Electromagnetic Energy

EME comes in a variety of forms which are used to stimulate a desired effect using the effects of electromagnetic energy. 

Electromagnetc waves are produced whenever an electric charge undergoes an acceleration.  Waves radiate out from the point of acceleration and have both electrical as well as magnetic components.

Wave Motion is an important method of transferring energy without matter being transferred.  Some desriptive terms are listed below:

  • Cycle - One complete Wave
  • Wavelength - Horizontal distance from one point on a wave to the same point on the next wave.
  • Amplitude - Maximum depth or height of a wave.
  • Frequency - Number of cycles per unit of time (usually in cycles per second or Hertz [Hz]).

Below is an illustration of Wave Motion:

Below are a couple of illustrations of the Electromagnetic Spectrum:

Therapists in the physical therapy field use a variety of forms of EME to treat their patients, listed are the types of EME used in physical therapy:

  • Ultraviolet
  • Infrared
  • Shortwave Diathermy
  • Microwave Diathermy
  • Electrical Stimulation

And just to finish up we'll include a few items that may be useful.

Grotthus' Law

  1. Rays must be absorbed to produce their effect.
  2. The effect is produced at the point where the rays are absorbed.

Inverse Square Law

  1. The intensity change of radiation varies inversly with the square of the distance from the source.
  2. Formula - Intensity = 1/Distance2

Cosine Law

  1. Maximum radiation is received if the source is at right angles to the irradiated surface.


  1. Change in direction of waves away from an object.  Dependent on characteristics of surface.


  1. Change in direction of waves passing through an object.