absorption

/ab sawrp"sheuhn, -zawrp"-/, n.

1. the act of absorbing.

2. the state or process of being absorbed.

3. assimilation; incorporation: the absorption of small farms into one big one.

4. uptake of substances by a tissue, as of nutrients through the wall of the intestine.

5. a taking in or reception by molecular or chemical action, as of gases or liquids.

6. Physics. the removal of energy or particles from a beam by the medium through which the beam propagates.

7. complete attention or preoccupation; deep engrossment: absorption in one's work.

[1590-1600; < L absorption- (s. of absorptio), equiv. to absorpt(us), ptp. of absorbere to ABSORB + -ion- -ION]

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Transfer of energy from a wave to the medium through which it passes.

The energy of the wave can be reflected, transmitted, or absorbed. If the medium absorbs only a fraction of the energy, it is said to be transparent to that energy. When all energy is absorbed, the medium is opaque. All substances absorb energy to some extent. For instance, the ocean appears transparent to sunlight near the surface, but becomes opaque with depth. Substances absorb specific types of radiation. Rubber is transparent to infrared radiation and X rays, but opaque to visible light. Green glass is transparent to green light but absorbs red and blue light. Absorption of sound is fundamental to acoustics; a soft material absorbs sound energy as the waves strike it.

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▪ physics

      in wave motion, the transfer of the energy of a wave to matter as the wave passes through it. The energy of an acoustic, electromagnetic (electromagnetic radiation), or other wave is proportional to the square of its amplitude—i.e., the maximum displacement or movement of a point on the wave; and, as the wave passes through a substance, its amplitude steadily decreases. If there is only a small fractional absorption of energy, the medium is said to be transparent to that particular radiation, but, if all the energy is lost, the medium is said to be opaque. All known transparent substances show absorption to some extent. For instance, the ocean appears to be transparent to sunlight near the surface, but it becomes opaque with depth.

      Substances are selectively absorbing—that is, they absorb radiation of specific wavelengths. Green glass is transparent to green light but opaque to blue and red; hard rubber is transparent to infrared and X rays but opaque to visible light. Thus, radiation of an unwanted wavelength may be removed from a mixture of waves by letting them pass through an appropriate medium. Those substances that are designed to absorb a particular wavelength or band of wavelengths are called filters.

 As radiation passes through matter, it is absorbed to an extent depending on the nature of the substance and its thickness. A homogeneous substance of a given thickness may be thought of as consisting of a number of equally thin layers. Each layer will absorb the same fraction of the energy that reaches it. The diagram—> shows a beam of waves passing from right to left through a series of layers (d₁, d₂, d₃) of a medium. If the fractional absorption is taken as 33 percent, or ¹/₃, after the beam passes through the first layer d₁, its initial energy (E₀) will be reduced to E₀/3. One-third the energy E₀/3 will be absorbed passing through layer d₂, and the beam will enter layer d₃ with energy ¹/₃ (E₀/3), or (E₀/9). Similarly, each successive layer absorbs one-third of the energy it receives. Thus for radiation of a given wavelength, an infinitesimally thin layer will reduce the energy of a wave by a fractional amount that is proportional to the thickness of the layer. The change in energy as the wave passes through a layer is a constant of the material for a given wavelength and is called its absorption coefficient.

 

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