All substances with temperature above absolute zero emits radiant energy. (-273 degree Celsius.
Two theories of Energy transmission
1. Quantum theory – photon is produced by electronic or molecular motion of high velocity or by the kinetic energy released from the collision of molecule
2. Electromagnetic wave theory- energy is transmitted by oscillation in the form of electromagnetic wave
“the shorter the wavelength, the higher the frequency”
“the higher the frequency, the higher the energy content”
*wavelength – is the distance from the peak of one wave to the identical peak of the next wave
*frequency-is the number of oscillations or cycles per second
Electromagnetic Spectrum- representation of various waves energies arranged in order of their wavelength, frequency or both ( 0.0001 nm to .5 x 10 15 nm)
Radiant energy can be affected by the medium:
1. Refection- the angle of incident ray is equal to the angle of reflected ray
2. Refraction- the bending of waves when it enters a medium where it’s speed is different
3. Absorption- electromagnetic energy is transformed to other forms of energy such as heat
4. Penetration- measure how deep an electromagnetic energy can penetrate a tissue
Law of Optics
1. Law of Grotthus Draper: waves of different wavelengths produce different effects, and the extent of the effect will be determined by the amount of energy absorbed by the tissue
2. Law of Inverse Square: intensity of the wave is inversely proportional from the square of the distance from the source
3. Lambert’s Cosine Law- maximum absorption of energy occurs when the source is at the right angle to the absorbing surface
4. Bunsen Roscoe Law of Reciprocity: intensity and duration of the dose of radiant energy is inversely proportional
Eneargy= intensity X time
5. Wien’s Law- wavelength is inversely proportional to the absolute temperature
References: Thermal Agents in Rehabilatation by Hecox
Electrophysical Agents in Physiotherapy by Wadsworth
Thermal Agents in Rehabilitation by Wolf
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