Radiation Physics: Cosine Law and Inverse Square Law

Study Notes

IRR is electromagnetic radiation that lies between visible light and microwave radiation, with a wavelength of 760nm to 1 mm.
IRR is a superficial thermal agent that can be subdivided into three regions or bands (A, B, and C) based on its wavelength and absorption characteristics.

Infrared radiations are produced as a result of molecular motion within heated materials.
An increase in temperature above absolute zero results in the vibration or rotation of molecules, leading to the emission of infrared radiations.

Electromagnetic radiation (EMR) is energy in the form of transverse magnetic and electric waves that oscillate in phase perpendicular to each other and perpendicular to the direction of energy propagation.
EMR is produced by virtually every element in the universe and is characterized by its ability to transport energy through space, requiring no transmission medium, and traveling at a constant rate of 300 million meters per second.
EMR has no mass and is composed of pure energy.

Electromagnetic waves have some magnetic and some electrical properties.
They travel as vibrations in electrical and magnetic fields.
The wavelength of electromagnetic waves varies from long (Radio waves) to short (Gamma Rays).

Electromagnetic waves can be reflected, deflected, and absorbed by the media through which they travel.
The human body cannot detect most electromagnetic waves, but they can cause physiological effects as they travel through the body's tissues.
Skin molecules can detect infrared waves because they resonate at infrared frequencies, resulting in absorption of energy and warming of the skin.

The electromagnetic spectrum includes two zones: nonionizing radiation and ionizing radiation.
Nonionizing radiation, including infrared radiation, visible light, and ultraviolet, cannot break molecular bonds or produce ions, and can be used for therapeutic medical applications.
Ionizing radiation, including X-rays and gamma rays, can break molecular bonds to form ions and is either not used clinically or used in very small doses for imaging or to destroy tissue.

Cosine Law: The intensity of radiation varies with the cosine of the angle of incidence, and effective energy is equal to energy multiplied by the cosine of the angle of incidence.
Inverse Square Law: The intensity of radiation from a source is inversely proportional to the square of the distance from that source.
Arndt-Schultz Principle: No reactions or changes can occur in the body tissues if the amount of energy absorbed is insufficient to stimulate the absorbing tissues.
Law of Grotthus-Draper: There is an inverse relationship between the penetration and absorption of energy.

Increase in metabolism: IRR leads to increased metabolic activities within superficial tissues, resulting in improved cell function and tissue healing.
Increase in tissue extensibility: Heating with IRR leads to increased extensibility of connective tissue, making it useful prior to exercise to increase range of motion.
Pain control: IRR leads to relief of pain by increasing pain threshold, stimulating sensory nerves, decreasing muscle spasm, and removing waste products.