What is the Absorption Coefficient?

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  • Written By: Jason C. Chavis
  • Edited By: Bronwyn Harris
  • Last Modified Date: 23 November 2019
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The absorption coefficient is the effect that certain materials have on on some sort of energy beam as it passes through the substance. Essentially, any type of basic particle or pure energy can be affected by different materials, limiting their speed or permeation capability. Most commonly, this phenomena is seen in different forms of electromagnetic radiation, such as radio or television waves. When a wave, such as light, is easily able to penetrate an object, it is said to maintain a level of transparency. Inversely, when the wave has a harder time passing through a substance, it is considered opaque.

When the absorption coefficient deals with light energy, the Beer-Lambert law defines the parameters of the transparency and opacity of an object. Different types of materials maintain different levels of absorption, causing the light to either be blocked or allowed to pass. The measurement of this is specifically defined as the optical absorption coefficient. Optical energy also suffers from the effects of scattering from certain materials. This occurs from the fact that waves and particles can disperse after passing through substances, such as when sunlight impacts rain and the light spectrum scatters to produce a rainbow.


Sound absorption coefficient is the rate at which sound waves are absorbed by certain materials. Like light and other electromagnetic radiation, sound permeates different substances and can either be blocked or easily pass through the material. Sound, like light, often features the scattering effect, spreading out through a substance. However, sound also has an added property of developing resonance from its impact with certain materials. This resonance is essentially the physical vibration of an object due to the wave impact, causing the sound to reverberate through a substance.

Different materials feature different capacities of absorption coefficients. Radio waves, for instance, can easily pass through materials such as cement, wood and glass with limited reflection of the signal. However, metal maintains properties that prevent the radio waves from penetrating, causing a scattering effect. Light is affected by the level of darkness in an object, as in the case of curtains preventing sunlight from entering a house. The atmosphere itself often limits the impact of particles and energy, providing protection from certain celestial radiation phenomena such as gamma rays.


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