Physical Agents in Rehab- Electromagnetic spectrum and Laws.pptx

Physical Agents in Rehabilitation EM Spectrum and Laws Governing Radiation Electromagnetic spectrum Learning outcomes The student should be able to: 1. Describe the electromagnetic spectrum 2. Outline the sources and uses of waves in the spectrum 3. Explain the characteristics of the...

Physical Agents in Rehabilitation EM Spectrum and Laws Governing Radiation Electromagnetic spectrum Learning outcomes The student should be able to: 1. Describe the electromagnetic spectrum 2. Outline the sources and uses of waves in the spectrum 3. Explain the characteristics of the waves that are relevant to PT 4. Explain the laws governing radiation and how they affect application of physical agents in PT THE ELECTROMAGNETIC SPECTRUM All substances emit radiant energy Energy is emitted as photons Energy is transmitted in the form of e.m waves Waves have a constant velocity but wavelength and frequency differ V = fλ Velocity = 3x 108 m/sec  EM spectrum = An analysis of electromagnetic waves. Waves are arranged in order of wavelength and/or frequency EM spectrum Wavelength - the horizontal distance from one point to the same point on the next wave (meters or nanometers or Angstrom) Frequency- the number of cycles in unit time. One cycle is the sequence of events taking place between a point and the same point on the next wave. Wave The amount of energy increases as wavelength get smaller and tighter  The shorter the wavelength, the higher the frequency The higher the frequency, the higher the energy content Frequency determines depth of penetration of rays into the tissues EM spectrum EM spectrum Wavelength Frequency Name Use (nm) (Hz) 180-400 1.03 x 1015 Ultraviolet Diagnosis -7.5 x 1014 and therapy __________ ________ _________ ______________ Pain, 632 Cold tissue healing 4.74 x 10 14 Laser _________ __________ ________ 800-15,000 _________ Superficial 2 x 1014 – Infrared heat 2 x 1013 contd Wavelength Frequency Name Use 1.5 x 104 - 3 x 108 Microwave Deep Heat 1 x 109 __________ _________ ________ _________ 3 x 109 - 30 107 Shortwave Deep Heat x 109 Diathermy _______________ ________ _________ 30 x 109 - ______________ Longwave Deep heat 300 x 109 diathermy 106 IR, UV, VISIBLE and WIRELESS WAVES IR, visible and uv are produced by heat Rays do not penetrate deeply when absorbed. IR rays, when absorbed, produce heat (Grotthus’ Law) UV rays when absorbed cause chemical reactions. Eg. Formation of Vit. D from 7 D hydrocholesterol contd Wireless waves are produced by high frequency oscillating currents. When absorbed, they produce heat in the tissues Cold laser is produced by light and does not cause heating when absorbed by tissues Characteristics of Waves Characteristics They undergo: Reflection Refraction Absorption Penetration/ Transmission  Reflection Rays may be turned back from the surface they strike. I=R Dependent on -: Wavelength nature of surface angle at which they strike shape of reflector  Reflection from sphere or parabola This shape used for infra- red lamps to allow for even distribution of rays on body surface Reflectors  Refraction Bending of rays when they encounter new medium  Absorption Rays may be absorbed by surface they strike. Proportion absorbed vary with cosine of incident angle. Cosine Law Laws Governing Radiation Laws Law of Inverse squares The intensity of rays from a source varies inversely with the square of the distance from the source. ΔI=1/(Δd)2 Bunsen Roscoe Law of Reciprocity The intensity and duration of the dose of radiant energy are inversely proportional; E=It ; E/t = I; t=E/I contd Cosine Law- Maximum absorption of energy takes place when the source is at right angles to the absorbing surface. Energy absorbed=energy available x Cos θ Cosine 0=1 Cosine 60=.50 What happens to energy absorbed when incident angle is 60?  Grotthus- Drapers Law- The extent of the effect of rays will depend on the amount of energy that is absorbed