a quarter wave line (matching transformer-no end effect)
L = 246 * vf / f
Where 246 = 983.6 (speed of light in million ft./sec.) / 4
Vf = Velocity Factor
Air insulated parallel line 0.975
Air insulated coaxial cable 0.85
Polyethylene parallel line (twin lead) 0.82
Polyethylene coaxial cable 0.66

Band λ f E
AM Radio 500 m 600 KHz 10-9eV
FM, TV 3 m 100 MHz 10-7eV
Radar 30 cm 1 GHz 10-6eV
Microwaves 1 cm 30 GHz 10-5eV
Infrared 10-5 m 1013 Hz 10-2eV
Visible 10-7 m 1015 Hz 1 eV
UV 10-8 m 1016 Hz 10 eV
X rays 10-10 m 1018 Hz 1 KeV
Gamma Rays 10-13 m 1021 Hz 1 MeV
Planck's relation E = hν, where E is the energy of the photon, h = 6.626 ~ 10-34 J•s (Joule Seconds) is Planck's constant, and ν is the frequency of the wave.

Propigation Mobile Phone
The lower band (Cellular/850 MHz) also pepentrates thicker obstructives better than the higher frequency (PCS/1900 MHz).
PCS/1900 MHz travels further.

See Also:
Electromagnetic Spectrum
Electronics 101 at

last updated 17 Mar 2001