cosine law(redirected from Law of cosines)
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a rule that optimal irradiation occurs when the source of radiation is at right angles to the center of the area being irradiated.
1. A physical law that describes the relationship between the sides and angles of any triangle.
2. When applied to physical treatment of the body, it describes the effectiveness of radiant energy and the angle at which it strikes tissue. The maximum amount of energy transfer occurs when the energy strikes tissue at a 90° angle. As the angle changes, the effectiveness of the energy is reduced by the multiple of the cosine of the angle: Effective energy = applied energy × cosine of the angle.
See also: law
1. Scattering of light passing through a heterogeneous medium, or being reflected irregularly by a surface, such as a sandblasted opal glass surface. Diffusion by a perfectly diffusing surface occurs in accordance with Lambert's cosine law. In this case, the luminance will be the same, regardless of the viewing direction. 2. The passive movement of ions or molecules through a medium or across a semi-permeable membrane (e.g. the ciliary epithelium) in response to a concentration gradient until equilibrium is reached. It is one of the three mechanisms that create aqueous humour. See diffuse light; diffuse reflection; ultrafiltration.